A note about the screenshots and the channels I referenced. The garden room guru, and the channels by Ali Dymock and The DIY guy, in fact, all the channels I noted, are excellent for self builders . That isn’t going to get in the way of my analysis in the video. Construction has to be an iterative process where we can focus on the weak points and find better ways of doing them. TH-cam comments is a great way of understanding this, so to hear both sides, you might want to scroll through the comments.
Informative video. Skip the first six and a half mins. Only mentions EDPM membranes though. A bit of research may reveal whether it can be used with other forms of cold applied roofing.
I’m going to embark on building a garden building possibly next year and have seen a lot of what you showed in your vid, so it was helpful to get a bit more info on it. just fully renovated our home and have had numerous crappy experiences with tradespeople. A good few of them have come across as entitled and have wanted to get in and out with maximum return while providing bad quality work. It’s refreshing when I come across one who actually seems to care. I had a chat with a guy that has a decorating company in Windermere area and he said that most domestic trades don’t seem to realise they’re in a service industry and that how you deal with customers and the quality of your work matters. I couldn’t agree more. That’s why I’ll build my own garden building, then I don’t have to put myself through dealing with them again.
@eddiemcboofin1917 It probably is. I’ve filmed a couple of different ways and need to get some time to make up a vid. Thanks a lot for taking the time to comment.
Well said, we only use the green solvent contact adhesive applied to both sides its just as easy when you know what you are doing, even comes as spray system if you prefer.
Great video - really useful content. Just a suggestion, the constant rotating and zooming of the 3d drawings is quite hard to watch and hard to follow. Still images would be fine. The drawn animations work very well though.
Only watched 5 minutes of this and was just about to post exactly the same comment, as much as I want to learn about this subject the constant zooming in and out ( at speed) is making me nauseous.
Yes, would greatly help to slow the graphic movements. I paused & backed up several times as I watched, in order to study the graphics. This start-pause-start cycle made it tricky to glean all the information.
I am a retired Architect. I completely agree, the OSB below the membrane always seemed a bit dodgy. I always thought it was done to give more support when walking over the roof, but had not considered the cost of the glue. Of course although glue more expensive, so is the extra layer of OSB. Although your method is more foolproof, if the VCL is good enough, and can resist screws penetration, the fact that the rubber is slightly permeable should make the OSB on top ok. One of the calculations that should be done is checking the build up of moisture during winter months doesn’t exceed that that gave evaporate during summer.
As a retired architect, I assume you've seen a few things. Have you come across a rotten top OSB deck due to condensation when there was a VCL? Genuinely interested in gathering some evidence.
@ haha…you got me there. I didn’t come across any, but from my technical training, I woke wary of this top OSB layer. You see this detail from major manufacturers, who should know what they are doing. But I think I recall they used a fully bonded system, so no screw holes to compromise the VCL
Making a build project fool proof is my key... You may get away with one build shortcut, but two or three in the same area leads to a failure. Plus my recommendation for UK home owners is to always have and use quite extractor fans + use a dehumidifier to reduce the amount of moisture testing the effectiveness of the VCB and layers above...?
im from the nordics, Denmark specifically, when in most commercial settings, the roof is actually considered as the vapour barrier, with the inside ceiling being structural perforated steel, with the insulation laying on top and then more often than not, asfalt based roofing systems being burned straight onto the insulation. i have never seen a professional roofing company use any glue or peel and stick roofing product, its all old fashioned 2-3 layer asfalt based roofs. the walls are then mostly precast concrete, which go half to one meter further up than the roof itself, and the asfalt based products are bonded onto this rising bit of the wall, allowing the entire roof surface to act as the gutter and control the water, since water management has become a much bigger issue these years with heavier downpour
Exactly this, me too. Have seen plenty of bad cold roofs, contractor rushing, forgetting to properly ventilate. No evidence of someone pulling up a roof and it's rotted due to evaporation. All due to water ingress from above.
Great video , and also completely correct on the stubborn point of view of many builders. Uk construction industry at the tradesman level has so much ground to make up in comparison to the european counterpart. Not a surprise when you look at the general attitude to new technologies vs "how we've always done it".
We seemed to have perfected most things in Victorian times and mostly have been working backwards since the amount of old buildings I've taken apart where the timbers are in perfect condition speaks for itself heat and ventilation are the key also much healthier for the inhabitants of the buildings
Thank you for the great video and I agree with your explanation. Unfortunately I am very worried as I have done more then 50 flat roofs with 18mm wbp on top of the firrings, vlc “alutrix” on top of the plywood, 150mm ecotherm (very well done, fill and seal all the joints) then 18mm tongue and groove OSB mechanical fixed with the “ plastic washers “ then finished with Flexi tec resin 2020 (very expensive material) and I have provided 10year warranty to my clients. Your explanations make sense, but I don’t know what to do with all the roofs that I have done and also with the others that we already have booked. I find it very difficult to use tissued face insulation (no plywood on top) when you have a lot of parapet detail, box gutter detail, skylight upstand, when the flat roof will be used as a balcony, or air source heat pump will be installed on top, etc…. Any suggestions? All the best
@@AgronIlirBilla why would you trust more the author of this video instead of your experience? Have you seen a top layers of a warm roof with VCL rot? Also, would you reckon it would be easier and cheaper to replace the existing top layer of OSB or the bottom one?
@@OmegaLok Me again. Yes, in answer to your question, I have seen rot in a warm flat roof with a VCL. Indeed, I have worked on a number of schools in which whole buildings have had to be demolished and replaced for that very reason. If I say that the plywood on the outside (not OSB) under the single ply membrane was rotten...........It's incredibly difficult to get ply to rot, but it rotted in this build-up. There was an extant vapour barrier. If you can control the moisture in the building properly, which inevitably means a mechanical ventilation system, then the issue seems likely to go away. I fit them in every building I design. But there are millions of houses around the world with OSB or ply sheathing, and without a MVHR system. They're all in danger.
@@MikeAG333 Sorry I am not convinced about a warm roof simply because you say: "whole buildings have had to be demolished" and "There was an extant vapour barrier." and that indicates to me full timber framing with OSB on the outer shell of the walls + membrane (i.e. you're not talking about a warm roof). I've seen this membrane lapped incorrectly several times on TH-cam (Izzy the Bricky had a video), i.e. top section tucked under the bottom section. I've also seen how my contractor incorrectly lapped the DPC over the DPM, me correct the issue, and building control signing off and then describing in their report that I've correctly put the DPC over the DPM... I just can't logically think that condensation will rot a warm roof outer layer of OSB when I compare the other mistakes where water will literally flow into an envelope and rest there forever.
@@OmegaLok Well, I didn't make myself as clear as I thought I had. Yes, it was a warm roof, and yes, there was a vapour barrier. One can't post drawings on TH-cam or I'd sketch the build-up for clarity. The principle of my point is that OSB is also a vapour barrier, and putting a vapour barrier on the outside of a timber construction, be it wall or roof, is a very poor idea in any place where the building is heated. I'm sure you could probably get away with it in a building that is never heated (and which has decent ventilation), but that's not much of Britain, Europe, or North America. Oh, and I have never claimed that the OSB would rot. It will get mouldy ......sorry......it DOES get mouldy, but it's the framing which is at risk from the interstitial condensation, not the OSB (although, as I said, some of the ply in the schools I talked about had turned to compost).
Excellent video, thank you (...but pls minimise the quick zooming in and out of your CAD objects as it makes me feel queasy!). I'd be interested to hear your thoughts about how all this relates to SIPs...?
If you mean, using SIPs as your roof, you need to consider a ventilated roof, since you cannot really bond directly onto the panel. I’ve made a video about it where I show a detail here Warm Roof Design - Calculate Fall, Firring Pieces or Tapered Insulation? th-cam.com/video/sOr0zx1SIAE/w-d-xo.html
Another superb video. Thank you for being so generous with your advice and providing detailed rationale behind each construction detail. In the process of a timber extension build myself and benefitting a lot from your videos.
THANK YOU ..HONEST TRUTHFULL CORRECT INFORMaTION .IV JUST fOUND YOUR CHANAL....do you have any information on building a full build ,how best to insulate a wooden garden room.?❤
If you haven’t already a take on different flat roofing materials with pros and cons along with correct construction would be great content. I think most people define a single best option not taking into account cost and time both of which I see as normally the reasons end construction choice’s are made contrary to the original plan. Love your fair rational views. Please keep up the great work 🙏
Great video, as always. I have just completed a warm roof myself and used an 18mm OSB "top" deck, however I opted to use Fatra rubber membrane, which uses a solvent based adhesive on both surfaces and in addition I used Alutrix VCL which although expensive was very good on the lower deck. The Fatra was done by an approved installer, however he made me remove the thermally broken screws (mushrooms I called them) as they didn't fit flush and he is a bit of perfectionist and wanted a pan flat roof. I was a bit concerned as I had to replace with countersunk 240mm ones, which I know will affect the roof a bit, thermally. However as I will be looking onto the roof I must admit I do prefer a more flush finish. I'm not a fan of the lumps and bumps. Time will tell whether the upper deck rots!
Thanks a lot for sharing your experience. Yes the Alutrix is good solution although the challenge is getting it sealed into your vertical membrane. The plastic discs don’t bother me and it’s easy to make them regular.
Excellent video....thank you. Question. I want to build a deck over a sun-room. Would the insulated panels be ok to install decking materials and support the weight of people using it for a patio deck?
Well finally someone who talks sense. I thought I was going mad seeing how wrong these roofs are built here in Ireland. If I may ask what is your take on installing the vapour barriers under a tile roof? Do you recommend pulling it taught or leaving some slack so the membrane sags between the rafters? I was taught to allow some slack so any rainwater making it past the tiles can flow down freely instead of stopping at each and every furring strip...
Hi. Yes I would lay it slack like you say. I think you mean breather membrane rather than vapour barrier? The vapour barrier is on the warm side of the insulation. Thanks for your comment.
I am currently working on a building that was constructed 12yrs ago and has damp issues to the upper floor ceilings, upon inspection it is found the grp covered flat roofs which could be described as some where between a cold roof and the hybrid, there is no vapour barrier and no ventilation cosequently the decking boards have completely rotted and also the joists have rotted through, also each flat roof is connected to a pitched roof in which 100mm pir has been installed between the rafters tight up to the underside of the roofing felt, laths and concrete tiles on top, bellow this are the ceiling joists with 100mm glass fibre insulation between them, this is a nursing home and as such it kept warm at all times which is evident when i remove a roof tile and lift out a piece of pir and feel the heat escaping. There is a lot of heat and moisture travelling up through the roof structure and so far i have seen little ventilation, i find it hard to believe building regs let this roof design pass, it was a dissaster waiting to happen, all the flat roofs need completely replacing or in this case as there is a 500mm high parapet wall round at least 3 sides of all the flat roofs so i can construct new roof frames over the old ones and negate the need for invasive repairs or opening up the building to the outside, to top it off all the plumbing, ducting, electrics are hidden above a suspended ceiling wich is hanging off the rotten flat roof joists which are boxed in with fire boards, nightmare really, i will have to suspend the old roof from the new roof and introduce plenty of ventilation to take away the moisture before it reaches the new vapour barrier
Great video and explanation. Instead of OSB on top can we use a cement board or "tile baker board" for smoother finish? I believe this will not rot with moisture
Thanks a lot for the kind words. Any inert material will be better than OSB but I would still be worried about moisture getting trapped beneath or within the board rather than being able to slowly breathe out where no board. I’m not understanding the attraction for the top layer when you can save a load of time and bond direct.
Very informative video thank you, there are currently so many conflicting techniques regarding warm/cold roofs. They all make for interesting viewing though. Unfortunately the link to the restricted height option isn't working for me, I can't seem to find it in your video list either. Thanks again
Thanks, good video. The more people that are aware of the potential problems, the better. I regularly see poorly designed and detailed roofs. Some can cause trouble soon after construction. Sad really, as it often costs much the same to do properly. As houses are better insulated and are less draughty, cold bridging is a growing problem.
Interesting video but the dew point should be calculated so it’s in the center of the PIR and that’s why you can have a OSB top deck without fear of it rotting.
I think you’re talking about about the “calculated” dew point which you can determine by defining a couple of variables. You are correct in that it can be in the centre of the PIR, especially in a warm roof. That’s not what I’m talking about in the arguments I’m making. I just tried to keep it simple to avoid confusing jargon. I may make a follow up video to go into the detail of what you’re saying versus what I think is also the case. Thanks for your comment.
@@build-better-things isn’t that the whole point? You’re saying it will rot with certainty while it’s actually in theory, same as, in theory the moisture will not rot your ply in your construction.
I found this video a couple of years after I did my own flat roof. But it turns out that luckily I had my information from the right sources. A&E construction is one of them and they did a great mini how to do series on building a roof using Resitrix membrane and Alutrix vapour barrier. So the construction is 18mm plywood on the rafters, with proper slope. Then Alutrix fixed with the FG35 contact adhesive. 120mm PIR insulation on top of that, glued with PIR foam adhesive and mechanically fixed with 10 screws per each 1,2x1,2m square. On top of that is the Resitrix membrane which comes on rolls and exists of an EPDM top layer and a bitumen layer underneath. The underside is pre-glued which has a peel of plastic film over it to prevent the roll sticking together. The membrane is glued to the insulation directly after applying the FG35 adhesive on the insulation. The edges of the strips overlap and are sealed with an hot air welder. The big advantages of the system is its durability and that I could install it on my own, no way that you can handle let alone lay down a single piece EPDM membrane on your own. The disadvantage is that having to weld the seams is more work, gives potential failure points and requires some skill. I practised on scrap pieces until I had the right setting of the heat and technique to get a proper bond over the 5cm depth of the seam. Things I could have improved on regarding your video is the PIR I used with Aluminium caching and the use of flat plastic washers for my screws instead of the tubular ones. The screw heads show first when snow on the roof starts melting. The screws are only into the full thickness of the plywood but because I used more than advised and also glued the insulation down wind uplift has not caused any issues, the roof has survived 5 storms now. Also the plywood grips the screws better than OSB and is stronger in itself, though a bit more expensive.
Jerry thanks for yet another great informative video. Just in time as I'm in the planning phase of adding an open plan kitchen dinner leading onto the rear garden. I'm going to pass your video onto the architect so they can spec the construction drawings accordingly. It might not go down well, but I'm the paying customer :)
Thank you too. I’ll be interested if you come back with their comments. Construction industry is a sea of conflicting information sometimes, that’s why I over do it with the analysis.
Thank you for the great video! I have 2 questions if I may. If you glue the epdm directly on top of the insulation, where is the moisture then going? Is it then not equally trapped between those two layers? Only there is no osb there to rot away. My second question is, can you walk on the roof (for maintenance), because then you are walking directly on the insulation?
Hi. If you’re using EPDM, then it has a breathable aspect , so moisture and air will slowly dissipate through the compound over a period of days. In the meantime, there is nothing to rot, so the temporarily trapped condensed moisture can do no damage. With OSB, it gets trapped within the strands of the composite and can never breathe out, so the OSB on its middle to upper part remains permanently damp in the area of condensation, and fails eventually. Yes you can walk on the roof for maintenance, and the insulation I use here is designed for same. You will read some of the negative comments saying otherwise, bizarrely , in support of OSB. I can only point you to my walking about on the roof in the video on boots, and you could also refer to the manufacturer’s recommendations for tissue faced insulation. Now if you wanted deck chairs and a balcony and such, I would recommend something different, but that would hold true for OSB sub strata as well, which wood also be prone to failure. Maintenance is fine for the situation we’re talking about. Great questions and thanks for the comment.
I have a flat roof 24 ' by 20'. I need to tie the EPDM in into a 4/12 pitched shingled roof but don't know best application to do that....excellent job on moisture a hard concept to master
I would use a flashing for that. I guess you could take the membrane up and under shingles and lap the sloping membrane over, but need to go through the detail
Not that it changes the method, but the dew point will be somewhere within the insulation, not on the outside. However, I'm certain your method is superior and will eliminate potential rotting. Great video. Cheers
Hi. Yes, I’m not really talking about the calculated dew point, which is a theoretical placement using some variables, I’m talking about the escaped and residual vapour, along with any changes in the dew point that theory doesn’t account for. Thanks a lot for your comment.
Useful information,especially preventing misery later on,;why i am watching videos like this.BUT what is the solution for my curved roof with strawbale insulation ????
What I know about wonderful straw bale insulation is that it’s breathable, when gathered and laid correctly. I’m assuming you would either have the roof membrane on the underside if it’s on top of the joists, a bit like thatch, and, if it’s between the joists, over the top, with your battens and possibly a breather membrane over that. Perhaps someone with greater knowledge will paste their experience here.
Also on your own video of you installing a roof, it looks like your vapour barrier is just loose laid? We usually prime the deck then install the vapour barrier and seam roller all over laps ?
Hi BBT, I like this roof build but what if you need a firmer surface to the upper finish of your roof for pitching a ladder on etc. Any concentrated load could puncture your roof as the insulation layer will give. Thanks in advance.
Hi. It doesn’t matter what the substrate is, insulation or OSB. This is a common misunderstanding. The EPDM will puncture regardless of the firmness of the substrate. If you were regularly using a ladder you would use a spreader plate , or you would build an inverted roof if there was permanent access. Despite some of the comments here, tissue faced PIR provides a very firm substrate.
Very informative and well described. I have over 20 years of experience with grp from a manufacturer/specifier point of view. EPDM is probably the way to go. Grp is fatally flawed on a flat roof. Although I have never had a failure of a roof I have installed, there are too many parameters for your average roofer to comprehend. I have inspected more poorly installed grp roofs than is acceptable. I also take issue with moisture barriers. The roofs I have seen fail catastrophically are the ones installed with moisture barriers. The roof may have a small leak. The home owner is blissfully unaware as the moisture is held in the roof buildup. It will spread throughout the whole roof and no-one knows until it's too late. A simple repair has turned into a major refurbishment of the roof. I haven't seen a roof without a MB affected by condensation, so I will never be convinced it should be used.
great video👌🏽 I’ll be passing it on to Nottinghamshire’s building association 👍🏾 been a flat roofer for the last 20 years(pvc and felting) the sandwich effect of insulation boards is a waste of time and money. The building industry in the uk is so far behind European thinking and implementation it’s harnesses and painful to see🤷♂️
Thanks for this. Difficult to get a 100% visual on what you were trying to show as the gold standard. So it's Breathable membrane, osb, insulation and then epdm?
I think it’s osb then vapour control layer on the warm side, then insulation. This keeps the osb in the warm area meaning it does not get cold enough for the vapour in the air to condense on. A breathable membrane lets vapour through so not what you want because that takes the moisture through and as the temperature decreases as you travel through the insulation eventually you get to the dew point and moisture will condense out. Breathe membranes are for where you want vapour to escape but at the same time be waterproof. I.e. above a 50mm air gap in a cold roof below tiles.
No breathable membrane. OSB then vapour barrier, then insulation, then EPDM. Sorry if I wasn’t clear. You only use breather membrane where you have a ventilated cavity on the cold side of the membrane.
Hi Jerry Many thanks first-of-all for your interesting videos. Looking at the video, what came to my mind is: How does the roof construction apply to warmer regions like mid/south Italy or Spain where summers are very hot (winters mild) . Would YOU build the roof the same as you demo in your video? Same insulation materials? Thx
These are the climates where thermal bridging makes the biggest impact. Especially in New construction where through ventilation isn’t done anymore and housing is closer to airtight , even in southern Europe. People associate thermal bridging with heat loss, but it has a bigger impact on keeping interiors cool and comfortable in hot sunny climates, especially in the evenings. You need warm roof and warm wall construction, with the actual structure inside the insulation. I’ve made videos about it elsewhere on the channel. Thanks for your comment.
@@build-better-thingsthank you for your reply, I will search for that video for warmer climates on your channel. I am planning to build a high insulated timber/prefab house probably in mid Italy. I might need your help later on.
The principles apply to peaked and pitched roofs as well, but I didn’t know that until I started paying attention. After the spray foamers came and insulated my attic roof. I haven’t a clue if there was any sealant or member sprayed to the underside of the roof decking before applying the foam. 😅
Don't they have ZIP System or something similar in the UK? Your vapor and water barrier are part of the roof sheathing. Insulation goes on top. Then furring strips to support your roof panels (or another layer of ZIP if you're laying shingles).
Great video, thanks. If I put an Earth roof on top of the EPDM could it be done without any adhesive at all? The weight of The soil could hold down the EPDM. Assume of a roof pitch of 12: 1.
Thank you too. If you’re thinking about earth, you might want to consider an inverted, or upside down roof. I’m not sure that EPDM would do it long term in that situation.
Atlast some clarification, excellent work! Could you advise on how to build a flat roof on top of a single story extension that combats the noise transfer from rain? Thankyou
Hi. Although PIR is not particularly acoustically sound, if you’re building to current regulations, you’ll have 150mm of depth. Couple that with the deck and I don’t think you’ll find the rain noise that invasive. Eliminating sound completely would take some more work, but you’d have to consider then the whole space, including the walls and how the junctions work with the roof.
Damp can only come through condensing vapour as I’m describing, above the vapour retarder, or through moisture coming via a hole or rip in your roof membrane
Yes okay. So you're saying the vapour retarder/membrane which is blow the insulation will stop that? Aside from holes and other sources of moisture....
Hi. Great question. I deliberately avoided talking about the “calculated” dew point because I don’t think it’s relevant to what I’m talking about and it’s not something many might understand. It’s just very hard with the choices of information to focus on in the time you have in ten minutes of video. I’d make a specific video on it but I’ve tried similar before and the interest isn’t there.
Fair point, good to keep the info concise. I agree it's good to keep the details robust and allow an easy way out for moisture. You can never guarantee a perfect installation of a VCL so a theoretical dew point can become slightly irrelevant anyway. I always try to specify details that still work even if they are installed on a Friday afternoon. Cheers.
I prefer a cold deck.. but i put 50mm pir underside of joist and tape the joints then i put a 2x1.5 battons for slab ... the pir taped is my air thightness.. i put it on in full sheets with other cut in between joists
Hi, great video - thanks. Is it possible to apply final layers to say rockwool flexi or such. I'm ocd about fire proofing and toxic fumes with kingspan and it's ilk. Is some form of more non-rottable layer or support system be available to walk on after installation? Cheers
Hi. Which way are you worried about fire proofing. Starting inside and spreading out presumably? Surface spread of flame is one of the main issue with flat roofs. I’m just not 100pc clear on your question. Can you word in a different way? S Thanks.
I mean that if I only wanted to insulate with rockwool and not pir, then it seems a cold roof is my only option as the load bearing capacity on a warm roof is not sufficient for walking on and such in comparison to pir?
Yes that is correct. You need to ventilate between the insulation and the timber deck. But you also must remember, mineral wool is less than half as efficient as PIR, so you’re not going to be even close to the efficiency of rigid.
I'm a little confused: In the case of a warm deck, the vapour barrier prevents moisture in the warm air in the living space from getting to the insulation and beyond, so where does the moisture that's going to rot the underside of the top layer of OSB come from?
Hi. It comes from residual vapour, leaked vapour, the fact that there’s gaps and joints and penetrations which means more vapour still, the fact that there’s not a vacuum on the roof side of the vapour barrier (vapour retarder is a better description ) and, in the case of those using foils in their insulation in a warm roof, from thermally contrasting elements such as metals v inert materials. Put all of that together over a period of years and you have the compounding effect of rot on the top layer of OSB which in turn affects your adhesion . If I was putting the question back to you, it would be, why do you want a top layer of OSB when you can do it more economically without, even if you don’t accept my analysis of rot?
wow the value of this information is just insane.. I'm going to scour your channel for insulation and moisture solutions for the basement. I tried to find what software you use in the comments but to no avail..
9:12 could you please link to your other video? I can't fight the video you are referring to. Thanks for this video, I live in Belgium and unfortunately, we have the same "I have been doing this for 20 years and never had any issue" builders. The problem with these kind of builders is that they got in the craft by "doing" not "understanding".
Please excuse me if this is a daft question. I was totally onboard following your explanation and it made perfect sense, until you mentioned that air pockets between the rubber and the insulation are not a problem as the rubber is slightly permeable and air bubbles will eventually flatten out. So why would this permeability allow the air out of air pockets but trap moisture from the condensation below? Please be gentle in your response, there is every possibility I've misunderstood something. :)
Hi. This permeability will allow some trapped moisture to slowly breathe through beneath the membrane, but it won’t if there’s 18mm of OSB sitting on the cold side above the insulation and the localised vapour areas, where the moisture will get trapped within. It’s a good question and my fault for not explaining it well.
Great video, i have an art deco house all flat roofs and parapets and was shocked how little roofers know about this or choose to ignore it, i get stuck as i get quotes and i know more about the theory than all of them after doing extensive research, my issue is my lack of skill to do it myself, id hap pily try a garden room by the house is another beast, the expense of a tin roof alone makes me want it done correct 1st time….Is the height restriction video out yet as i couldnt find ut
@@Jackzuk The University of Greenwich's Chartered Surveying course related on day one "building is an art, not a science". Books will only get you half way.
Brilliant video. Honest question here though. Why do the instructions of the EDPM roofs say to use a water base glue all over apart from 6” around the edge and to use contact adhesive? And on OSB too ? Surely the people who make, supply and instruct how to fit should know this too ?
For a cold roof, this is the correct advice. For a roof with a ventilated battened cavity, this is the correct advice. For firrings over the insulation , this can be the correct advice. But for warm flat roof??? To answer your question…… Ask yourself why these same companies all supply contact adhesives in much larger tins, and tissue faced roof insulation to go with it, for covering large areas such as the entire roof, for bonding directly onto the insulation. Because of course, you bond directly onto the insulation, for your warm roof every time. Why would you ever use a composite timber material such as OSB in that situation on the cold side? Thanks a lot for your comment. I hope I explain it ok.
As an "old boy" builder, I would always choose a cold roof. I've got a warm roof job coming up (as per spec) and I'm already in a panic about materials being damp and not having anyway to breath out!
A cold roof is a solution for OSB on the cold side, but it’s no longer accepted by building regulations in parts of the country. The other issue with a cold roof is dealing with the thermal bridging, which I cover in my other video. Thanks for your comment.
Also without a layer of OSB on top you might get condensation get stuck underneath the EPDM layer, because that is a barrier. But if you use a proper flat roof PIR product, vapour can not pass through.
Thank you for a very useful explanation! I have a question also: is a vapor barrier any use in conjunction with a sealed hard isolation panel of which the seams are taped? Am I wrong in thinking no vapor can get through taped PIR panels anyway?
Taping is not perfect but close enough. I don’t tape the boards because I don’t think foil insulation should be used in a warm roof, but you’ll see in these comments many arguing otherwise. If you have an effective vapour barrier below, that’s really all to focus on. Appreciate it’s tricky with the conflicting info but all I can do is show my analysis and conclusions like in the video. Best of luck with it.
Your general rule that any moisture will condensate on the cold side of the insulation or inside the insulation itself is the simple but effective rule. That is the most important thing to consider when deciding on how to assemble any wall or roof. Thank you
I'm a lowly DIY'er, half way through his first warm roof (a mere 4 square metres). I did consider gluing the rubber directly to the insulation, but in the end I went with a 9mm OSB3 layer beneath the EPDM because that's what the majority of people seem to recommend, and I wanted a roof that I could walk on to get access to the gutters etc. Have I made a horrible mistake ? Time will tell, I suppose. I tried very hard to leave no gaps in the vapour layer (= Alutrix), and I deliberately chose OSB3 because it can apparently tolerate humid conditions. Kingspan claim that their phenolic insulation ("Kooltherm") is also vapour resistant, so perhaps that will help too. I hope it won't end up worse than the cold unventilated felt roof I replaced, which had the consistency of soggy Wheetabix. Fingers crossed.
I wouldn’t call it that. If the roof fails, hopefully you can peel it off, along with the old OSB, it’s not a huge exercise nor cost to adhere new rubberto, using a new 20mm layer of tissue faced over your old insulation to keep the depth almost the same. Humidity is a site specific thing, so you might be OK. Just wait and see.
Great video and just binged a few others (inc french drain which im looking to do with my cellar and a external sump pump). I also one day want to build a garden room with solar, given the weight, how would you construct this kind of roof?
I’ve planning a solar installation at the moment, flat roof using EPDM, fixings for rail system through the membrane and insulation and into the joists. I hope I will post it here at some point but maybe next year.
Interesting video. Lots of conflicting info on flat roofs. I think most are doomed to fail simply because of a lack of pitch and water lying on it. But one simple question. What is the method if your not using rubber? What about fibreglass(not dryseal) and torch on felt?
It’s more just to avoid anything that can rot, such as timber product, on the cold side of the insulation, not part of a ventilated void, and still under the outer membrane. I just happened to be using EPDM because I understand the technology. If your roof membrane requires a timber sub strata, and you’re attempting a warm roof, ie not a cold roof, then I’m saying I think it’s a significant weakness, and I hope I’ve shown why.
Amazing video and very factual (physics) 😂 I will be ensuring my architect producing building reg and construction drawings follows above. Thank you. 👍
I'm shocked. I've been following some of the pro builders you've highlighted in this video and regarded them all as sound sources to watch for good building practices. I built a garden room following a well known channel. I used a liquid adhesive to glue the EPDM down to a wooden roof deck. The saving grace is that I've kept the garden room uninsulated as it is used as a workshop. However, I am now going to rethink/replan the roofing of our single story house extension. In your video the EPDM of your garden room shows all the tube washers. Is this permanent since I don't want upstairs to look down on a spotty roof. I had understood EPDM to be the best modern solution, but if it looks ugly its a no - which probably means fiberglass is the only alternative ?
You could keep exactly what you have done, but do a cold ventilated roof. Which means the top face of the insulation is 50mm below the inside face of the roof deck and it will work well. You do need to ventilated that 50mm void.
@ the extension is in the planing stage. I was just making the point that i had assumed the way other pro builders have shown on TH-cam was correct. Your explanation is excellent and causing me to replan what I eventually end up doing with the extension roof. Warm roof feels like the right way to go but 100% want to get the roof covering and insulation right and lasting a lifetime. My main concern was whether the epdm after correct install shows no signs of fixing points beneath it? It’s this type of aesthetic detail that is just an important where a roof is visible (unlike most garden rooms).
@phil7309 yes you’ll see the washers below like you can in my video, towards the end. However if you took more time laying them out neatly it probably would look ok. Personally it doesn’t bother me the way it is but you might not like it.
Please please please do yourself a massive favour and don't change your plans based on this video, there are massive problems with it. What other channels do you follow that you refer to?
@@onlyidiotsrespond I’m not an expert so I try to learn from those wiser and with real experience to inform my decisions, ideally so I don’t need to rectify a problem caused by an assumed right way to build something. Certain jobs need to be done correctly and a roof is one of those. So after listening to this video I will be researching this more and making sure I am 100% happy with the way I will eventually insulate and build my roof.
A builder put OSB on my pitched roof. Then Rockwool insulation was planed underneath it between the rafters and over the rafters. There gypsum board. The firts winter I noticed not only condensetion but ice forming on the inside of the OSB. I then stopped the guys that where working on the renovation. Since than in didn't find a solution other then doing my roof again removing the OSB...
@build-better-things no! fortunately, I noticed condensation (ice) while they were still installing rockwool and plasterboard (over the weekend when they weren't working), so I stopped the renovation. I have 12cm EPS outside on the facade up to the eaves. Drilling holes there (14 between all rafters, on one side and 14 on the other) installing some kind of insect protection, opening the ridge where the OSB meet is something I can't do myself. I don't even know if it would work. I have ventilation between roof tiles and OSB, not sure what for... it bothers me that the only definitive solution would be to completely remove the OSB, but that is basically a new roof once again.
I am an approved installer for EPDM and I manage several buildings with flat roofs. The older buildings have a more varied makeup but our newer buildings all have the same warm roof makeup. Joists, 18mm T&G OSB3 glued and screwed to joists, FG35 primer & Alutrix 600 (or similar) VCL, timber upstand to the same depth as insulation, 50-150mm PIR, all joins in PIR sealed with aluminium tape, 18mm T&G OSB3 glued together using PU glue and fixed to the subdeck using thermally broken fixings, fixings are then filled with expanding foam to prevent air pockets and then a 1.5mm EPDM bonded to the top deck using water based glue in the centre and 150-200mm perimeter using contact adhesive. Some of these have been in place since ~2010 and they have no issues. When installing we take pictures and send them to the supplier which gives us a 20 year warranty. The only time there was an issue, the membrane had been pierced in a few places by a screw/nail stuck in a boot and the contractor didn't notice. We do 2 inspections a year and noticed some spongy patches in the top deck. We removed and replaced the membrane and top deck. This roof was ~10 years old and the only damaged top deck sections were within ~1m of the penetrations. If someone drops a sharp item, we have patch kits ready to go. I can see where you are coming from re the timber of the cold side of the insulation but, you are fundamentally wrong about the EPDM at 6:10. It is impermeable but breathable. We have tested this ourselves using a pressure chamber. The EPDM was placed between two chambers, the top chamber was filled with water on top of the EPDM, the bottom chamber was pressurised to 1.5 bar. Bubbles of air were able to pass through the EPDM without any moisture coming through to the dry side. When the EPDM gets hot in the sun, the topdeck bakes and dries out.
Hi and thanks for your perspective. Your reference about the breathable nature of EPDM at 6:10. I’m talking about it in the context of interstitial condensation stuck within the solvents and layers in the upper part of the OSB. It won’t breathe out in that situation. Later on, I mention the slightly breathable nature of EPDM, although I’m talking about it in the context of trapped air. Cannot fathom why you would want to be putting foil layers and composite timber anywhere near the cold side of a warm roof when you can eliminate the possibility of rot and trapped condensation altogether, and save money on materials and labour in the process.
@@build-better-things The reason we go with a top deck is to allow access. Even our lighter people leave indents on all the different solid insulation boards we have trialled. We thought about putting boards or planks down when access is required but they would either be forgotten, not used or there would be splinters coming off the wood. If there is a large pocket of trapped air, it has been installed incorrectly, for small bumps, we've put a block on top of them and the air gets forced out after a week or so. If a suitable vapour barrier has been installed correctly, the insulation is well fitting and the EPDM is well fitted, it should essentially be a closed system. The key with that is not using any wet wood or insulation in the construction process. The moisture added with the water based adhesive can evaporate out through the EPDM. Think about timber frame wall construction, especially stuff from the states where it is the dominant form. The layers from internal go Plaster(?), plasterboard, VCL, studs/rockwool, sheet material, breather membrane and then cladding. Some of the treated studs are quite wet from the pressure treatment and yet overtime they dry out. Moisture can't get through the VCL so it has to migrate out through the sheeting and through the breather membrane. I think about the top deck of a warm roof in the same way. Moisture will evaporate from the surface of the OSB and migrate through the EPDM, this creates an area of low water potential so more moisture moves here to achieve equilibrium. And the process repeats until no more moisture can evaporate. As long as more water vapour is getting out of the system than getting in, it will be bone dry. I think top deck vs EDPM bonded to insulation is a horses for courses thing but the top deck is more fool proof. Another point re maintenance is that if the EPDM gets penetrated, the water gets stuck between the EPDM and the OSB. If the EPDM is bonded straight to the insulation, the water will saturate this instead and then you have to replace all the insulation.
I appreciate your comments but you are wrong about access. There’s no difference in the wear between the two solutions. I don’t have the space here to go into the other points, but in summary, I don’t agree at all. OSB on the cold side with foils remains a detail I could never recommend, and I’m amazed that builders continue to do it for their customers in the UK.
There is absolutely a difference in access. I have personally knelt on EPDM over PIR and put a big dent in it. With regular inspections or leaf clearing, it gets battered. I guess our structural engineer consultants must be wrong 🤔 They sign off and guarantee every roof design so they must be in trouble when all of our roofs fail in a few years.
Structural engineers offering guarantees on flat roof makeup? They just do structure! You said you were an approved installer…don’t you offer the guarantee ? If you want to carry on putting OSB on the cold side of your insulation , with foils in your makeup… as an approved installer….good luck.
Im halfway through my own extension and my roof make up is 18mm ply - fg 25 primer alutrix 600 on and up the timber upstands surrounding 150mm pir - joints taped - 18mm t n g osb 3 glued then 1.5mm edpm im assuming they used waterbased adhesive Since i still have no ceilings underneath would another vapour barrier on the underside of joists like a tyvek airguard stop this from happening or is my make up going to be ok
I would omit the vapour barrier under the joists, and figure out a way of how you’re going to get the Alutrix to join into your vertical vapour barrier to maintain your tightness. It sounds like you’re taping foil faced PIR and then placing a secondary OSB deck over. As I say in the video, you should be substituting that for a tissue insulation product, and rather than taping, if you’re that worried about it, use the interlocking batts. Then you just bond your membrane directly onto the tissue face, using the contact adhesive. You’re aiming to eliminate foils and composites above your vapour barrier.
Interesting that you have not suggested a interstitial condensation calculation. If you do that then you can place a deck on the top of the insulation will be functionally 'cold' and unable to suffer from condensation. Also if you look at the instructions for the water based adhesive, you are supposed to wait until it has dried off - if you have been putting the rubber down wet then you have been doing it wrong
A calculated dew point is not reality, escaped and residual vapour is what I’m talking about. You mention water based adhesive. In the video I say you must use solvent based, and I describe how to apply it, including how to adhere.
Actually I’m not sure. I always thought you needed to renew it after quite short periods. I also think you might need to torch onto a timber sub strata so cold ventilated roof might be best. I’m no expert on felt however. Best of luck with it.
@@build-better-things Thanks for coming back so quick. Yes I think it does need renewing from time to time, but should last a good while - perhaps not as long as best case well laid/prep'd GRP/Rubber. This is to do with an 'already built' outbuilding around 3 years ago, did have OSB sheet under and over PIR. I'll inspect at some point as I'm interested in deterioration of the sheet. Thanks!
So do you think SIPs panels are no good? As you know, a SIPs house literally relies on having an OSB board around the perimeter, on the cold side of the insulation? According to what you say in this video, if I've understand correctly, the external OSB board will rot with time? I find that hard to see.
Sips panels for a roof require an additional ventilated battened space and then the actual roof deck. You could argue it’s a cold ventilated roof. You should not be adhering any membranes directly onto the sips panels. Yes, OSB on the cold side without ventilation will run into all the issues I mention in the video. Don’t you agree?
@@build-better-things So if a builder told me he didn't like putting the insulation directly on top of the insulation, are you saying the way to do it would be to introduce a ventilated battened space on top of the insulation. So your warm roof build up would be insulation, OSB, batten to create ventilated horiz. cavity, osb, waterproofing?
If you are using sips, yes. If you’re not using sips, there are many builders still using foil insulation and OSB on the cold side. I’m saying that’s asking for problems and is avoidable. You should be bonding directly into the insulation with your membrane.
Can you help? Is there any way for me to increase the R-Value of the roof from inside, without removing the rubber and working from top down???? Details: I live in a 1000 sq. ft. ranch house built in 1960. The roof has about a 15 degree slope. When I pull down a piece of ceiling drywall in the open living room, I see a 2x8 rafter with 5 ½ inches of faced batt insulation. Then the roof deck, ½ insulation board and then a white rubber covering on top. Looks like it was all quality done at the time. ---- The 2-3 inch gap between the top of the insulation and the bottom of the deck allows it to breath, with vented soffit. Thank you if you have any ideas, as my web research has been unfruitful.
Hi. As long as you have good ventilation within the void above the existing insulation between the rafters, you could consider adding insulated plasterboard, or insulated drywall it’s probably called where you are, and you should aim for at least 72mm thick, which will have 60mm PIR and is enough to make that difference. For existing set ups such as yours where you have that outer layer of bosses, you should try to calculate the dew point. I suspect the half inch insulation board is doing very little but worth checking anyway.
Great video. My only comment is that cold roofs will always create condensation in the cold roof void and its the ventilation that will dry this out. Water vapour doesnt magically waft out the vents and then condense outside. Ps i have 40 years in construction surveying design and inspection. Pps people are still building cold roofs for some mad reason.
An interesting watch, however... 1. If we're talking about doing a quality job, a high end VCL will preventing the vast majority of vapour entering the roof build up to start with. Better still, if you also use foil backed plasterboard (or VCL under joists) then I dare say you'll probably have almost eliminated any vapour entering the insulation!? 2. If there is sufficient insulation, surely any minuscule amount of vapour won't still be warm when it gets to the top layer of OSB, and therefore won't condense at the top OSB as you suggest? Any thoughts @better-build-things
Your point 1, for a warm roof, you should be having your vapour control above the deck, not below it. Foil back plasterboard is not great for a ceiling. Your point 2, I hear this argument a lot and it baffles me. you’re going to have residual air and escaping vapour to create localised dew points. Why you would therefore ever consider putting OSB on the cold side when you could avoid it. The whole point is to design out your problems by not give them the opportunity to occur in the first place
Interesting. I'm always interested in building science. In Canada where I've be practicing for 35 years in the case of a flat roof in an ICI (industrial commercial institutional) application it's a steel deck, vapour retarder, U-0.031 (R-32) and a modified bitumen roof membrane (we also use EPDM or sheet goods) mechanically fastened. I did a pitched roof 30 years ago that employed 4" thickness of polyisocyanurate insulation with plywood both sides to create an insitu composite panel. Deck screwed through with poly vapour retarder on the warm surface, asphalt building felt and asphalt shingles on the exterior. The building appears to be in great condition, albeit the shingles will have been replaced at least once by now. Perhaps it's because I specify plywood and not OSB. It might be that the vapour retarder is just more effective in blocking moisture ingress. Don't know. I do accept that the vented joist space above the rafters/roof joists is preferred for many applications. Not all conditions are the same.
Thank you for providing this detail. Interesting to hear your experience. I like a ventilated roof detail but in the UK now it’s hard to reach the required u values with it
With the target U value being reduced to 0.11 there is currently a problem of how to buy PIR thick enough to be able to construct such a roof with doubling up the insulation. This poses two possible issues 1) A highly theoretical opportunity for condensation between the two sheets of PIR and 2) Screwing down possibly 240mm of insulation. The first I think is probably not a problem but interested in thoughts and both and also availability of insulation material to meet the new target.
Your point 1, if you are using foil backed insulation, which many builders continue to do, you will have trapped condensation where the two foils butt against each other, regardless of your vapour barrier. Your point 2, I would be aiming for 120 between joists, and around 150 over the top, to get around a theoretical 240mm sheet. You raise an excellent point on the new u values, and I suspect manufacturers will find new ways of increasing the lambda effectiveness, such as KingSpan’s newer phenolic batts.
@@build-better-things if you have insulation between the joists, according to your theory, isn't there a risk of condensation at the OSB deck which is directly ontop of the joists?
The OSB deck would be below the insulation and between the joists, 100mm down, there can never be OSB above any insulation unless a cold roof. I didn’t make that clear. I briefly illustrate it when I mention permitted development. Did I explain it ok?
@@build-better-things not clear at all! Why would there be OSB between the joists? What is this 100mm dimension you refer to? Regardless, in the video you said the vapour becomes trapped by the OSB (as it is so full of glues etc), so surely this is also true with a hybrid roof when the vapor meets the first layer of OSB half way through the construction? Moisture trapped at that point surely the water would cause rot too!?
Didn't know about the timber top deck. I love a resin roof bit my eldest says they are poop, his too so many rotten decks and boldness the resin system. He swears by three layers of torch on. Defo gonna send him this vid. And enquire about tissue backed pir. Don't think I've ever seen it in my local builders yards. 👍🏻
What about when sips panels are used? The foam is completely bonded to the osb when the panels are formed in the factory so no moisture can pass through.
I've looked at the same and the SIPs supplier (SIPs industries in Scotland) told me the minimum angle their product can be used at is 11 degrees and installed as a cold roof
Cold roof is correct for SIPs, although it’s not really cold per se . For the reasons I say in my video regarding OSB on the outer side, you need the ventilation over the cold side.
What would be the logic behind insulating between the ceiling joists with 100mm fibre glass and then insulating between the rafters above that ceiling with 100mm pir, breathable membrane on top of that, it very warm in the loft space and it looks like moisture is collecting in the eaves which is rotting the valley boards and flat roof decks attached to the above pitched roofs
There is no logic in insulation between the joists and then again, insulation between the rafters. You either do one or the other. Both options requires ventilation strategy and that is likely why you are attracting moisture.
@@build-better-things Thanks for the reply, the building in question is a residential care home and is only 12 years old, how did this design get passed building regs, the owner now has an enormous task putting this right not to mention the bill
You're absolutely right. But TR27 is useless. We tried a warm roof with no OSB. TR27 ended up with dents in it every time we stepped or kneeled on it. The fibre facing peeled off at the edges. I need a solid roof that I can put ladders on, not one made out of sponge cake. So I ended up solvent gluing 12mm OSB to the TR27 and then solvent gluing the EPDM to that. Really didn't want to, and I know I'm going to have to replace the roof in 10 years because the OSB will rot. Kingspan/other manufs need to come up with a decent product with a hard deck. Until then we will keep installing OSB because it's the only practical option.
I have not had the same problem, although I use the Resista insulation rather than KingSpan and it’s always very firm to walk on, and you can’t peel the face at all. However, for your specific needs, I think you need to be considering an inverted roof, or integrating a raised deck system similar to if you were adding solar , if you’re putting heavy point loads on, or regular foot traffic , regardless of whether I think it will work with Resista. Your use case is not really what the system is designed for, to be fair to the manufacturers .
You'd want to be able to walk on the roof occasionally to clean sky lights or roof lanterns, or if you need to clean, paint, repair gutters. Having a roof that you can't stand on at all is useless
I said above you can walk very comfortably on the roof using tissue insulation and bonding direct. Being unable to walk on it is just a misconception by folks that have not used the correct product, or have never actually installed and experienced it, or are set on using OSB incorrectly on a flat roof.
@@build-better-thingsbut you didn't do it in practice. What's the point in telling everyone how best to do it when you don't do it yourself? Honest question, with all the conflicting information within this video...please be honest...do you know what you're doing/talking about?
I still think a well ventilated cold roof is the best option for long life. My house has a large flat roof - single layer polyester felt on marine ply deck with full cross ventilation. Its 35 years old and still looks fine.
A note about the screenshots and the channels I referenced. The garden room guru, and the channels by Ali Dymock and The DIY guy, in fact, all the channels I noted, are excellent for self builders . That isn’t going to get in the way of my analysis in the video. Construction has to be an iterative process where we can focus on the weak points and find better ways of doing them. TH-cam comments is a great way of understanding this, so to hear both sides, you might want to scroll through the comments.
Informative video. Skip the first six and a half mins. Only mentions EDPM membranes though. A bit of research may reveal whether it can be used with other forms of cold applied roofing.
I’m going to embark on building a garden building possibly next year and have seen a lot of what you showed in your vid, so it was helpful to get a bit more info on it. just fully renovated our home and have had numerous crappy experiences with tradespeople. A good few of them have come across as entitled and have wanted to get in and out with maximum return while providing bad quality work. It’s refreshing when I come across one who actually seems to care. I had a chat with a guy that has a decorating company in Windermere area and he said that most domestic trades don’t seem to realise they’re in a service industry and that how you deal with customers and the quality of your work matters. I couldn’t agree more. That’s why I’ll build my own garden building, then I don’t have to put myself through dealing with them again.
Thank you very much. I really appreciate that comment
@@build-better-thingsmaybe a vid about types of garden room foundations? It's an equally contested area of building lol
@eddiemcboofin1917 It probably is. I’ve filmed a couple of different ways and need to get some time to make up a vid. Thanks a lot for taking the time to comment.
Well said, we only use the green solvent contact adhesive applied to both sides its just as easy when you know what you are doing, even comes as spray system if you prefer.
Appreciate the video but your graphic display jumps around without clearly showing the problem layers, it’s so confusing. Just something simple.
Agreed. Three arrows, and three roating images - can't make out a darned thing.
@dommoore7785 Yes, I’ve mentioned already in other comments many times I’ll try to do it better next time for you.
Yes, I couldn't keep watching it. The graphics waving around so much and three images and I couldn't focus on which was right wrong or why.
Can’t you pause the video? I’m trying to cram a lot in because I an trying to keep the videos shorter
Great video - really useful content. Just a suggestion, the constant rotating and zooming of the 3d drawings is quite hard to watch and hard to follow. Still images would be fine. The drawn animations work very well though.
Only watched 5 minutes of this and was just about to post exactly the same comment, as much as I want to learn about this subject the constant zooming in and out ( at speed) is making me nauseous.
Yes, would greatly help to slow the graphic movements. I paused & backed up several times as I watched, in order to study the graphics. This start-pause-start cycle made it tricky to glean all the information.
The author should respond to your comment, which is very constructiive advice. He responded to many other posts - it's like he doesn't agree with you.
This is the author, Sir. Thanks for the comments. I’ll take that feedback into account for the next one.
@@build-better-things Yes please do, find a view and leave it there if you can. Have a wonderful week and thanks for sharing. Charles
Can you please make a video on detailing the vapor barrier. 🙏 great video as always
Finally someone talking the truth ❤️👍 Good job 👍
I am a retired Architect.
I completely agree, the OSB below the membrane always seemed a bit dodgy.
I always thought it was done to give more support when walking over the roof, but had not considered the cost of the glue.
Of course although glue more expensive, so is the extra layer of OSB.
Although your method is more foolproof, if the VCL is good enough, and can resist screws penetration, the fact that the rubber is slightly permeable should make the OSB on top ok. One of the calculations that should be done is checking the build up of moisture during winter months doesn’t exceed that that gave evaporate during summer.
As a retired architect, I assume you've seen a few things. Have you come across a rotten top OSB deck due to condensation when there was a VCL? Genuinely interested in gathering some evidence.
@ haha…you got me there. I didn’t come across any, but from my technical training, I woke wary of this top OSB layer.
You see this detail from major manufacturers, who should know what they are doing. But I think I recall they used a fully bonded system, so no screw holes to compromise the VCL
Making a build project fool proof is my key... You may get away with one build shortcut, but two or three in the same area leads to a failure. Plus my recommendation for UK home owners is to always have and use quite extractor fans + use a dehumidifier to reduce the amount of moisture testing the effectiveness of the VCB and layers above...?
im on almost 4 years doing commercial roofing and osb below the membrane sounds absolutely bananas
@@markthomasson5077Hello. Genuine question...why does it "seem a bit dodgy" to you when you have evidence to the contrary?
im from the nordics, Denmark specifically, when in most commercial settings, the roof is actually considered as the vapour barrier, with the inside ceiling being structural perforated steel, with the insulation laying on top and then more often than not, asfalt based roofing systems being burned straight onto the insulation. i have never seen a professional roofing company use any glue or peel and stick roofing product, its all old fashioned 2-3 layer asfalt based roofs. the walls are then mostly precast concrete, which go half to one meter further up than the roof itself, and the asfalt based products are bonded onto this rising bit of the wall, allowing the entire roof surface to act as the gutter and control the water, since water management has become a much bigger issue these years with heavier downpour
Absolutely we set our radiant barriers just above the ceilings air space in the details wow i love those plastic fasteners thank you 🙏
Thank you too Mark
Absolutely superb videos. Love your openness and honesty
Good advice!!
I am building a shed/workshop next year and will follow this method!
Can you show me an example of a failed "deck on top of the insulation"? Just intrested to see it with my own eyes.
Exactly this, me too. Have seen plenty of bad cold roofs, contractor rushing, forgetting to properly ventilate. No evidence of someone pulling up a roof and it's rotted due to evaporation. All due to water ingress from above.
Great video , and also completely correct on the stubborn point of view of many builders. Uk construction industry at the tradesman level has so much ground to make up in comparison to the european counterpart. Not a surprise when you look at the general attitude to new technologies vs "how we've always done it".
Thanks a lot. I’m not trying to be critical of others’ efforts . Just want to look at the science and use it to make us all do it better.
Yes, doing it wrong for a long time (Normalized Deviance) does not make something correct.
We seemed to have perfected most things in Victorian times and mostly have been working backwards since the amount of old buildings I've taken apart where the timbers are in perfect condition speaks for itself heat and ventilation are the key also much healthier for the inhabitants of the buildings
This is a great video. Very thorough and well-explained. I will watch this a few times before I add a new addition. Thanks.
Thanks a lot. Really appreciate the comment.
Thank you for the great video and I agree with your explanation.
Unfortunately I am very worried as I have done more then 50 flat roofs with 18mm wbp on top of the firrings, vlc “alutrix” on top of the plywood, 150mm ecotherm (very well done, fill and seal all the joints) then 18mm tongue and groove OSB mechanical fixed with the “ plastic washers “ then finished with Flexi tec resin 2020 (very expensive material) and I have provided 10year warranty to my clients.
Your explanations make sense, but I don’t know what to do with all the roofs that I have done and also with the others that we already have booked.
I find it very difficult to use tissued face insulation (no plywood on top) when you have a lot of parapet detail, box gutter detail, skylight upstand, when the flat roof will be used as a balcony, or air source heat pump will be installed on top, etc….
Any suggestions?
All the best
@@AgronIlirBilla why would you trust more the author of this video instead of your experience?
Have you seen a top layers of a warm roof with VCL rot?
Also, would you reckon it would be easier and cheaper to replace the existing top layer of OSB or the bottom one?
@@OmegaLok Me again. Yes, in answer to your question, I have seen rot in a warm flat roof with a VCL. Indeed, I have worked on a number of schools in which whole buildings have had to be demolished and replaced for that very reason. If I say that the plywood on the outside (not OSB) under the single ply membrane was rotten...........It's incredibly difficult to get ply to rot, but it rotted in this build-up. There was an extant vapour barrier.
If you can control the moisture in the building properly, which inevitably means a mechanical ventilation system, then the issue seems likely to go away. I fit them in every building I design. But there are millions of houses around the world with OSB or ply sheathing, and without a MVHR system. They're all in danger.
@@MikeAG333 Sorry I am not convinced about a warm roof simply because you say:
"whole buildings have had to be demolished"
and
"There was an extant vapour barrier."
and that indicates to me full timber framing with OSB on the outer shell of the walls + membrane (i.e. you're not talking about a warm roof).
I've seen this membrane lapped incorrectly several times on TH-cam (Izzy the Bricky had a video), i.e. top section tucked under the bottom section.
I've also seen how my contractor incorrectly lapped the DPC over the DPM, me correct the issue, and building control signing off and then describing in their report that I've correctly put the DPC over the DPM...
I just can't logically think that condensation will rot a warm roof outer layer of OSB when I compare the other mistakes where water will literally flow into an envelope and rest there forever.
@@OmegaLok Well, I didn't make myself as clear as I thought I had. Yes, it was a warm roof, and yes, there was a vapour barrier. One can't post drawings on TH-cam or I'd sketch the build-up for clarity.
The principle of my point is that OSB is also a vapour barrier, and putting a vapour barrier on the outside of a timber construction, be it wall or roof, is a very poor idea in any place where the building is heated. I'm sure you could probably get away with it in a building that is never heated (and which has decent ventilation), but that's not much of Britain, Europe, or North America.
Oh, and I have never claimed that the OSB would rot. It will get mouldy ......sorry......it DOES get mouldy, but it's the framing which is at risk from the interstitial condensation, not the OSB (although, as I said, some of the ply in the schools I talked about had turned to compost).
This guy has no qualifications no experience
It’s all what he thinks ignore this
Steve roofer is a far better site on TH-cam he will keep you right
Do you have a buildup for Felt and Fibreglass finishes?
Excellent video, thank you (...but pls minimise the quick zooming in and out of your CAD objects as it makes me feel queasy!). I'd be interested to hear your thoughts about how all this relates to SIPs...?
If you mean, using SIPs as your roof, you need to consider a ventilated roof, since you cannot really bond directly onto the panel. I’ve made a video about it where I show a detail here
Warm Roof Design - Calculate Fall, Firring Pieces or Tapered Insulation?
th-cam.com/video/sOr0zx1SIAE/w-d-xo.html
stumbled across your channel today - very glad i did! so much useful information crammed into your vids in a fuss free style.
subscribing! cheers!!
Another superb video. Thank you for being so generous with your advice and providing detailed rationale behind each construction detail. In the process of a timber extension build myself and benefitting a lot from your videos.
Thank you very much!
THANK YOU ..HONEST TRUTHFULL CORRECT INFORMaTION .IV JUST fOUND YOUR CHANAL....do you have any information on building a full build ,how best to insulate a wooden garden room.?❤
Great video. Personally I can't understand why to risk and choose a flat roof in the climates where rain or snow are persistent.
Exactly, should be at least a particular gradient but that equals in loss of internal height (permitted development)
If you haven’t already a take on different flat roofing materials with pros and cons along with correct construction would be great content.
I think most people define a single best option not taking into account cost and time both of which I see as normally the reasons end construction choice’s are made contrary to the original plan.
Love your fair rational views. Please keep up the great work 🙏
Great video, as always. I have just completed a warm roof myself and used an 18mm OSB "top" deck, however I opted to use Fatra rubber membrane, which uses a solvent based adhesive on both surfaces and in addition I used Alutrix VCL which although expensive was very good on the lower deck. The Fatra was done by an approved installer, however he made me remove the thermally broken screws (mushrooms I called them) as they didn't fit flush and he is a bit of perfectionist and wanted a pan flat roof. I was a bit concerned as I had to replace with countersunk 240mm ones, which I know will affect the roof a bit, thermally. However as I will be looking onto the roof I must admit I do prefer a more flush finish. I'm not a fan of the lumps and bumps. Time will tell whether the upper deck rots!
Thanks a lot for sharing your experience. Yes the Alutrix is good solution although the challenge is getting it sealed into your vertical membrane. The plastic discs don’t bother me and it’s easy to make them regular.
Excellent video....thank you. Question. I want to build a deck over a sun-room. Would the insulated panels be ok to install decking materials and support the weight of people using it for a patio deck?
You need to use an inverted roof for that. Whether OSB or insulation substrate, the EPDM won’t take that traffic over time.
Well finally someone who talks sense. I thought I was going mad seeing how wrong these roofs are built here in Ireland. If I may ask what is your take on installing the vapour barriers under a tile roof? Do you recommend pulling it taught or leaving some slack so the membrane sags between the rafters? I was taught to allow some slack so any rainwater making it past the tiles can flow down freely instead of stopping at each and every furring strip...
Hi. Yes I would lay it slack like you say. I think you mean breather membrane rather than vapour barrier? The vapour barrier is on the warm side of the insulation. Thanks for your comment.
Hi, yes @@build-better-things i meant the breather on the cold side. Thanks for confirming.
I am currently working on a building that was constructed 12yrs ago and has damp issues to the upper floor ceilings, upon inspection it is found the grp covered flat roofs which could be described as some where between a cold roof and the hybrid, there is no vapour barrier and no ventilation cosequently the decking boards have completely rotted and also the joists have rotted through, also each flat roof is connected to a pitched roof in which 100mm pir has been installed between the rafters tight up to the underside of the roofing felt, laths and concrete tiles on top, bellow this are the ceiling joists with 100mm glass fibre insulation between them, this is a nursing home and as such it kept warm at all times which is evident when i remove a roof tile and lift out a piece of pir and feel the heat escaping. There is a lot of heat and moisture travelling up through the roof structure and so far i have seen little ventilation, i find it hard to believe building regs let this roof design pass, it was a dissaster waiting to happen, all the flat roofs need completely replacing or in this case as there is a 500mm high parapet wall round at least 3 sides of all the flat roofs so i can construct new roof frames over the old ones and negate the need for invasive repairs or opening up the building to the outside, to top it off all the plumbing, ducting, electrics are hidden above a suspended ceiling wich is hanging off the rotten flat roof joists which are boxed in with fire boards, nightmare really, i will have to suspend the old roof from the new roof and introduce plenty of ventilation to take away the moisture before it reaches the new vapour barrier
Great video and explanation. Instead of OSB on top can we use a cement board or "tile baker board" for smoother finish? I believe this will not rot with moisture
Thanks a lot for the kind words. Any inert material will be better than OSB but I would still be worried about moisture getting trapped beneath or within the board rather than being able to slowly breathe out where no board. I’m not understanding the attraction for the top layer when you can save a load of time and bond direct.
Very informative video thank you, there are currently so many conflicting techniques regarding warm/cold roofs. They all make for interesting viewing though. Unfortunately the link to the restricted height option isn't working for me, I can't seem to find it in your video list either.
Thanks again
Thanks, good video. The more people that are aware of the potential problems, the better. I regularly see poorly designed and detailed roofs. Some can cause trouble soon after construction. Sad really, as it often costs much the same to do properly. As houses are better insulated and are less draughty, cold bridging is a growing problem.
Thank you for your insights Alan.
Interesting video but the dew point should be calculated so it’s in the center of the PIR and that’s why you can have a OSB top deck without fear of it rotting.
I think you’re talking about about the “calculated” dew point which you can determine by defining a couple of variables. You are correct in that it can be in the centre of the PIR, especially in a warm roof. That’s not what I’m talking about in the arguments I’m making. I just tried to keep it simple to avoid confusing jargon. I may make a follow up video to go into the detail of what you’re saying versus what I think is also the case. Thanks for your comment.
@@build-better-things isn’t that the whole point? You’re saying it will rot with certainty while it’s actually in theory, same as, in theory the moisture will not rot your ply in your construction.
I’m saying that I’m mitigating against that possibility. Having a composite on the cold side provides no mitigation.
At last someone that actually knows and understands the warm roof theory, and why it actually works
can you put a green roof on top of this? Any section drawings? How do you stop skylight frame from rotting?
Do an inverted roof for a green roof. Not a warm roof.
@@build-better-things thanks
I found this video a couple of years after I did my own flat roof. But it turns out that luckily I had my information from the right sources. A&E construction is one of them and they did a great mini how to do series on building a roof using Resitrix membrane and Alutrix vapour barrier.
So the construction is 18mm plywood on the rafters, with proper slope. Then Alutrix fixed with the FG35 contact adhesive. 120mm PIR insulation on top of that, glued with PIR foam adhesive and mechanically fixed with 10 screws per each 1,2x1,2m square. On top of that is the Resitrix membrane which comes on rolls and exists of an EPDM top layer and a bitumen layer underneath. The underside is pre-glued which has a peel of plastic film over it to prevent the roll sticking together. The membrane is glued to the insulation directly after applying the FG35 adhesive on the insulation. The edges of the strips overlap and are sealed with an hot air welder.
The big advantages of the system is its durability and that I could install it on my own, no way that you can handle let alone lay down a single piece EPDM membrane on your own.
The disadvantage is that having to weld the seams is more work, gives potential failure points and requires some skill. I practised on scrap pieces until I had the right setting of the heat and technique to get a proper bond over the 5cm depth of the seam.
Things I could have improved on regarding your video is the PIR I used with Aluminium caching and the use of flat plastic washers for my screws instead of the tubular ones. The screw heads show first when snow on the roof starts melting. The screws are only into the full thickness of the plywood but because I used more than advised and also glued the insulation down wind uplift has not caused any issues, the roof has survived 5 storms now. Also the plywood grips the screws better than OSB and is stronger in itself, though a bit more expensive.
Thanks a lot for the information. Great project. What area is the roof ?
Jerry thanks for yet another great informative video. Just in time as I'm in the planning phase of adding an open plan kitchen dinner leading onto the rear garden. I'm going to pass your video onto the architect so they can spec the construction drawings accordingly. It might not go down well, but I'm the paying customer :)
Thank you too. I’ll be interested if you come back with their comments. Construction industry is a sea of conflicting information sometimes, that’s why I over do it with the analysis.
Thank you for the great video!
I have 2 questions if I may. If you glue the epdm directly on top of the insulation, where is the moisture then going? Is it then not equally trapped between those two layers? Only there is no osb there to rot away.
My second question is, can you walk on the roof (for maintenance), because then you are walking directly on the insulation?
Hi. If you’re using EPDM, then it has a breathable aspect , so moisture and air will slowly dissipate through the compound over a period of days. In the meantime, there is nothing to rot, so the temporarily trapped condensed moisture can do no damage. With OSB, it gets trapped within the strands of the composite and can never breathe out, so the OSB on its middle to upper part remains permanently damp in the area of condensation, and fails eventually.
Yes you can walk on the roof for maintenance, and the insulation I use here is designed for same. You will read some of the negative comments saying otherwise, bizarrely , in support of OSB. I can only point you to my walking about on the roof in the video on boots, and you could also refer to the manufacturer’s recommendations for tissue faced insulation.
Now if you wanted deck chairs and a balcony and such, I would recommend something different, but that would hold true for OSB sub strata as well, which wood also be prone to failure. Maintenance is fine for the situation we’re talking about.
Great questions and thanks for the comment.
Thank you for explaining it further! That was very helpful.
I have a flat roof 24 ' by 20'. I need to tie the EPDM in into a 4/12 pitched shingled roof but don't know best application to do that....excellent job on moisture a hard concept to master
I would use a flashing for that. I guess you could take the membrane up and under shingles and lap the sloping membrane over, but need to go through the detail
What’s the best way to replace an old felt flat roof
Not that it changes the method, but the dew point will be somewhere within the insulation, not on the outside. However, I'm certain your method is superior and will eliminate potential rotting.
Great video. Cheers
Hi. Yes, I’m not really talking about the calculated dew point, which is a theoretical placement using some variables, I’m talking about the escaped and residual vapour, along with any changes in the dew point that theory doesn’t account for. Thanks a lot for your comment.
What type of fasteners are used for the roofing and siding to attach it to the insulation? Do those fasteners have to be plastic too?
If you’re piercing the insulation, you should consider using thermal break fasteners. There are a number of different products
Useful information,especially preventing misery later on,;why i am watching videos like this.BUT what is the solution for my curved roof with strawbale insulation ????
What I know about wonderful straw bale insulation is that it’s breathable, when gathered and laid correctly. I’m assuming you would either have the roof membrane on the underside if it’s on top of the joists, a bit like thatch, and, if it’s between the joists, over the top, with your battens and possibly a breather membrane over that. Perhaps someone with greater knowledge will paste their experience here.
Also on your own video of you installing a roof, it looks like your vapour barrier is just loose laid? We usually prime the deck then install the vapour barrier and seam roller all over laps ?
I said in the video, I’ll talk about the vapour barrier another time.
@ the vapour barrier is the most important element?
I said in the video, I’ll talk about it in another video.
Hi BBT, I like this roof build but what if you need a firmer surface to the upper finish of your roof for pitching a ladder on etc. Any concentrated load could puncture your roof as the insulation layer will give. Thanks in advance.
Hi. It doesn’t matter what the substrate is, insulation or OSB. This is a common misunderstanding. The EPDM will puncture regardless of the firmness of the substrate. If you were regularly using a ladder you would use a spreader plate , or you would build an inverted roof if there was permanent access. Despite some of the comments here, tissue faced PIR provides a very firm substrate.
@ 👍ta v much
Very informative and well described. I have over 20 years of experience with grp from a manufacturer/specifier point of view. EPDM is probably the way to go. Grp is fatally flawed on a flat roof. Although I have never had a failure of a roof I have installed, there are too many parameters for your average roofer to comprehend. I have inspected more poorly installed grp roofs than is acceptable. I also take issue with moisture barriers. The roofs I have seen fail catastrophically are the ones installed with moisture barriers. The roof may have a small leak. The home owner is blissfully unaware as the moisture is held in the roof buildup. It will spread throughout the whole roof and no-one knows until it's too late. A simple repair has turned into a major refurbishment of the roof. I haven't seen a roof without a MB affected by condensation, so I will never be convinced it should be used.
Thanks a lot for the comment. Interesting to read your experience. There’s a few commenting here they will never use EPDM.
great video👌🏽 I’ll be passing it on to Nottinghamshire’s building association 👍🏾 been a flat roofer for the last 20 years(pvc and felting) the sandwich effect of insulation boards is a waste of time and money. The building industry in the uk is so far behind European thinking and implementation it’s harnesses and painful to see🤷♂️
@martindabrowa1565 thanks. Appreciate your comment
Absolutely brilliant video! I wish the 3d renders moved a little slower, but this was great. Thank you
I appreciate that! I’ll try and make the speed a bit more comfortable in the future.
I imagine coming back to this . thanks
Thanks for this. Difficult to get a 100% visual on what you were trying to show as the gold standard.
So it's
Breathable membrane, osb, insulation and then epdm?
i was thinking the same. trying to watch the video again to see if i missed the detail.
I think it’s osb then vapour control layer on the warm side, then insulation. This keeps the osb in the warm area meaning it does not get cold enough for the vapour in the air to condense on. A breathable membrane lets vapour through so not what you want because that takes the moisture through and as the temperature decreases as you travel through the insulation eventually you get to the dew point and moisture will condense out.
Breathe membranes are for where you want vapour to escape but at the same time be waterproof. I.e. above a 50mm air gap in a cold roof below tiles.
No breathable membrane. OSB then vapour barrier, then insulation, then EPDM. Sorry if I wasn’t clear. You only use breather membrane where you have a ventilated cavity on the cold side of the membrane.
@davideyres955 that’s right. Thanks for your comment.
Hi Jerry
Many thanks first-of-all for your interesting videos.
Looking at the video, what came to my mind is: How does the roof construction apply to warmer regions like mid/south Italy or Spain where summers are very hot (winters mild) . Would YOU build the roof the same as you demo in your video? Same insulation materials?
Thx
These are the climates where thermal bridging makes the biggest impact. Especially in New construction where through ventilation isn’t done anymore and housing is closer to airtight , even in southern Europe. People associate thermal bridging with heat loss, but it has a bigger impact on keeping interiors cool and comfortable in hot sunny climates, especially in the evenings. You need warm roof and warm wall construction, with the actual structure inside the insulation. I’ve made videos about it elsewhere on the channel. Thanks for your comment.
@@build-better-thingsthank you for your reply, I will search for that video for warmer climates on your channel. I am planning to build a high insulated timber/prefab house probably in mid Italy.
I might need your help later on.
The principles apply to peaked and pitched roofs as well, but I didn’t know that until I started paying attention. After the spray foamers came and insulated my attic roof. I haven’t a clue if there was any sealant or member sprayed to the underside of the roof decking before applying the foam. 😅
Another smashing video on flat roof construction - thanks for sharing
Don't they have ZIP System or something similar in the UK? Your vapor and water barrier are part of the roof sheathing. Insulation goes on top. Then furring strips to support your roof panels (or another layer of ZIP if you're laying shingles).
Hi. The system you’re describing is a ventilated roof, not a warm roof. I’ve made an another video about that if you have a look.
@@build-better-things No, I'm definitely describing a roof with exterior insulation. Steve Baczek, Matt Risinger, etc.
Great video, thanks. If I put an Earth roof on top of the EPDM could it be done without any adhesive at all? The weight of The soil could hold down the EPDM. Assume of a roof pitch of 12: 1.
Thank you too. If you’re thinking about earth, you might want to consider an inverted, or upside down roof. I’m not sure that EPDM would do it long term in that situation.
Atlast some clarification, excellent work! Could you advise on how to build a flat roof on top of a single story extension that combats the noise transfer from rain? Thankyou
Hi. Although PIR is not particularly acoustically sound, if you’re building to current regulations, you’ll have 150mm of depth. Couple that with the deck and I don’t think you’ll find the rain noise that invasive. Eliminating sound completely would take some more work, but you’d have to consider then the whole space, including the walls and how the junctions work with the roof.
could you share informational sheets that you are using to explain builders the technology of installation?
What about damp then getting into the insulation? Or is that mostly caught by a vapour membrane lower in the roof structure?
Damp can only come through condensing vapour as I’m describing, above the vapour retarder, or through moisture coming via a hole or rip in your roof membrane
Yes okay. So you're saying the vapour retarder/membrane which is blow the insulation will stop that? Aside from holes and other sources of moisture....
It will stop most of it for sure. That’s the aim.
I'd be interested to hear your thoughts on calculated dew point.
Hi. Great question. I deliberately avoided talking about the “calculated” dew point because I don’t think it’s relevant to what I’m talking about and it’s not something many might understand. It’s just very hard with the choices of information to focus on in the time you have in ten minutes of video. I’d make a specific video on it but I’ve tried similar before and the interest isn’t there.
Fair point, good to keep the info concise. I agree it's good to keep the details robust and allow an easy way out for moisture. You can never guarantee a perfect installation of a VCL so a theoretical dew point can become slightly irrelevant anyway. I always try to specify details that still work even if they are installed on a Friday afternoon. Cheers.
My god! Common sense at last! Great video!
Instant subscribe❤❤❤❤❤
Excellent content
I prefer a cold deck.. but i put 50mm pir underside of joist and tape the joints then i put a 2x1.5 battons for slab ... the pir taped is my air thightness.. i put it on in full sheets with other cut in between joists
Yes, that can work but need to get the ventilation working between the joists.
Good video thanks for posting . Agree with other commenters have drawings static non rotating
Yes I’ll take the feedback in. Thanks for the comment.
Hi, great video - thanks. Is it possible to apply final layers to say rockwool flexi or such. I'm ocd about fire proofing and toxic fumes with kingspan and it's ilk. Is some form of more non-rottable layer or support system be available to walk on after installation? Cheers
Hi. Which way are you worried about fire proofing. Starting inside and spreading out presumably? Surface spread of flame is one of the main issue with flat roofs. I’m just not 100pc clear on your question. Can you word in a different way? S Thanks.
I mean that if I only wanted to insulate with rockwool and not pir, then it seems a cold roof is my only option as the load bearing capacity on a warm roof is not sufficient for walking on and such in comparison to pir?
Yes that is correct. You need to ventilate between the insulation and the timber deck. But you also must remember, mineral wool is less than half as efficient as PIR, so you’re not going to be even close to the efficiency of rigid.
Can you share your opinion on internal wall insulation systems such as SWIP please?
I'm a little confused: In the case of a warm deck, the vapour barrier prevents moisture in the warm air in the living space from getting to the insulation and beyond, so where does the moisture that's going to rot the underside of the top layer of OSB come from?
Hi. It comes from residual vapour, leaked vapour, the fact that there’s gaps and joints and penetrations which means more vapour still, the fact that there’s not a vacuum on the roof side of the vapour barrier (vapour retarder is a better description ) and, in the case of those using foils in their insulation in a warm roof, from thermally contrasting elements such as metals v inert materials. Put all of that together over a period of years and you have the compounding effect of rot on the top layer of OSB which in turn affects your adhesion . If I was putting the question back to you, it would be, why do you want a top layer of OSB when you can do it more economically without, even if you don’t accept my analysis of rot?
wow the value of this information is just insane.. I'm going to scour your channel for insulation and moisture solutions for the basement. I tried to find what software you use in the comments but to no avail..
Hi. I made a video about the software and my workflow earlier which you can see. Thanks for your comment.
9:12 could you please link to your other video? I can't fight the video you are referring to. Thanks for this video, I live in Belgium and unfortunately, we have the same "I have been doing this for 20 years and never had any issue" builders. The problem with these kind of builders is that they got in the craft by "doing" not "understanding".
I can’t either but would love to watch it
Hybrid Roof - build the Right Way- avoid overheating, avoid timber deck.
th-cam.com/video/5Xiw04-7Jmg/w-d-xo.html
Except video and advice, thanks for sharing 🏴👌
Please excuse me if this is a daft question.
I was totally onboard following your explanation and it made perfect sense, until you mentioned that air pockets between the rubber and the insulation are not a problem as the rubber is slightly permeable and air bubbles will eventually flatten out. So why would this permeability allow the air out of air pockets but trap moisture from the condensation below?
Please be gentle in your response, there is every possibility I've misunderstood something. :)
Hi. This permeability will allow some trapped moisture to slowly breathe through beneath the membrane, but it won’t if there’s 18mm of OSB sitting on the cold side above the insulation and the localised vapour areas, where the moisture will get trapped within. It’s a good question and my fault for not explaining it well.
Great video, i have an art deco house all flat roofs and parapets and was shocked how little roofers know about this or choose to ignore it, i get stuck as i get quotes and i know more about the theory than all of them after doing extensive research, my issue is my lack of skill to do it myself, id hap pily try a garden room by the house is another beast, the expense of a tin roof alone makes me want it done correct 1st time….Is the height restriction video out yet as i couldnt find ut
@@Jackzuk The University of Greenwich's Chartered Surveying course related on day one "building is an art, not a science". Books will only get you half way.
Brilliant video. Honest question here though. Why do the instructions of the EDPM roofs say to use a water base glue all over apart from 6” around the edge and to use contact adhesive? And on OSB too ? Surely the people who make, supply and instruct how to fit should know this too ?
For a cold roof, this is the correct advice. For a roof with a ventilated battened cavity, this is the correct advice. For firrings over the insulation , this can be the correct advice. But for warm flat roof??? To answer your question…… Ask yourself why these same companies all supply contact adhesives in much larger tins, and tissue faced roof insulation to go with it, for covering large areas such as the entire roof, for bonding directly onto the insulation. Because of course, you bond directly onto the insulation, for your warm roof every time. Why would you ever use a composite timber material such as OSB in that situation on the cold side? Thanks a lot for your comment. I hope I explain it ok.
As an "old boy" builder, I would always choose a cold roof. I've got a warm roof job coming up (as per spec) and I'm already in a panic about materials being damp and not having anyway to breath out!
A cold roof is a solution for OSB on the cold side, but it’s no longer accepted by building regulations in parts of the country. The other issue with a cold roof is dealing with the thermal bridging, which I cover in my other video. Thanks for your comment.
Hi can you link to your 2.5m height restriction video?
Likewise haven't been able to find it. This channel is a fantastic resource as an undergraduate architect
Hybrid Roof - build the Right Way- avoid overheating, avoid timber deck.
th-cam.com/video/5Xiw04-7Jmg/w-d-xo.html
Also without a layer of OSB on top you might get condensation get stuck underneath the EPDM layer, because that is a barrier. But if you use a proper flat roof PIR product, vapour can not pass through.
Hi and thanks for your comment. EPDM is somewhat breathable , so trapped moisture can permeate slowly, but not of its within osb.
Thank you for a very useful explanation! I have a question also: is a vapor barrier any use in conjunction with a sealed hard isolation panel of which the seams are taped? Am I wrong in thinking no vapor can get through taped PIR panels anyway?
Taping is not perfect but close enough. I don’t tape the boards because I don’t think foil insulation should be used in a warm roof, but you’ll see in these comments many arguing otherwise. If you have an effective vapour barrier below, that’s really all to focus on. Appreciate it’s tricky with the conflicting info but all I can do is show my analysis and conclusions like in the video. Best of luck with it.
Your general rule that any moisture will condensate on the cold side of the insulation or inside the insulation itself is the simple but effective rule. That is the most important thing to consider when deciding on how to assemble any wall or roof. Thank you
I'm a lowly DIY'er, half way through his first warm roof (a mere 4 square metres). I did consider gluing the rubber directly to the insulation, but in the end I went with a 9mm OSB3 layer beneath the EPDM because that's what the majority of people seem to recommend, and I wanted a roof that I could walk on to get access to the gutters etc. Have I made a horrible mistake ? Time will tell, I suppose. I tried very hard to leave no gaps in the vapour layer (= Alutrix), and I deliberately chose OSB3 because it can apparently tolerate humid conditions. Kingspan claim that their phenolic insulation ("Kooltherm") is also vapour resistant, so perhaps that will help too. I hope it won't end up worse than the cold unventilated felt roof I replaced, which had the consistency of soggy Wheetabix. Fingers crossed.
I wouldn’t call it that. If the roof fails, hopefully you can peel it off, along with the old OSB, it’s not a huge exercise nor cost to adhere new rubberto, using a new 20mm layer of tissue faced over your old insulation to keep the depth almost the same. Humidity is a site specific thing, so you might be OK. Just wait and see.
Plenty award winning excellent builders on TH-cam have done the same don’t worry
@@macsmith6216👍
Thank you so much for sharing such important topic. Please avoid moving the images so much. Give time to the brain to get what is what. Thank you.
Thanks. Guilty of speeding up to fit it in. I’ll slow it down for next one.
Great video and just binged a few others (inc french drain which im looking to do with my cellar and a external sump pump). I also one day want to build a garden room with solar, given the weight, how would you construct this kind of roof?
I’ve planning a solar installation at the moment, flat roof using EPDM, fixings for rail system through the membrane and insulation and into the joists. I hope I will post it here at some point but maybe next year.
@ Excellent 👌 This is good news! Love your detail and the logical explanation behind stuff. Subbed and will continue watching 🙏
Thank you 😊 But I don't understand why the right diagram doesn't match the end video example?
Interesting video. Lots of conflicting info on flat roofs. I think most are doomed to fail simply because of a lack of pitch and water lying on it. But one simple question. What is the method if your not using rubber? What about fibreglass(not dryseal) and torch on felt?
It’s more just to avoid anything that can rot, such as timber product, on the cold side of the insulation, not part of a ventilated void, and still under the outer membrane. I just happened to be using EPDM because I understand the technology. If your roof membrane requires a timber sub strata, and you’re attempting a warm roof, ie not a cold roof, then I’m saying I think it’s a significant weakness, and I hope I’ve shown why.
Amazing video and very factual (physics) 😂
I will be ensuring my architect producing building reg and construction drawings follows above.
Thank you. 👍
I'm shocked. I've been following some of the pro builders you've highlighted in this video and regarded them all as sound sources to watch for good building practices. I built a garden room following a well known channel. I used a liquid adhesive to glue the EPDM down to a wooden roof deck. The saving grace is that I've kept the garden room uninsulated as it is used as a workshop. However, I am now going to rethink/replan the roofing of our single story house extension. In your video the EPDM of your garden room shows all the tube washers. Is this permanent since I don't want upstairs to look down on a spotty roof. I had understood EPDM to be the best modern solution, but if it looks ugly its a no - which probably means fiberglass is the only alternative ?
You could keep exactly what you have done, but do a cold ventilated roof. Which means the top face of the insulation is 50mm below the inside face of the roof deck and it will work well. You do need to ventilated that 50mm void.
@ the extension is in the planing stage. I was just making the point that i had assumed the way other pro builders have shown on TH-cam was correct. Your explanation is excellent and causing me to replan what I eventually end up doing with the extension roof. Warm roof feels like the right way to go but 100% want to get the roof covering and insulation right and lasting a lifetime. My main concern was whether the epdm after correct install shows no signs of fixing points beneath it? It’s this type of aesthetic detail that is just an important where a roof is visible (unlike most garden rooms).
@phil7309 yes you’ll see the washers below like you can in my video, towards the end. However if you took more time laying them out neatly it probably would look ok. Personally it doesn’t bother me the way it is but you might not like it.
Please please please do yourself a massive favour and don't change your plans based on this video, there are massive problems with it. What other channels do you follow that you refer to?
@@onlyidiotsrespond I’m not an expert so I try to learn from those wiser and with real experience to inform my decisions, ideally so I don’t need to rectify a problem caused by an assumed right way to build something. Certain jobs need to be done correctly and a roof is one of those. So after listening to this video I will be researching this more and making sure I am 100% happy with the way I will eventually insulate and build my roof.
This is a proper job👍👍
A builder put OSB on my pitched roof. Then Rockwool insulation was planed underneath it between the rafters and over the rafters. There gypsum board. The firts winter I noticed not only condensetion but ice forming on the inside of the OSB.
I then stopped the guys that where working on the renovation. Since than in didn't find a solution other then doing my roof again removing the OSB...
They didn’t ventilate between the rockwool and the OSB?
@build-better-things no! fortunately, I noticed condensation (ice) while they were still installing rockwool and plasterboard (over the weekend when they weren't working), so I stopped the renovation.
I have 12cm EPS outside on the facade up to the eaves. Drilling holes there (14 between all rafters, on one side and 14 on the other) installing some kind of insect protection, opening the ridge where the OSB meet is something I can't do myself. I don't even know if it would work.
I have ventilation between roof tiles and OSB, not sure what for...
it bothers me that the only definitive solution would be to completely remove the OSB, but that is basically a new roof once again.
I am an approved installer for EPDM and I manage several buildings with flat roofs. The older buildings have a more varied makeup but our newer buildings all have the same warm roof makeup. Joists, 18mm T&G OSB3 glued and screwed to joists, FG35 primer & Alutrix 600 (or similar) VCL, timber upstand to the same depth as insulation, 50-150mm PIR, all joins in PIR sealed with aluminium tape, 18mm T&G OSB3 glued together using PU glue and fixed to the subdeck using thermally broken fixings, fixings are then filled with expanding foam to prevent air pockets and then a 1.5mm EPDM bonded to the top deck using water based glue in the centre and 150-200mm perimeter using contact adhesive. Some of these have been in place since ~2010 and they have no issues. When installing we take pictures and send them to the supplier which gives us a 20 year warranty. The only time there was an issue, the membrane had been pierced in a few places by a screw/nail stuck in a boot and the contractor didn't notice. We do 2 inspections a year and noticed some spongy patches in the top deck. We removed and replaced the membrane and top deck. This roof was ~10 years old and the only damaged top deck sections were within ~1m of the penetrations. If someone drops a sharp item, we have patch kits ready to go.
I can see where you are coming from re the timber of the cold side of the insulation but, you are fundamentally wrong about the EPDM at 6:10. It is impermeable but breathable. We have tested this ourselves using a pressure chamber. The EPDM was placed between two chambers, the top chamber was filled with water on top of the EPDM, the bottom chamber was pressurised to 1.5 bar. Bubbles of air were able to pass through the EPDM without any moisture coming through to the dry side. When the EPDM gets hot in the sun, the topdeck bakes and dries out.
Hi and thanks for your perspective. Your reference about the breathable nature of EPDM at 6:10. I’m talking about it in the context of interstitial condensation stuck within the solvents and layers in the upper part of the OSB. It won’t breathe out in that situation. Later on, I mention the slightly breathable nature of EPDM, although I’m talking about it in the context of trapped air. Cannot fathom why you would want to be putting foil layers and composite timber anywhere near the cold side of a warm roof when you can eliminate the possibility of rot and trapped condensation altogether, and save money on materials and labour in the process.
@@build-better-things The reason we go with a top deck is to allow access. Even our lighter people leave indents on all the different solid insulation boards we have trialled. We thought about putting boards or planks down when access is required but they would either be forgotten, not used or there would be splinters coming off the wood.
If there is a large pocket of trapped air, it has been installed incorrectly, for small bumps, we've put a block on top of them and the air gets forced out after a week or so. If a suitable vapour barrier has been installed correctly, the insulation is well fitting and the EPDM is well fitted, it should essentially be a closed system. The key with that is not using any wet wood or insulation in the construction process. The moisture added with the water based adhesive can evaporate out through the EPDM.
Think about timber frame wall construction, especially stuff from the states where it is the dominant form. The layers from internal go Plaster(?), plasterboard, VCL, studs/rockwool, sheet material, breather membrane and then cladding. Some of the treated studs are quite wet from the pressure treatment and yet overtime they dry out. Moisture can't get through the VCL so it has to migrate out through the sheeting and through the breather membrane. I think about the top deck of a warm roof in the same way. Moisture will evaporate from the surface of the OSB and migrate through the EPDM, this creates an area of low water potential so more moisture moves here to achieve equilibrium. And the process repeats until no more moisture can evaporate. As long as more water vapour is getting out of the system than getting in, it will be bone dry.
I think top deck vs EDPM bonded to insulation is a horses for courses thing but the top deck is more fool proof. Another point re maintenance is that if the EPDM gets penetrated, the water gets stuck between the EPDM and the OSB. If the EPDM is bonded straight to the insulation, the water will saturate this instead and then you have to replace all the insulation.
I appreciate your comments but you are wrong about access. There’s no difference in the wear between the two solutions. I don’t have the space here to go into the other points, but in summary, I don’t agree at all. OSB on the cold side with foils remains a detail I could never recommend, and I’m amazed that builders continue to do it for their customers in the UK.
There is absolutely a difference in access. I have personally knelt on EPDM over PIR and put a big dent in it. With regular inspections or leaf clearing, it gets battered.
I guess our structural engineer consultants must be wrong 🤔 They sign off and guarantee every roof design so they must be in trouble when all of our roofs fail in a few years.
Structural engineers offering guarantees on flat roof makeup? They just do structure! You said you were an approved installer…don’t you offer the guarantee ? If you want to carry on putting OSB on the cold side of your insulation , with foils in your makeup… as an approved installer….good luck.
Im halfway through my own extension and my roof make up is 18mm ply - fg 25 primer alutrix 600 on and up the timber upstands surrounding 150mm pir - joints taped - 18mm t n g osb 3 glued then 1.5mm edpm im assuming they used waterbased adhesive
Since i still have no ceilings underneath would another vapour barrier on the underside of joists like a tyvek airguard stop this from happening or is my make up going to be ok
I would omit the vapour barrier under the joists, and figure out a way of how you’re going to get the Alutrix to join into your vertical vapour barrier to maintain your tightness. It sounds like you’re taping foil faced PIR and then placing a secondary OSB deck over. As I say in the video, you should be substituting that for a tissue insulation product, and rather than taping, if you’re that worried about it, use the interlocking batts. Then you just bond your membrane directly onto the tissue face, using the contact adhesive. You’re aiming to eliminate foils and composites above your vapour barrier.
Interesting that you have not suggested a interstitial condensation calculation. If you do that then you can place a deck on the top of the insulation will be functionally 'cold' and unable to suffer from condensation. Also if you look at the instructions for the water based adhesive, you are supposed to wait until it has dried off - if you have been putting the rubber down wet then you have been doing it wrong
A calculated dew point is not reality, escaped and residual vapour is what I’m talking about. You mention water based adhesive. In the video I say you must use solvent based, and I describe how to apply it, including how to adhere.
Interesting video, thanks. Out of interest, with a warm deck with torch felt over, what's that like for reliability? Asking for a friend 🙂
Actually I’m not sure. I always thought you needed to renew it after quite short periods. I also think you might need to torch onto a timber sub strata so cold ventilated roof might be best. I’m no expert on felt however. Best of luck with it.
@@build-better-things Thanks for coming back so quick. Yes I think it does need renewing from time to time, but should last a good while - perhaps not as long as best case well laid/prep'd GRP/Rubber.
This is to do with an 'already built' outbuilding around 3 years ago, did have OSB sheet under and over PIR. I'll inspect at some point as I'm interested in deterioration of the sheet. Thanks!
Best of luck with it
So do you think SIPs panels are no good? As you know, a SIPs house literally relies on having an OSB board around the perimeter, on the cold side of the insulation? According to what you say in this video, if I've understand correctly, the external OSB board will rot with time? I find that hard to see.
Sips panels for a roof require an additional ventilated battened space and then the actual roof deck. You could argue it’s a cold ventilated roof. You should not be adhering any membranes directly onto the sips panels. Yes, OSB on the cold side without ventilation will run into all the issues I mention in the video. Don’t you agree?
@@build-better-things So if a builder told me he didn't like putting the insulation directly on top of the insulation, are you saying the way to do it would be to introduce a ventilated battened space on top of the insulation. So your warm roof build up would be insulation, OSB, batten to create ventilated horiz. cavity, osb, waterproofing?
If you are using sips, yes. If you’re not using sips, there are many builders still using foil insulation and OSB on the cold side. I’m saying that’s asking for problems and is avoidable. You should be bonding directly into the insulation with your membrane.
Can you help? Is there any way for me to increase the R-Value of the roof from inside, without removing the rubber and working from top down???? Details: I live in a 1000 sq. ft. ranch house built in 1960. The roof has about a 15 degree slope. When I pull down a piece of ceiling drywall in the open living room, I see a 2x8 rafter with 5 ½ inches of faced batt insulation. Then the roof deck, ½ insulation board and then a white rubber covering on top. Looks like it was all quality done at the time. ---- The 2-3 inch gap between the top of the insulation and the bottom of the deck allows it to breath, with vented soffit. Thank you if you have any ideas, as my web research has been unfruitful.
Hi. As long as you have good ventilation within the void above the existing insulation between the rafters, you could consider adding insulated plasterboard, or insulated drywall it’s probably called where you are, and you should aim for at least 72mm thick, which will have 60mm PIR and is enough to make that difference. For existing set ups such as yours where you have that outer layer of bosses, you should try to calculate the dew point. I suspect the half inch insulation board is doing very little but worth checking anyway.
Thank you! Will ck it out!! Appreciate the advice!
Great video. My only comment is that cold roofs will always create condensation in the cold roof void and its the ventilation that will dry this out. Water vapour doesnt magically waft out the vents and then condense outside. Ps i have 40 years in construction surveying design and inspection. Pps people are still building cold roofs for some mad reason.
Thanks. Yes you definitely need ventilation and need to understand how the placement of the vents creates the movement to deal with the moisture.
Because some people are restricted because of height
An interesting watch, however...
1. If we're talking about doing a quality job, a high end VCL will preventing the vast majority of vapour entering the roof build up to start with. Better still, if you also use foil backed plasterboard (or VCL under joists) then I dare say you'll probably have almost eliminated any vapour entering the insulation!?
2. If there is sufficient insulation, surely any minuscule amount of vapour won't still be warm when it gets to the top layer of OSB, and therefore won't condense at the top OSB as you suggest?
Any thoughts @better-build-things
Your point 1, for a warm roof, you should be having your vapour control above the deck, not below it. Foil back plasterboard is not great for a ceiling. Your point 2, I hear this argument a lot and it baffles me. you’re going to have residual air and escaping vapour to create localised dew points. Why you would therefore ever consider putting OSB on the cold side when you could avoid it. The whole point is to design out your problems by not give them the opportunity to occur in the first place
Interesting. I'm always interested in building science. In Canada where I've be practicing for 35 years in the case of a flat roof in an ICI (industrial commercial institutional) application it's a steel deck, vapour retarder, U-0.031 (R-32) and a modified bitumen roof membrane (we also use EPDM or sheet goods) mechanically fastened.
I did a pitched roof 30 years ago that employed 4" thickness of polyisocyanurate insulation with plywood both sides to create an insitu composite panel. Deck screwed through with poly vapour retarder on the warm surface, asphalt building felt and asphalt shingles on the exterior. The building appears to be in great condition, albeit the shingles will have been replaced at least once by now. Perhaps it's because I specify plywood and not OSB. It might be that the vapour retarder is just more effective in blocking moisture ingress. Don't know. I do accept that the vented joist space above the rafters/roof joists is preferred for many applications. Not all conditions are the same.
Thank you for providing this detail. Interesting to hear your experience. I like a ventilated roof detail but in the UK now it’s hard to reach the required u values with it
How do they apply membrane to parapet on Adobe style build? It can't wrap over the top where the stucco is
With the target U value being reduced to 0.11 there is currently a problem of how to buy PIR thick enough to be able to construct such a roof with doubling up the insulation. This poses two possible issues 1) A highly theoretical opportunity for condensation between the two sheets of PIR and 2) Screwing down possibly 240mm of insulation. The first I think is probably not a problem but interested in thoughts and both and also availability of insulation material to meet the new target.
Your point 1, if you are using foil backed insulation, which many builders continue to do, you will have trapped condensation where the two foils butt against each other, regardless of your vapour barrier. Your point 2, I would be aiming for 120 between joists, and around 150 over the top, to get around a theoretical 240mm sheet. You raise an excellent point on the new u values, and I suspect manufacturers will find new ways of increasing the lambda effectiveness, such as KingSpan’s newer phenolic batts.
@@build-better-things if you have insulation between the joists, according to your theory, isn't there a risk of condensation at the OSB deck which is directly ontop of the joists?
The OSB deck would be below the insulation and between the joists, 100mm down, there can never be OSB above any insulation unless a cold roof. I didn’t make that clear. I briefly illustrate it when I mention permitted development. Did I explain it ok?
@@build-better-things not clear at all! Why would there be OSB between the joists? What is this 100mm dimension you refer to?
Regardless, in the video you said the vapour becomes trapped by the OSB (as it is so full of glues etc), so surely this is also true with a hybrid roof when the vapor meets the first layer of OSB half way through the construction? Moisture trapped at that point surely the water would cause rot too!?
@philbooth319 take some time to reread my comment and it should make sense.
Didn't know about the timber top deck. I love a resin roof bit my eldest says they are poop, his too so many rotten decks and boldness the resin system. He swears by three layers of torch on. Defo gonna send him this vid. And enquire about tissue backed pir. Don't think I've ever seen it in my local builders yards. 👍🏻
What about when sips panels are used? The foam is completely bonded to the osb when the panels are formed in the factory so no moisture can pass through.
I've looked at the same and the SIPs supplier (SIPs industries in Scotland) told me the minimum angle their product can be used at is 11 degrees and installed as a cold roof
Cold roof is correct for SIPs, although it’s not really cold per se . For the reasons I say in my video regarding OSB on the outer side, you need the ventilation over the cold side.
What about the new multi foil details im seeing these days
What would be the logic behind insulating between the ceiling joists with 100mm fibre glass and then insulating between the rafters above that ceiling with 100mm pir, breathable membrane on top of that, it very warm in the loft space and it looks like moisture is collecting in the eaves which is rotting the valley boards and flat roof decks attached to the above pitched roofs
There is no logic in insulation between the joists and then again, insulation between the rafters. You either do one or the other. Both options requires ventilation strategy and that is likely why you are attracting moisture.
@@build-better-things Thanks for the reply, the building in question is a residential care home and is only 12 years old, how did this design get passed building regs, the owner now has an enormous task putting this right not to mention the bill
You're absolutely right. But TR27 is useless. We tried a warm roof with no OSB. TR27 ended up with dents in it every time we stepped or kneeled on it. The fibre facing peeled off at the edges. I need a solid roof that I can put ladders on, not one made out of sponge cake. So I ended up solvent gluing 12mm OSB to the TR27 and then solvent gluing the EPDM to that. Really didn't want to, and I know I'm going to have to replace the roof in 10 years because the OSB will rot.
Kingspan/other manufs need to come up with a decent product with a hard deck. Until then we will keep installing OSB because it's the only practical option.
I have not had the same problem, although I use the Resista insulation rather than KingSpan and it’s always very firm to walk on, and you can’t peel the face at all. However, for your specific needs, I think you need to be considering an inverted roof, or integrating a raised deck system similar to if you were adding solar , if you’re putting heavy point loads on, or regular foot traffic , regardless of whether I think it will work with Resista. Your use case is not really what the system is designed for, to be fair to the manufacturers .
You'd want to be able to walk on the roof occasionally to clean sky lights or roof lanterns, or if you need to clean, paint, repair gutters. Having a roof that you can't stand on at all is useless
I said above you can walk very comfortably on the roof using tissue insulation and bonding direct. Being unable to walk on it is just a misconception by folks that have not used the correct product, or have never actually installed and experienced it, or are set on using OSB incorrectly on a flat roof.
what are you doing on the four 150mm cut edges - surely vapour will get in there much more than through epdm or osb ?
I don’t understand what you mean. Can you explain it in a different way so I can respond?
@@build-better-things theres vapour barriers top and bottom but not at the 4 sides of the kingspan, or is there?
I describe how that works in detail in the early part of the video, photos of typical installation along with a diagram.
@@build-better-thingsbut you didn't do it in practice. What's the point in telling everyone how best to do it when you don't do it yourself? Honest question, with all the conflicting information within this video...please be honest...do you know what you're doing/talking about?
@@DICEGEORGEit's not there is it. Hello said one thing, did another and trying to tell you that you don't understand!
I still think a well ventilated cold roof is the best option for long life. My house has a large flat roof - single layer polyester felt on marine ply deck with full cross ventilation. Its 35 years old and still looks fine.
Thanks. Felt has done well. Are you in uk?
@@build-better-things Yes, South of England