As a former Building Control surveyor this was such a common issue, both on new extensions, replacement flat roofs, and even on large new housing developments. On domestic work I would probably say this simple point was missed getting on for 50% of the jobs that I saw at this stage. The issue is that many builders build the walls as they always did with ventilated cold roofs, stopping the walls at plate height. This also applied to the walls parallel to the joists leaving an uninsulated void between the top of the wall, the deck and the joists either side, with only at best a 25mm gap to get the insulation into the void when the issue was pointed out. It really isnt good enough to just fill up the space with quilt as this can create condensation issues, it really needs to be PIR as Steve shows here foamed into place. Another important factor when upgrading a ventilated cold roof to a warm roof is that you need to remove all the old roof insulation from between the existing joists, leaving it in place, particularly if there is a good thickness, means that the vapour barrier under the new insulation will not be at room temperature and can cause condensation problems that the warm roof was designed to overcome.
Yes you are absolutely right 50% though I think is low I'd say 95% of everything I see they haven't done it correctly. Your point about leaving insulation between the joists if you are converting from a cold roof to a warm roof is also totally correct. Personally, I like to go on a rule of thumb 2/3 of the thermal insulation must be above the air vapour control layer to therefore assessment needs to be made about how much insulation is left below if it is old fluffy stuff it's probably not that good so it can stay there if however it's more substantial and well fitted then it may have to be removed.
We bought a house and the previous owner was really proud of the money he'd spent on insulation. We'd have bought the house regardless, but after we bought it I realised he'd wasted his money because the people who had installed it had left big gaps which allowed airflow. We're slowly working on it ourselves now, but this video was great as it showed me I was right about the issues, and my approach has been more or less correct, too. Thank you!
Thank you very much for the comments this is the problem I'm finding so many insulated properties even new builds that haven't been insulated correctly.
@@SteveRoofer There's an awful lot of folks that think they know what they're doing, but lack the critical skills to look at it and see the obvious issues. And of course, they don't bother to check up on the latest info or anything. "This is the way I've been doing it for a decade." And of course the, "That'll do," mentality.
Wish I'd seen your advice years back. Educating people on how to do it right no matter the cost is always worth it. But everyone wants it done cheap and fast.
Don’t believe majority of customers want cheap and fast. Builders however yes despite customers paying for a proper job and when it’s finished don’t know if it’s been done properly.
We had new extension done few years ago using the warm room method and they didn’t fill the gap with insulation between joists, our new extension was absolutely freezing in the winter. I showed the builder your video on thermal bridging and they took the fascia board down and corrected it and now it feels warm and cozy. Thanks for these educational videos
Dear steve et Al. I have just pulled 1500 kg of lead off my annexe which after 20 years was like a burst sofa. It was laid on a warm roof done badly with no vapour barrier. I have stripped it and used Allutrix then put Res Tech flexible fibreglass over the new deck. Vapour barrier and thermal bridging control is critical when working on modern roof systems. Thanks for a very good video.
If you completely seal up roofs like that the timber will rot out double quick . Sealing everything up causes all sorts of problems and we leave air gaps on purpose you will cause mould, condensation and damp .
Interesting point, I to have been wracking my brains about how to insulate effectively without trapping moisture, I have tried to strike a balance but its difficult to avoid condensation finding cold unventilated areas. Problem seems to be that we won't find out for 10 years if it's going rotten!
@@jonwilmot5331 we know that not using Vapor barriers and ventilation timbers go rotten that’s why we ventilate loft spaces , bathrooms, flat roofs and put vents on double glazed windows.
When we built our lofty on a 3 bed semi we spent ages and a lot of money insulating the roof and walls and getting obsesive about draught proofing. In the last three years since we have never turned on the reads up here, the loft stays very cosy all winter with just the heat leaking up from downstairs. To be fair though you do need a forward looking customer to agree the extra costs involved in getting it right, done well though a few years of reduced heating bills and you have paid for it. Good video, thank you.
Did I read somewhere that you been a flow of air in the foot area to prevent moisture build up and mold - which is why soffit boards have holes in them to allow for breathing?
Soffit boards have holes if you need the ventilation between where you’ve insulated and the outside world. Typically a cold roof. What Steve is demonstrating here is warm roof design where you are creating the thermal envelope around the end of the soffit. Moisture in buildings is typically caused by warmer moist aire hitting something that is colder and the coldness is below the dew point for the warm humid air causing the water vapour to condense and turn in to water on the colder surface. If this is wood then you have the ideal environment for mould and rot. Because it’s hidden behind plasterboard or something else you don’t realise until it’s starting to show up which is too late and big bills are due.
Thanks Steve, great vid as always. I think what you have to remember is warm air is attracted to cold air, so if you have these tight gaps the air fairly whistles out. It would be interesting to compare say 18mm ply totally sealed at the edges with insulation with gaps in that area.
Years ago we had a kitchen done with a warm roof, the builders did a horrendous job, large gaps, they blocked roof vents because they couldn't be bothered to trim them down, it was so bad I took it down and redid it. Reading a few comments here, it seems that most of the mistakes are down to builders, the so called professionals! Hence why I do most things myself, if you want something doing correctly do it yourself.
Thanks for the info. Had a flat roof extension done last year and it saddens me that i know for a fact this tucking in was NOT done. So this summer it’s fascia’s off and do it properly … Myself 😢
I thought that you had to leave a space where the ceiling insulation meets the soffit for ventilation of air to be able to get in and stop roof condensation?
The moisture in air condenses where warm moist air contacts a cold surface. Hence if the roof structure is fully insulated without cold air ingress or cold bridging, the moisture won't condense as the insulation internal face is at or close to the ambient air temp.
Very good video Steve. Thanks for the info. I always thought (or think I was told when I did my Carpentry & Joinery course between '94-'97) that you had to leave a gap between floorboards for air to circulate. I guess this has now been superseded in today's world? Thanks once again and ATB
Hi. Interesting video. But perhaps you could do another to clear up some confusion. Especially for owner of older houses that require ventilation in their rooves to stop condensation. I have tried this method with my new roof and quickly discovered that the roof needed air movement yet I still would like to be able to some how seal out the cold air from out side getting into the inner space on the other side of the insulation. How do we do that?
If it requires ventilation, and is an older property, I'm assuming your roof construction is a cold roof, not warm roof. There are lots of different methods and products to help manage cold roof ventilation. I've seen people put an internal layer of insulation on the inside of a cold roof ("hybrid roof" maybe?) and then fit window trickle vents or other approach to manage what you are describing.
On a cold roof...the more ventilation the better, The space above your insulation should be nearly at the same temperature as the great outdoors. It is amazing how dry an unheated air space will remain if well ventilated.
@@ooooobpbpbpooooo @geraldhenrickson7472 Thanks Just realized that this video is specifically for flat rooves - I think I must have been having an off day when I viewed this video - I was referring to pitched rooves. er sorry 😬😅
I'm a builder I know better it's so obvious to me😂😂😂😂, ffs get a grip it's not a building regs course. It's helping people with little knowledge out.. billy big balls👷🏼♂️.
Another way to look at it is, imagine if the celotex board was seen? You would make sure the scribing of the board is as neat as cutting in emultion paint between walls and ceilings. The outcome is an optimal thermal barrier, of such efficiency that your investment would be returned before the end of the 1st cold season. In other words, the time between your thermostat kicking in your heating system would be much much longer. We do this automatically by ensuring the front door is closed immediately after stepping in. Or we build a small porch around the front door, that also functions as a thermal barrier, alongside somewhere to put wet coats and shoes.
If you want to keep the roof space of a warm pitched roof open (like a loft) is it better to apply osb over the rafters, insulation over the osb and insulation beneath osb between the rafters? My thinking is the osb helps tie the roof together more, therefore increasing rigidity and also offering a safer way to work.
Yeah, very good point and it's just a different way of doing it definitely makes it more rigid however using the Superfoil this would've made the whole construction even deeper because you've had the thickness of extra battens so that the super quilt can fluff out
The first rule for stabilizing your inside climate is to prevent uncontrolled airflow. Think of any openings, cracks, voids, cutouts, windows and doors of course, vents, anything that faces outside the structure. Consider proper ventilation for void spaces inside walls, floors and roofs etc. Thing sshouldn't necceesarilybe completely sealed, you may need venting to prevent moisture buildup. Once your structure is tight and ventilated, insulation becomes a useful thing.
Hi Steve, I have installed a flat warm roof attached to my pitched cold roof. The airflow from the cold pitch roof has access to flow into the space between the joists of the flat roof underneath the 120mm insulation of the warm roof deck. Would I be need to install some insulation to the underside of the joist on my flat roof and still leave a gap for the airflow between the joist? I will be installing an airtight membrane, battens for services and then plasterboard.
yes you need to separate the warm roof from the cold roof thermally and air tightness. But keep the ventilation going on the vented side i.e. the cold roof.
@ thanks for the info. I have now installed 125mm insulation between the gap where the warm roof meets the cold roof. I’ve installed no insulation between the joists on the warm roof. I attached my airtight membrane and batons to the underside of the flat roof joists. Would it do any harm installing insulated plasterboard to the ceiling of the flat roof with say (25mm+12.5mm)? Thanks
I remember asking my roofer many years ago about gaps that I could see. He said you have to let the roof breathe. I asked what he meant and he said all roofs need to breathe, wood expands and contracts with tempurature. I just accepted his explanation at the time even though I thought privately that those gaps needed to be filled. Is there any truth to that? Or was I correct in my own assessment that the gaps should not be there?
Well, that's all wrong, isn't it? you can't have gaps that will let air movement in and out. It's like leaving the window open all year round in the winter you're gonna get cold aren't you? So what's the point of having heating on?
Thats sort of what I thought. He put vents underneath the fascias if I remember correctly but it didnt feel right to me. I thought those gaps should have been filled
Condensation damage is becoming more prevalent. Well insulated properties is ok but does come with risks if not built and operated properly. I rent out a well sealed timber framed property with forced ventilation. It was fine until one of my tenants switched off the ventilation as he didn’t like the noise. A year later when he over on I had structural damage. Cost me £’s to fix and not covered by insurance as considered negligence.
Thanks for your videos. Looking at the "tuck" area with the additional PIR, is foam enough to seal against vapour from leaking out between the PIR and the joist? Is there not a risk of Interstitial condensation somewhere between the warm side and the cold side?
It's a good question, but we never see that in fact if you think about the wall itself, the wall is very low in the way of air vapour control as it hasn't got a very good or no air vapour control layer at all and theoretically when we've tucked in, we're actually building part of the wall, not part of the ceiling.
I have a timber framed house. We have put wool in the walls, between floor joists and in the loft (cold roof). I am now adding Intello Plus to the walls which will extend into the loft. To help against thermal bridging I will be adding 40mm of woodfibre insulation board to the walls on top of the VCL and extending this up into the loft to the top if the rafters to tuck it in ;) It looks on this video like you extend the insulation up into the rafters but the insulation seems thicker when viewed from the outside. Is this because you are adding insulation above the wall plate?
I'm not quite sure What you're talking about. But yes, I have. I did a lot of insulation from the top of the wall plate to the insulation in the roof making everything airtime
Excellent advice! We just need to wean ourselves off of expanding foam and petrochemical based insulations now. Hard to do as they're so cheap (in comparison to natural insulation) and they have made them so easy to use too.
Could you combine the two? A foil backed insulation, with natural insulation (wrapped round it) to fill the gaps? I was surprised by the amount of foam insulation used there and thought that there must be a better solution. I know that there's gapotape, but it seems to be fairly expensive.
It's not just that the foam is cheap to buy the material; more important than that it's so fast to install. I think it's ease and speed of installation that keeps people using it: whether professional or DIY.
@@ricos1497 I'm not a great lover of PIR style insulation either but in roof construction I wouldn't consider anything else...It is sufficiently rigid to support the roof membrane and it is relatively impermiable to vapour. If you use fibre type insulation around the perimeter vapour can pass through it and at some point within the thickness of the insulation it will likely be cool enough for condensation to occur, making the insulation wet and in turn creating even more condensation as the trapped moisture makes the insulation less effective. This is also why Steve uses so much foam...it is to prevent any water vapour from travelling through the gaps around the insulation, as well as stopping air passing through from outside.
I'm still a bit confused :( What's to stop warm, humid area flowing into this "tucked" insulation and condensing when it passed the dewpoint ? I know that it's important to use a VCL below the main insulation to prevent problems with damp, so shouldn't we also use VCL at the sides ? Or is the argument that the cold face of the tucked insulation is exposed to the outside world, so that any trapped moisture can eventually escape before it causes problems ?
The first thing to take into consideration is that you will only get condensation when you have the right conditions i.e. a cold surface with warm air hitting therefore stopping the thermal bridging is a major key scenario and in this case there is no thermal bridging the weakest point here will be where the ends of the joists cross the top of the wall plate we have insulation between and we have wrapped the super quill over the top and around the outside everything is airtime if the end of the Timber Joyce gets cold that will have to transfer up through the 200×50 mm timber joist at least 150 to 200 mm to reach the inside as you know Timber is also a very good thermal insulator can you imagine having 200 mm of Timber wrapped around your building? How firmly efficient that would be so even though the timber joints are the weakest point? They are still extremely good and therefore you have to consider they are far from what you would call thermal bridging. Secondly, as regards, A air vapour control layer yes your air vapour control light should always be on the warm side of any insulation in our climate. And we had a good air vapour control layer in the roof construction as we wrap around to the wall we join to the air vapour control layer in the wall now surprisingly air vapour control layers in Walls, non-existent or extremely weak and the man-made materials used i.e. PIR insulation the foam and the super quill far greater than the vapour permeability of the walls conclusion no need to add a paper control control layer at this point as because the time you turn 90° you're actually forming part of a wall and not part of a roof. Question should be asked should we put better air vapour control layer in the walls? Answer is depends on all the other construction elements and if you have any kind of control of the internal environment as the moisture needs to go somewhere I know that's a weak answer but that goes into a whole different ballgame of conversation what we do now is that the method above works, especially in this application because of the size of the room, even though there is a kitchen below the relative humidity inside this room will be minimal. Air changes will be extensive because of size of the doors and also because of the living conditions of the family i.e. with kids running backward and doors open and shop move and management of internal airspace will basically work.
@@SteveRoofer thanks for the comprehensive reply, Steve. Makes sense ! As a lowly DIY'er, I'm slowly learning that the management of humidity in a building is an incredibly complicated subject... there are so many factors to think about. Really appreciate all time that you put into educating us :)
What would be the best way to insulate under rafters if the rafters were only 70 x 50mm and head height underneath was a premium - effectively a loft used for storage but at the top it was less than 5ft between floor and floor, would superquilt or something similar be better than nothing?
I made this mistake back in the eighties when i insulated the roof of a house i owned at the time. I didn't do this. In fairness I did get some noticeable benefit from the roof insulation. No doubt it would have been even better had i done it properly. I'm wondering now if any owner since I sold that house has noticed the problem😮
Hi Steve, loving the videos. I am learning quite a bit about vapour barriers and insulation. The only part that confuses me is where to vapour barrier the wall? I'm making a garden room with a warm roof where the osb for the roof will have a sticky vapour barrier applied on top, followed by insulation and then another later of osb on top as you explain in many of your videos. I will be tucking in the insulation in between the joists under the osb on top of the wall as you explain. My question is if i use a barrier on the inside of the wall and take this over the insulation between the joists (where it's been 'tucked'), what would i do about the joist? if i tape around the joints could there still be a dew point inside the joists themselves due to thermal bridging? will air movement pass through the joists (the wood itself) and pass laterally through the osb? is this even an issue I should be concerned about?
The vapour probability of walls is seen to be different than it is to a roof. Generally speaking, you have a lower vapour control system on a wall or in a lot of applications specially on extensions and old buildings there is no vapour control layer on the wall.
This is so helpful! Thank you so much! However, I really need your advice. I am preparing to convert the cold flat roof of my dormer to a warm roof. I am having a hard time finding details on a warm roof intersection with a pitched roof. Could you please share any advice you have around what happens around this intersecting junction. For instance, should the PIR be mitred to butt up against the pitched rafters or left hollow? And how should the rubber be tucked around the side of the flat roof at this junction. I would be eternally grateful if you could shed some light on this or even point me to some resources. Thank you!
All you have to do is make sure that the thermal element is continuous and as thick as all the other elements of insulation as you can sometimes you can't get it as thick but 25 mil is the minimum thickness that you wanna go to
When you've got a house that can't breath, do you leave the windows open to let the moisture out ? I have lot's of drafts in my old house, and it's nice and dry.
steve, how about a air flow through the timber part of the roof. ps; I see a lot of cavities are not covered with Fibre cement sheets to stop moisture going up in the roof space.
Okay I'm not quite sure of your question here but you've got thermal insulation on the roof when you get over the top of the wall you turn 90° and drop down if you've got this say 150 mil insulation on the roof that gives you a good quality turn go down try and keep 150 mil therefore you've got no way of having any kind of thermal bridging of course it's very hard to do but that's what you're trying to do. You then drop that 150 down to the top of the wall and stop because there's a wall there the wall isn't thermally that efficient probably however you've done the best you can. Should it be over the top of the cavity or on the internal wall? Well, it wants to be on the internal wall and extend outwards as far as you can so theoretically if you've got loads of insulation left over why not make it 200 mil wide why not go over the top of the cavity? The cavity should be closed at the top anyhow because you don't want warm moist coming up through the cavity into any cavities above where's Timber causing a problem? So do you need to do it irrelevant the main point to take away here is continuous insulation at the same thickness if you can achieve it and also air tightness.
Hi Steve, could you give me a bit of advice. I am building a garden room and the roof joist are 120 x 45(5x2). I was thinking of using(cold roof inside to out ) 12mm plasterboard - 1000guage polythene - 25mm PIR up to joist - 100mm XPS insulation between joists and 20mm air gap under decking with continuous soffit vents back and front. will I get problems only having 20mm air gap
1000 gauge polythene doesn't mean anything. It just means that it's a thick piece of plastic. You need to be using a proper a VLC not just polythene generally an air vapour control layer is coloured green as regards to the rest. It looks amazing if you're building a cold roof 20 mil is on the shallow side because obviously building control say 50 mil but you can take it up a little bit but 20 is a bit shallow personally I wouldn't do a cold roof. Try looking at some of the other roofing systems try looking at using super quilt.
Hi Steve Hope you can give me a little advice here! I am doing a warm flat roof using posijoist. I assume I can tuck in between the webbing and foam all the in-between areas? I also intend to extend the roof to firm a canopy of approx 1m. My architect has suggested we just extend the posijoists however will this not cause cold bridging? Any ideas on how I could form the canopy instead? Thanks in advance?
Great video Steve as always. Question's for you as a continuation to whats in the video. Would it be bad or good to fill the joists with extra insulation, and would you use an airtight membrane on underside of joist sealing back to the walls?
The golden rule is that you can put insulation between the joists on a warm roof, providing you only put one-third of the quality, the thermal quality of the insulation. No, you do not need a vapour barrier at that stage. No, you do not need to seal it against the walls at that stage, as you have sealed it against the walls higher up with the vapour barrier.
The answer is no what you Gotta think of is continuity of the thermal element on a piece of paper do a thick line across the ceiling. Where is the next thermal element? Do all the thermal elements join up to the walls up to the thermal element in the roof is there a break if there's a break? That's where your problem is
Air tightness and thermal bridge removal are critical for optimal energy efficiency, but you should not be doing this without mechanical ventilation to manage indoor humidity and air quality. For good airtightness, a continuous airtightness membrane is needed. You will have leakage between the joists and the wall in your example. Furthermore, exposed joist surfaces are thermal bridges. Insulate your joists as well.
Airtightness and thermal bridging are undoubtedly the most critical considerations here. In the example above, we have two layers fully bonded together, forming a continuous quilt of SuperFOIL. You really cannot achieve a more efficient, airtight, and unbroken quilt than what we’re installing here, close to 40 m² of unbroken thermal quilt. As with most projects, any potential breakdown will typically occur at the adjoining apartments. In this case, not only does the SuperFOIL wrap around the insulation at the ends of the joists, but we have also filled between the joists-traditionally a weak point. However, as you pointed out, the joists themselves are made of timber, which is actually a relatively good insulator. With the thermal insulation depth at around 150 mm, the exposed area of the joist is minimal, resulting in very little thermal bridging. Significant effort was put into ensuring airtightness was achieved at every stage. In fact, airtightness was accomplished with the first layer, and the second layer was installed assuming that the first might not be perfectly airtight. There is simply no way this could have been installed to be more airtight than it is now. Apart from the ends of the joists, everything is encapsulated with the same high-performing thermal material throughout.
The builder who was doing our infill extension mixed warm roof with the older style ventilated system, and I had to point out to him that cold air would come directly into his roof and sit in top of the plasterboard ceiling. He didn't understand but I got him to put insulation between the old and the new. Unfortunately, as I am not a builder I didn't see he hadn't done the outer parts that you have pointed out. When I get my flat roof redone, I've a good mind to get the warm roof converted to the match the rest of the flat roof and fix the problems his roof has introduced. The other issue is the existing original flat roof slopes, and the warm roof is flat and sits proud of the old roof. It has leaked and causes the rain water to be directed to one side of the sloped part and now overwhelms the gutters. I fixed the leak as he was blaming the old roof and didn't accept responsibility for his poor work, so I wanted nothing more to do with him, but I wish I had known what you have pointed out. Oh well, lesson learned and thanks for posting.
@@pauldavies7251a warm roof?? What are you blabbering on about! A roof and attic are hot in summer cold in winter. If you seal a home up with no air flow, it causes moister to condense and cause black mold. And in worse case if you use natural gas cooking you could end up with high levels of carbon monoxide build up! You insulate the FLOOR of the attic, and allow the roof to “breath” and release moisture from the building walls.
@@martinbuss6818it’s a warm roof. The space between the joists is effectively inside the room. Moisture won’t condense inside. There is a vapour barrier above, then 120mm of celotex. You don’t need ventilation in a warm roof.
@@martinbuss6818 I love the arrogance from clueless people 🤦♂️🤐 , A warm roof means the insulation goes outside the main roof so there's absolutely no need for ventilation, You only need ventilation when you've insulated between joists or rafters, Aka "cold roof"
In this video, I am forming a wall roof. Warm roofs do not need to be ventilated. cold roofs need ventilating. This video is only about warm roofs that do not need ventilating. In the video, I show that I go around the edges and insulate and make it completely airtight. The insulation around the edges meets the insulation on the roof. Theoretically, you could sit in the room without a ceiling and still be warm.
@@SteveRoofer It’s not just about the roof space. It’s the whole house. Houses get used by people. Damp from breath, use of water, drying clothes, etc.. That moisture has to go somewhere & usually ends up around windows & cold walls. Sealed buildings require active ventilation to remove the moisture from the air, preferably in combination with a heat exchanger. I’ve had plenty of cases where condensation is a problem for cold roof spaces too, but warm roofs have become a regular occurrence in the last 4 years with both new build & reroofed extensions. In a ventilated cold roof, there is a wicking action for some moisture to escape through the ceiling &, although when done incorrectly, adds to the condensation issues, a properly installed cold roof or a warm roof with active ventilation will significantly reduce the possibility of condensation issues for your clients.
After reading many of the comments on this video, it seems many folks do not understand that of the two approaches to roof insulation, you are speaking only to how to properly create a "warm roof" as opposed to a "cold roof". Everyone wants a properly insulated ceiling inside yet their are two distinct ways to achieve such. If a homeowner or contractor creates some abomination sharing the worst features of both methods...havoc can and likely will ensue. Thanks for the video.
no because there is no airflow it's a completely sealed unit just like your house you don't have to have airflow around your kitchen table. All the timbers you see in this video the joists are all internal.
Hi Steve, I'm just in the process of replacing my old cold flat roof extension, it runs to the centre with a central gutter. Im fitting a wall plate and having it slope all away from the hoise with new joists above the old. A few questions, can the existing felted but non insulated roof be left in situ or can this cause problems with damp. Im intending to put 150mm PIR between the new 200mm joists, leaving a 50mm air gap, followed by a quilted foil over the top of the joists, 50mm battons then 18mm 0SB3 followed by EPDM. Will this cause any problems, im planning to let air flow across the width of the roof via the gap in the battons above the foil layer. The existing roof had no insulation in the original 225mm cavity and is finished with polystyrene backed plasterboard. I understand i will need to expose the ends of the old roof to continue the new roof insulation to the existing brickwork. Thanks in advance Jonathan
Thermal insulation is considered outside of the construction of the building and there is no thermal bridging therefore there wouldn't be no need for ventilation.
Moved into our bungalow with rafter level insulation that was freezing - a massively shoddy job - dropped all the insulation to ceiling level and doubled the thickness - worked this out inadvertently 😮
@@ooooobpbpbpooooo the soffits were already ventilating the ceiling so now the air goes up and out through the roof vents instead - one part of the house was already done like this so it’s not clear why they chose to go warm roof on the main part without doing it properly 🤷♂️
Get ready for the 'builders' and 'roofers' who say you need to keep these areas open for air flow. Those guys are absolutely clueless. Have no idea about warm and cold roof sysyems.
@SteveRoofer You mention in the video at 6:25 that this construction does not have a lower deck. I heard the lower deck with OSB is a liability in warm roofs. OSB's glue makes it near non breathable and as such prevents moist air from reaching the top of the insulation and condensate there, eventually leading to the OSB rotting. Do you have thoughts and is there up to date best practices documented about this?
This is a warm pitched roof, not a warm flat roof however it performs exactly the same way and an air control layer should always be at the very bottom so to answer your question yes OSB decking is actually a very good air the controller it's actually in the correct place because on top of it you're gonna put an even better air vapour controller. I think most of the point is when you put OSB on the top of a warm roof. We see that rock an awful lot of the time and a lot of people say you shouldn't do it. I had this conversation with one of my contractors and between him and me we have been doing it for the last 15 years with no problems, but that could be because we use a very good air vapour controller so the sandwich of materials is completely sealed and we don't get a problem.
@@SteveRoofer thanks for your reply. I was thinking about using something like Stamisol DW on top of the insulation, breathable out, waterproof but advertised as offering structural benefits (in fact the only reason why I would be tempted by OSB - or if seeking that benefit plywood seems like a better choice?). I have no OSB specified in my upcoming warm pitched roof at ALL, just VCL/Tissue facing PIR Insulation/Breather/Battens/Counter and Tiles. Do you think a lower OSB deck is absolutely necessary for structural reasons?
What's the depth of the pieces of ENERTHERM between the rafters meeting the soffit side please? Where does the air breather membrane go? is it already on the other outer side of the insulation? Do you place the vapour control layer on after the insulation is put up then follow with the plasterboard? Thank you:)
okay? First of all the super quote used here is also an air vapour controller so when you're looking up from the bottom you've got an air vapour controller already installed in the correct place. We haven't used any PIR insulation on this roof what you're looking at in the video is the underside of the, super quilt between the joists we will be installing 200 mm of Rockwall. This buildup gives us the correct UValue for building control.
Great video! Can this be done retrospectively? i.e. remove fascia board from the outside and seal it up from there without having to re-roof? Thank you.
Pretty much the same way as we are doing above you're either gonna do cold roof construction or warm roof construction and you're gonna look after the ventilation and the thermal point correctly it's all doable. It's all just down to detailing.
no because you don't have your kitchen table or your kitchen units wrong and all the wood that you're looking at is internal just like your kitchen table and that's because you control the internal environment
You're right it shouldn't be a soffit then on a warm roof if you're referring to this roof it's because there's a cold roof fitted over the top of the warm roof
@baldyslapnut. I can guarantee that at some point water or moisture will get into that warm roof at some point. the home owner will have zero idea its happening until the rot is obvious. it's the same scam as spraying your roof with insulation that mortgage companies are demanding it's removed. it's the same scam as cavity insulation. you need to be able to inspect wood for any problems. sealing everything up to save a couple of degrees is really not worth it.
perhaps moisture will get into the roof, but the thing is is that it's fully vented above for it to get out. It's also got the highest quality air vapour control at the bottom so if Var does get into it from below and the only way it would do is because it would go through the air control layer which is supposed to do but as it's a control layer it controls the amount gaining because the amount getting in is controlled to a point that more can get out above you don't get a buildup because you don't get a buildup. You don't get a problem not only there moisture on its own. It's not necessarily a problem. It's only a problem when it hits something cold and condenses i.e. cold bridging as there's no possibility of cold bridging in this roof therefore there's no chance that the moisture can turn into water and cause a problem it's just physics.
This is one of the most intuitive comments really thinking of what happens in the future and you've actually answered the question that most people do not understand lots of people ask me why I'm against the cold roof construction and the simple reason is because of the amount of insulation that we are now using you have taken away the drying ability of the heat loss. This drying ability will definitely make a difference to any product above. Take it away and you could have problems such as the lifespan of anything like tiles, buttons fixings and so on on this particular job we are using plastic slates but they are still on wood with galvanised nails so without the rising heat just how long will this last? Get back to me in about 20 years time, and I'll tell you how it goes!
That depends on your loft if the loft is a cold area as long as you keep the ventilator ventilation and move the air up there you won't have a problem.
I’m confused, I thought a warm roof meant insulation would go on TOP of the decking. This looks like insulation is immediately below the decking. Help me out, what am I missing?
Correct, the insulation should sit on top of the decking which has a layer of felt tacked to it and a 3 layer of polyester membrane torched on top of insulation. A thirty year life. Just one point though, it is not possible to acquire a underwritten 20 year warranty for a F/G or rubber roof?
Thanks again Rob, you're correct looking through some of these replies I can see lots of people are confused warm roofs do not need ventilation cold roofs need ventilation
Thanks, rob, I see you are answering a lot of people for me. This video has got quite a lot of his quite quickly. I need the help. I can't answer them all. I can't believe the amount of people that do not understand why roofs don't need ventilation
@@SteveRoofer I'm a Chippie, been in the trade for 30 years, build loads of warm deck pitched and flat roofs, on lofts/extensions. I've learned that many, many people really haven't the faintest idea how, when and why roofs need or don't need ventilation, There is a huge amount of information available on the subject if only people would take the time to research it rather than blindly harping on about ventilation!..all the best.
We built an extension and put insulation between the joists but it wasn't on the drawing, the architect didn't think of it, so it's not necessarily the tradesmans fault
In this video, I am forming a wall roof. Warm roofs do not need to be ventilated. cold roofs need ventilating. This video is only about warm roofs that do not need ventilating. In the video, I show that I go around the edges and insulate and make it completely airtight. The insulation around the edges meets the insulation on the roof. Theoretically, you could sit in the room without a ceiling and still be warm.
I believe depends where the dew point is. If the insulation is airtight and thick enough no moisture reaches the outer wall or condenses in the middle of the insulation.
In this video, I am forming a wall roof. Warm roofs do not need to be ventilated. cold roofs need ventilating. This video is only about warm roofs that do not need ventilating. In the video, I show that I go around the edges and insulate and make it completely airtight. The insulation around the edges meets the insulation on the roof. Theoretically, you could sit in the room without a ceiling and still be warm.
Nice neat block work! Your lucky if you find any of them filled in by any trade. Only time that would happen without getting you guys in,is on the tradesman doing his own work!
Hi Steve, very informative, thanks for posting. I want to replace the polycarb roof on my 3m sq lean to conservatory. Would you recommend a warm or cold roof? Just worried about the weight of a warm roof. Also what thickness joists would you use on a small roof like mine? Cheers.
I'm having an extension built at the moment and they haven't insulated behind the fascias. The problem is there is now a very small gap between the joist and the parallel wall and very little space to get anything in - the only thing I can think of is expanding foam. Any advice?
Brilliant to see this and at just the right time. We have some real challenges with how our roof has been left on our build. We had a warm flat roof joining a cold roof and one was open to the other. We have closed the junctions tightly with PIR and then painted all of the joints and gaps with passive purple. Even without the build finished we could tell a massive difference. We have a bigger challenge on the eaves of a cold vaulted celiling where the roof PIR was simply no where near joining up with the wall insulation. Would really like your opinion on how to tackle it.
@@SteveRoofer Thanks so much for your amazing support. We have found your channel so so useful and your responses to our questions so quickly were such a help. Your points about trades not wanting to spend time doing the right thing are so crucial. Sadly I don't think many general builders are even aware of what they should be doing. The quality of our build in this respect was very poor.
Good question and the answer is yes it is to quite a high point so realistically when assessing where you're using it you can assess whether or not you need to add further vapour control controls generally speaking. You don't need to add a high vapour control on a vertical wall, although you do need to have some kind of vapour control and the PIR insulation and foam is efficient
5:40 I think lots more water vapour will get into the PIR through the cut end than through the bigger silver sides and make it damp and useless ... Its like when you have a lot of broken windows mending one doesnt make any difference but when you mend the last one suddenly the house is warmer and less window (actually the one before last cuts the winds) I'm planning on wrapping my kingspan seconds in membrane like a xmas present and taping it up, any great reason not use any old vapour barrier and tape from Wickes or Toolsation compared with the most expensive sticky packed stuff?
but they get damp through the cut ends if left in the rain and take weeks to dry out .... and vapour is smuch smaller than rain molecules @@pauldavies7251
Hi Steve I'd love you to look at my loft space, condensation everywhere. Discoloured insulation. I think our soffits are being covered up with insulation. House builders have washed their hands of it, marley risk have rejected our claim. Scandalous behaviour!
Thats because moisture condenses on the cold sheathing & gets trapped by the insulation with no way to dry out. To address it, an air permeable insulation (no foil) and dehumidification is needed. The dehumidifier will reduce the amount of moisture that condenses, and a permeable insulation will allow condensate to evaporate (ie when the roof become warm when the sun hits it. The foil membrane traps moisture in. Rockwool (Roxul) is a moisture permeable insulation. Another option is to use a permeable roofing membrane that allows trapped moisture to escape from the topside of the roof, but you need a roofing configuration has an air gap so for the permeable membrane to work: ie metal, slate, tile roof with lathing set up to draw in air from the soffit up through the ridge cap. Building science {dot} com has a collection of articles about condensation issues in well insulated homes. They did a lot of experiments to test what did & did not work. You can read them for free.
Hello. I have a 70’s house, typical brick construction with cavity walls. Where the joists meet the wall there are inch gaps into the cavity. Should these be filled? Also on one side of the house I have an attached (unheated) garage. The joists for the garage flat roof go into the outside leaf of the house cavity wall, again with a gap. Also fill? I feel it’s highly likely that cold air from the garage (and loft) goes into the (filled with fluff) cavity and would make its way into the house.
You have to be careful insulated older homes, as it can lead to rot. What happens in a lot of older homes that have insulation upgrades, is that moisture gets trapped by the insulation & condenses on the cold sheating & joists. Over time they start to rot. Because the older homes aren't insulated & have a lot of air movement, any moisture that does condense quickly evaporates. What you probably need to do is first get keep your indoor humidity low with a whole house dehumidfier, upgrade your bathroom fans (make sure they work) to pull out bathroom moisture. ideally a Timer on the fan switch is ideal because you can set it and not have to manually turn it off (reason why most people don't use them). And then test a second of your home to see if moisture accumulates. (ie test a section of your home) You need to use a removable insulation such as rockwool. I don't recommend spray foam since you cannot inspect behind it to see if there is a condensation problem.
Thanks, yes I've started with rockwool in the inch gap and then foil tape over the hole on the garage side so far. In the garage it's easily accessible, on the house side it's not because obviously it's in the ceiling space. I think the garage side is lowest risk because the other side of the house (identical except no garage) has no gaps as it's an outside wall. I have zero signs of damp as of now, but will be something I keep a close eye on. I think it is as modern/good as is possible for 1970, pretty square and overengineered. I have over fascia ventilation in my loft in preparation for doing as much insulation as possible up there. @@guytech7310
Tucking in, as you put it, would that not cause an issue with warm air being trapped inside? Are you not meant to have ventilation from one side to the other? Not being arsey, genuinely not sure lol
What’s the best way to rectify this cost effectively? Do you have to remove the ceiling from the inside? Can you do it from the outside by removing the fascia board?
You can do it in many ways. Obviously, you choose the cheapest way if that means taking ceilings down inside or taking gutters and facias off outside or cutting down from up above Whatever way you need to do it.
Hi Steve, I see below that you have spoke about warm roof and cold roof but my question is, BC (sorry for swearing) have said I MUST have ventilation installed throughout the roof to allow for airflow from the outside through the roof. I have a 150mm joist and I have to use 100mm insulation. Would I be right in thinking I could install the insulation 30mm of the roof lining and this will leave a 20mm gap from the insulation to the wall which I could then fill with insulation, allowing me to "wrap the room" whilst also allowing the ventilation above the insulation for the BC approval?
Hi Steve. Building out a flat roof on a garden room at he moment. warm roof. Is there any point in putting timbers in now ime noggins allowing for the insulation or wait till after ?
Impossible to have condensation inside the insulation, there's a major problem if you have, Cold roof you need to worry about ventilation between insulation & roof deck
This is perfect timing, I've just built a warm roof, tied into my houses pitched cold roof. Now the joist void under the warm roof is open into the pitched roof loft space. On the inside Should I close this off?
If the pitched roof is vented i.e. a cold roof, then you've got to stop all that cold air getting into the area between the choice of the warm roof. So yes seal it off
When roof manufacturer's produce specifications for warm roofs they don't include this and it does often get missed. At a minimum you want as much insulation as there is in the wall.
Hi Steven. How do you ventilate a loft conversion properly when you have a warm deck flat roof box dormer on one side and on the other you have vaulted rafters which are insulated in between then insulated over them underneath? Cheers
Ridge vents or high level tile vents sufficient to provide at least the equivalent of a continuous 10mm gap....so for a 6m long ridge you would need vents with a total clear vent area of 60,000mm2. You will also need a means of making sure every rafter void is vented by whatever vents you install (so continuous ridge vents, vent tile every rafter or create a vent path at the apex of the roof by providing a flat insulated ceiling just below the ridge, and using the small void above to link the rafters)
Useful videos. I have a question for a small shed/office I'm rebuilding with a cold roof. Have plenty of space between roof joists for insulation, and space above for ventilation. However, due to being on boundary line there's only a sizeable overhang on the front of the building. Obviously easy to add vents to the soffit at the front - what to do at the rear to help air circulate? Is it possible to get vertical venting that could be fitted at different points along the facia board? Have seen mushroom vents which could enable air to escape upwards, but would prefer to vent straight out the back with less possibility for leaks if possible. Any suggestions or advice welcome.
If it's only a part time she'd office it's not as important to fully vent it as there won't be much condensation build up compared to a kitchen or bathroom where there's heavy use with multiple people & cooking & steam from shower
This is always a problem in a cold roof but it's not a problem in a warm roof. One of the reasons we don't do cold risk is because of this problem and the problem of thermal bridging
Wow, thank you! The response to this video has been quite amazing. I didn't actually want to post it. I had it in my bin for quite some time thinking that I would never publish it. However, a customer asked me a question, and I sent it to him as a private video; he thought it was amazing and suggested that I put it up, so I did, and it's probably going to be one of my top performing videos. Thanks for your vote
Please understand that this is a warm roof and do your research before attempting this. If this was a standard cold roof, doing this insulation like that would be wrong.
well you shouldn't be putting a DMP on top of the roof. You should be putting a roof membrane on top of the roof if you put the zips panels on correctly i.e. no gaps cause that's the big problem with sips and no thermal bridging. Between the panels as they joined together and also an air vapour control layer at the bottom then it's a warmer and you don't need to invent it.
@SteveRoofer sorry, I did actually mean EDPM (diy getting terminology wrong). Panels didn't go amazingly well together, but I foamed and taped any gaps between osb with buytle tapw, and put up vapoour barrier the way you explain with tape etc on underside
@@SteveRoofer Hi Steve, wouldn't there be cold bridging from where the rafters overhang the wall plate to the outside? i.e. the part that the fascia board would normally be nailed onto?
The cold ends of the joists are fully ventilated by the outside air and will be at outside air temperature or very slightly warmer so no condensation can take place.
As a former Building Control surveyor this was such a common issue, both on new extensions, replacement flat roofs, and even on large new housing developments. On domestic work I would probably say this simple point was missed getting on for 50% of the jobs that I saw at this stage. The issue is that many builders build the walls as they always did with ventilated cold roofs, stopping the walls at plate height. This also applied to the walls parallel to the joists leaving an uninsulated void between the top of the wall, the deck and the joists either side, with only at best a 25mm gap to get the insulation into the void when the issue was pointed out. It really isnt good enough to just fill up the space with quilt as this can create condensation issues, it really needs to be PIR as Steve shows here foamed into place. Another important factor when upgrading a ventilated cold roof to a warm roof is that you need to remove all the old roof insulation from between the existing joists, leaving it in place, particularly if there is a good thickness, means that the vapour barrier under the new insulation will not be at room temperature and can cause condensation problems that the warm roof was designed to overcome.
Yes you are absolutely right 50% though I think is low I'd say 95% of everything I see they haven't done it correctly. Your point about leaving insulation between the joists if you are converting from a cold roof to a warm roof is also totally correct. Personally, I like to go on a rule of thumb 2/3 of the thermal insulation must be above the air vapour control layer to therefore assessment needs to be made about how much insulation is left below if it is old fluffy stuff it's probably not that good so it can stay there if however it's more substantial and well fitted then it may have to be removed.
We bought a house and the previous owner was really proud of the money he'd spent on insulation. We'd have bought the house regardless, but after we bought it I realised he'd wasted his money because the people who had installed it had left big gaps which allowed airflow.
We're slowly working on it ourselves now, but this video was great as it showed me I was right about the issues, and my approach has been more or less correct, too. Thank you!
Thank you very much for the comments this is the problem I'm finding so many insulated properties even new builds that haven't been insulated correctly.
@@SteveRoofer There's an awful lot of folks that think they know what they're doing, but lack the critical skills to look at it and see the obvious issues. And of course, they don't bother to check up on the latest info or anything. "This is the way I've been doing it for a decade." And of course the, "That'll do," mentality.
Thanks Steve for taking the time to put these vids out. They are invaluable to all homeowners.
Glad you like them!
Wish I'd seen your advice years back. Educating people on how to do it right no matter the cost is always worth it. But everyone wants it done cheap and fast.
Unfortunately, that's the way of the world
Don’t believe majority of customers want cheap and fast. Builders however yes despite customers paying for a proper job and when it’s finished don’t know if it’s been done properly.
We had new extension done few years ago using the warm room method and they didn’t fill the gap with insulation between joists, our new extension was absolutely freezing in the winter. I showed the builder your video on thermal bridging and they took the fascia board down and corrected it and now it feels warm and cozy. Thanks for these educational videos
And he he did all that within 18 hrs of this video being posted?
@@Christopher-zt9eu Steve said in the video that he posted a video about ten years ago.
@@Christopher-zt9euposted a video 11 years ago, which viewed by 475k people so far
Your all in front of me I don't think I have posted the link to that video ill have to go and do it
warm roof have insulation on the out side, you don't need to do anything on the inside
Dear steve et Al. I have just pulled 1500 kg of lead off my annexe which after 20 years was like a burst sofa. It was laid on a warm roof done badly with no vapour barrier. I have stripped it and used Allutrix then put Res Tech flexible fibreglass over the new deck. Vapour barrier and thermal bridging control is critical when working on modern roof systems. Thanks for a very good video.
you wanna weigh that lead in you got a payday right there!
If you completely seal up roofs like that the timber will rot out double quick . Sealing everything up causes all sorts of problems and we leave air gaps on purpose you will cause mould, condensation and damp .
Interesting point, I to have been wracking my brains about how to insulate effectively without trapping moisture, I have tried to strike a balance but its difficult to avoid condensation finding cold unventilated areas. Problem seems to be that we won't find out for 10 years if it's going rotten!
@@jonwilmot5331 we know that not using Vapor barriers and ventilation timbers go rotten that’s why we ventilate loft spaces , bathrooms, flat roofs and put vents on double glazed windows.
Enough roof tile vents should suffice
@@springy2670quite tricky on a flat roof 🤣
@@dragonfitter Then you should have put some vents in the lantern you've clearly installed on your flat roof 😉😘
When we built our lofty on a 3 bed semi we spent ages and a lot of money insulating the roof and walls and getting obsesive about draught proofing. In the last three years since we have never turned on the reads up here, the loft stays very cosy all winter with just the heat leaking up from downstairs. To be fair though you do need a forward looking customer to agree the extra costs involved in getting it right, done well though a few years of reduced heating bills and you have paid for it. Good video, thank you.
yes you are absolutely right. It's costly and fiddly and finding the right people to do the work it's always a problem
Did I read somewhere that you been a flow of air in the foot area to prevent moisture build up and mold - which is why soffit boards have holes in them to allow for breathing?
Soffit boards have holes if you need the ventilation between where you’ve insulated and the outside world. Typically a cold roof. What Steve is demonstrating here is warm roof design where you are creating the thermal envelope around the end of the soffit. Moisture in buildings is typically caused by warmer moist aire hitting something that is colder and the coldness is below the dew point for the warm humid air causing the water vapour to condense and turn in to water on the colder surface. If this is wood then you have the ideal environment for mould and rot. Because it’s hidden behind plasterboard or something else you don’t realise until it’s starting to show up which is too late and big bills are due.
Thanks Steve, great vid as always. I think what you have to remember is warm air is attracted to cold air, so if you have these tight gaps the air fairly whistles out. It would be interesting to compare say 18mm ply totally sealed at the edges with insulation with gaps in that area.
Years ago we had a kitchen done with a warm roof, the builders did a horrendous job, large gaps, they blocked roof vents because they couldn't be bothered to trim them down, it was so bad I took it down and redid it. Reading a few comments here, it seems that most of the mistakes are down to builders, the so called professionals! Hence why I do most things myself, if you want something doing correctly do it yourself.
Yes, I agree most of the time I see very good work undertaken by people who own their own properties.
Thanks for the info. Had a flat roof extension done last year and it saddens me that i know for a fact this tucking in was NOT done. So this summer it’s fascia’s off and do it properly … Myself 😢
Yes, unfortunately, that seems to be the way do it yourself
I thought that you had to leave a space where the ceiling insulation meets the soffit for ventilation of air to be able to get in and stop roof condensation?
warm roofs, do not have ventilation. You must be thinking of a cold
Have you got a video that shows the difference between the two?@@SteveRoofer
No worries I found one.
So did I. There is no mention of condensation or mould !
The moisture in air condenses where warm moist air contacts a cold surface. Hence if the roof structure is fully insulated without cold air ingress or cold bridging, the moisture won't condense as the insulation internal face is at or close to the ambient air temp.
Very good video Steve. Thanks for the info. I always thought (or think I was told when I did my Carpentry & Joinery course between '94-'97) that you had to leave a gap between floorboards for air to circulate. I guess this has now been superseded in today's world? Thanks once again and ATB
its different a roof level
@@SteveRoofer Aah, of course! Thanks for clarifying Steve. ATB
Hi. Interesting video. But perhaps you could do another to clear up some confusion. Especially for owner of older houses that require ventilation in their rooves to stop condensation. I have tried this method with my new roof and quickly discovered that the roof needed air movement yet I still would like to be able to some how seal out the cold air from out side getting into the inner space on the other side of the insulation. How do we do that?
If it requires ventilation, and is an older property, I'm assuming your roof construction is a cold roof, not warm roof. There are lots of different methods and products to help manage cold roof ventilation. I've seen people put an internal layer of insulation on the inside of a cold roof ("hybrid roof" maybe?) and then fit window trickle vents or other approach to manage what you are describing.
On a cold roof...the more ventilation the better, The space above your insulation should be nearly at the same temperature as the great outdoors. It is amazing how dry an unheated air space will remain if well ventilated.
@@ooooobpbpbpooooo
@geraldhenrickson7472 Thanks Just realized that this video is specifically for flat rooves - I think I must have been having an off day when I viewed this video - I was referring to pitched rooves. er sorry 😬😅
Im a builder and youre stating the obvious( to me). I always fit 2 x 100 mm layers between the joists at that location. Blindingly obvious.
yes, but you're obviously a builder with a brain I can't believe what some people do it's just no thought in the process
I'm a builder I know better it's so obvious to me😂😂😂😂, ffs get a grip it's not a building regs course. It's helping people with little knowledge out.. billy big balls👷🏼♂️.
Another way to look at it is, imagine if the celotex board was seen?
You would make sure the scribing of the board is as neat as cutting in emultion paint between walls and ceilings.
The outcome is an optimal thermal barrier, of such efficiency that your investment would be returned before the end of the 1st cold season.
In other words, the time between your thermostat kicking in your heating system would be much much longer.
We do this automatically by ensuring the front door is closed immediately after stepping in.
Or we build a small porch around the front door, that also functions as a thermal barrier, alongside somewhere to put wet coats and shoes.
The interesting thing with this is that you need to take time to get it right and it will pay back. Get it wrong and you've just wasted your time.
If you want to keep the roof space of a warm pitched roof open (like a loft) is it better to apply osb over the rafters, insulation over the osb and insulation beneath osb between the rafters? My thinking is the osb helps tie the roof together more, therefore increasing rigidity and also offering a safer way to work.
Yeah, very good point and it's just a different way of doing it definitely makes it more rigid however using the Superfoil this would've made the whole construction even deeper because you've had the thickness of extra battens so that the super quilt can fluff out
Totally agree with you Steve, I see this to often as some trades don't care? 😖😖
I do as you do as it's the only way to do it properly 👌👌
Cheers
Well said!
The first rule for stabilizing your inside climate is to prevent uncontrolled airflow. Think of any openings, cracks, voids, cutouts, windows and doors of course, vents, anything that faces outside the structure.
Consider proper ventilation for void spaces inside walls, floors and roofs etc. Thing sshouldn't necceesarilybe completely sealed, you may need venting to prevent moisture buildup.
Once your structure is tight and ventilated, insulation becomes a useful thing.
Yes, this is all true
Hi Steve, I have installed a flat warm roof attached to my pitched cold roof. The airflow from the cold pitch roof has access to flow into the space between the joists of the flat roof underneath the 120mm insulation of the warm roof deck. Would I be need to install some insulation to the underside of the joist on my flat roof and still leave a gap for the airflow between the joist? I will be installing an airtight membrane, battens for services and then plasterboard.
yes you need to separate the warm roof from the cold roof thermally and air tightness. But keep the ventilation going on the vented side i.e. the cold roof.
@ thanks for the info. I have now installed 125mm insulation between the gap where the warm roof meets the cold roof. I’ve installed no insulation between the joists on the warm roof. I attached my airtight membrane and batons to the underside of the flat roof joists. Would it do any harm installing insulated plasterboard to the ceiling of the flat roof with say (25mm+12.5mm)? Thanks
I remember asking my roofer many years ago about gaps that I could see.
He said you have to let the roof breathe.
I asked what he meant and he said all roofs need to breathe, wood expands and contracts with tempurature.
I just accepted his explanation at the time even though I thought privately that those gaps needed to be filled.
Is there any truth to that? Or was I correct in my own assessment that the gaps should not be there?
Well, that's all wrong, isn't it? you can't have gaps that will let air movement in and out. It's like leaving the window open all year round in the winter you're gonna get cold aren't you? So what's the point of having heating on?
Thats sort of what I thought.
He put vents underneath the fascias if I remember correctly but it didnt feel right to me.
I thought those gaps should have been filled
Condensation damage is becoming more prevalent. Well insulated properties is ok but does come with risks if not built and operated properly.
I rent out a well sealed timber framed property with forced ventilation. It was fine until one of my tenants switched off the ventilation as he didn’t like the noise. A year later when he over on I had structural damage. Cost me £’s to fix and not covered by insurance as considered negligence.
Yes, without a doubt you need to control the internal environment or this can all go pair shaped
Thanks Steve Roofer! I'm looking to build a workshop and this will be excellent!
Fantastic!
Thanks for your videos. Looking at the "tuck" area with the additional PIR, is foam enough to seal against vapour from leaking out between the PIR and the joist? Is there not a risk of Interstitial condensation somewhere between the warm side and the cold side?
It's a good question, but we never see that in fact if you think about the wall itself, the wall is very low in the way of air vapour control as it hasn't got a very good or no air vapour control layer at all and theoretically when we've tucked in, we're actually building part of the wall, not part of the ceiling.
I have a timber framed house. We have put wool in the walls, between floor joists and in the loft (cold roof). I am now adding Intello Plus to the walls which will extend into the loft. To help against thermal bridging I will be adding 40mm of woodfibre insulation board to the walls on top of the VCL and extending this up into the loft to the top if the rafters to tuck it in ;) It looks on this video like you extend the insulation up into the rafters but the insulation seems thicker when viewed from the outside. Is this because you are adding insulation above the wall plate?
I'm not quite sure What you're talking about. But yes, I have. I did a lot of insulation from the top of the wall plate to the insulation in the roof making everything airtime
Excellent advice! We just need to wean ourselves off of expanding foam and petrochemical based insulations now. Hard to do as they're so cheap (in comparison to natural insulation) and they have made them so easy to use too.
Could you combine the two? A foil backed insulation, with natural insulation (wrapped round it) to fill the gaps? I was surprised by the amount of foam insulation used there and thought that there must be a better solution. I know that there's gapotape, but it seems to be fairly expensive.
I think the way to go is to use multi foil insulation. There's a company called super foil out there. All of these foils are much better
It's not just that the foam is cheap to buy the material; more important than that it's so fast to install. I think it's ease and speed of installation that keeps people using it: whether professional or DIY.
@@ricos1497 I'm not a great lover of PIR style insulation either but in roof construction I wouldn't consider anything else...It is sufficiently rigid to support the roof membrane and it is relatively impermiable to vapour. If you use fibre type insulation around the perimeter vapour can pass through it and at some point within the thickness of the insulation it will likely be cool enough for condensation to occur, making the insulation wet and in turn creating even more condensation as the trapped moisture makes the insulation less effective. This is also why Steve uses so much foam...it is to prevent any water vapour from travelling through the gaps around the insulation, as well as stopping air passing through from outside.
I'm still a bit confused :( What's to stop warm, humid area flowing into this "tucked" insulation and condensing when it passed the dewpoint ? I know that it's important to use a VCL below the main insulation to prevent problems with damp, so shouldn't we also use VCL at the sides ? Or is the argument that the cold face of the tucked insulation is exposed to the outside world, so that any trapped moisture can eventually escape before it causes problems ?
The first thing to take into consideration is that you will only get condensation when you have the right conditions i.e. a cold surface with warm air hitting therefore stopping the thermal bridging is a major key scenario and in this case there is no thermal bridging the weakest point here will be where the ends of the joists cross the top of the wall plate we have insulation between and we have wrapped the super quill over the top and around the outside everything is airtime if the end of the Timber Joyce gets cold that will have to transfer up through the 200×50 mm timber joist at least 150 to 200 mm to reach the inside as you know Timber is also a very good thermal insulator can you imagine having 200 mm of Timber wrapped around your building? How firmly efficient that would be so even though the timber joints are the weakest point? They are still extremely good and therefore you have to consider they are far from what you would call thermal bridging. Secondly, as regards, A air vapour control layer yes your air vapour control light should always be on the warm side of any insulation in our climate. And we had a good air vapour control layer in the roof construction as we wrap around to the wall we join to the air vapour control layer in the wall now surprisingly air vapour control layers in Walls, non-existent or extremely weak and the man-made materials used i.e. PIR insulation the foam and the super quill far greater than the vapour permeability of the walls conclusion no need to add a paper control control layer at this point as because the time you turn 90° you're actually forming part of a wall and not part of a roof. Question should be asked should we put better air vapour control layer in the walls? Answer is depends on all the other construction elements and if you have any kind of control of the internal environment as the moisture needs to go somewhere I know that's a weak answer but that goes into a whole different ballgame of conversation what we do now is that the method above works, especially in this application because of the size of the room, even though there is a kitchen below the relative humidity inside this room will be minimal. Air changes will be extensive because of size of the doors and also because of the living conditions of the family i.e. with kids running backward and doors open and shop move and management of internal airspace will basically work.
@@SteveRoofer thanks for the comprehensive reply, Steve. Makes sense ! As a lowly DIY'er, I'm slowly learning that the management of humidity in a building is an incredibly complicated subject... there are so many factors to think about. Really appreciate all time that you put into educating us :)
What would be the best way to insulate under rafters if the rafters were only 70 x 50mm and head height underneath was a premium - effectively a loft used for storage but at the top it was less than 5ft between floor and floor, would superquilt or something similar be better than nothing?
What's a very long question which really there isn't any answers because it's just not a big enough size to do it properly.
What about pitched cold roofs? Should you be taking the insulation all the way to the eaves/soffits allowing for 50mm air gap?
yes absolutely take it right across to the soffit but don't stop the ventilation if the ventilation is coming from the soffit boards
I made this mistake back in the eighties when i insulated the roof of a house i owned at the time. I didn't do this.
In fairness I did get some noticeable benefit from the roof insulation. No doubt it would have been even better had i done it properly.
I'm wondering now if any owner since I sold that house has noticed the problem😮
Hi Steve, loving the videos. I am learning quite a bit about vapour barriers and insulation.
The only part that confuses me is where to vapour barrier the wall?
I'm making a garden room with a warm roof where the osb for the roof will have a sticky vapour barrier applied on top, followed by insulation and then another later of osb on top as you explain in many of your videos.
I will be tucking in the insulation in between the joists under the osb on top of the wall as you explain. My question is if i use a barrier on the inside of the wall and take this over the insulation between the joists (where it's been 'tucked'), what would i do about the joist? if i tape around the joints could there still be a dew point inside the joists themselves due to thermal bridging? will air movement pass through the joists (the wood itself) and pass laterally through the osb? is this even an issue I should be concerned about?
The vapour probability of walls is seen to be different than it is to a roof. Generally speaking, you have a lower vapour control system on a wall or in a lot of applications specially on extensions and old buildings there is no vapour control layer on the wall.
This is so helpful! Thank you so much! However, I really need your advice.
I am preparing to convert the cold flat roof of my dormer to a warm roof. I am having a hard time finding details on a warm roof intersection with a pitched roof.
Could you please share any advice you have around what happens around this intersecting junction.
For instance, should the PIR be mitred to butt up against the pitched rafters or left hollow? And how should the rubber be tucked around the side of the flat roof at this junction.
I would be eternally grateful if you could shed some light on this or even point me to some resources.
Thank you!
All you have to do is make sure that the thermal element is continuous and as thick as all the other elements of insulation as you can sometimes you can't get it as thick but 25 mil is the minimum thickness that you wanna go to
When you've got a house that can't breath, do you leave the windows open to let the moisture out ? I have lot's of drafts in my old house, and it's nice and dry.
steve, how about a air flow through the timber part of the roof. ps; I see a lot of cavities are not covered with Fibre cement sheets to stop moisture going up in the roof space.
They are warm deck roofs, you don't want air flow with warm deck.
It's a warm roof you don't need ventilation on a wall roof. Rob Norman below is correct.
0:20 Don't you extend the insulation on the roof out and over the insulation in the cavity wall?
Okay I'm not quite sure of your question here but you've got thermal insulation on the roof when you get over the top of the wall you turn 90° and drop down if you've got this say 150 mil insulation on the roof that gives you a good quality turn go down try and keep 150 mil therefore you've got no way of having any kind of thermal bridging of course it's very hard to do but that's what you're trying to do. You then drop that 150 down to the top of the wall and stop because there's a wall there the wall isn't thermally that efficient probably however you've done the best you can. Should it be over the top of the cavity or on the internal wall? Well, it wants to be on the internal wall and extend outwards as far as you can so theoretically if you've got loads of insulation left over why not make it 200 mil wide why not go over the top of the cavity? The cavity should be closed at the top anyhow because you don't want warm moist coming up through the cavity into any cavities above where's Timber causing a problem? So do you need to do it irrelevant the main point to take away here is continuous insulation at the same thickness if you can achieve it and also air tightness.
Hi Steve, could you give me a bit of advice. I am building a garden room and the roof joist are 120 x 45(5x2). I was thinking of using(cold roof inside to out ) 12mm plasterboard - 1000guage polythene - 25mm PIR up to joist - 100mm XPS insulation between joists and 20mm air gap under decking with continuous soffit vents back and front. will I get problems only having 20mm air gap
1000 gauge polythene doesn't mean anything. It just means that it's a thick piece of plastic. You need to be using a proper a VLC not just polythene generally an air vapour control layer is coloured green as regards to the rest. It looks amazing if you're building a cold roof 20 mil is on the shallow side because obviously building control say 50 mil but you can take it up a little bit but 20 is a bit shallow personally I wouldn't do a cold roof. Try looking at some of the other roofing systems try looking at using super quilt.
Hi Steve
Hope you can give me a little advice here!
I am doing a warm flat roof using posijoist. I assume I can tuck in between the webbing and foam all the in-between areas?
I also intend to extend the roof to firm a canopy of approx 1m. My architect has suggested we just extend the posijoists however will this not cause cold bridging?
Any ideas on how I could form the canopy instead?
Thanks in advance?
You're quite welcome to send me photos and videos and I will have a look for you but too much detailed to go into here
What stops the rafters from cold bridging through the insulation?
they are covered with insulation
Great video Steve as always. Question's for you as a continuation to whats in the video. Would it be bad or good to fill the joists with extra insulation, and would you use an airtight membrane on underside of joist sealing back to the walls?
The golden rule is that you can put insulation between the joists on a warm roof, providing you only put one-third of the quality, the thermal quality of the insulation. No, you do not need a vapour barrier at that stage. No, you do not need to seal it against the walls at that stage, as you have sealed it against the walls higher up with the vapour barrier.
Would there be an issue putting on insulated plaster board under the joists if I “tuck in the roof”?
The answer is no what you Gotta think of is continuity of the thermal element on a piece of paper do a thick line across the ceiling. Where is the next thermal element? Do all the thermal elements join up to the walls up to the thermal element in the roof is there a break if there's a break? That's where your problem is
Air tightness and thermal bridge removal are critical for optimal energy efficiency, but you should not be doing this without mechanical ventilation to manage indoor humidity and air quality. For good airtightness, a continuous airtightness membrane is needed. You will have leakage between the joists and the wall in your example. Furthermore, exposed joist surfaces are thermal bridges. Insulate your joists as well.
Airtightness and thermal bridging are undoubtedly the most critical considerations here. In the example above, we have two layers fully bonded together, forming a continuous quilt of SuperFOIL. You really cannot achieve a more efficient, airtight, and unbroken quilt than what we’re installing here, close to 40 m² of unbroken thermal quilt.
As with most projects, any potential breakdown will typically occur at the adjoining apartments. In this case, not only does the SuperFOIL wrap around the insulation at the ends of the joists, but we have also filled between the joists-traditionally a weak point. However, as you pointed out, the joists themselves are made of timber, which is actually a relatively good insulator. With the thermal insulation depth at around 150 mm, the exposed area of the joist is minimal, resulting in very little thermal bridging.
Significant effort was put into ensuring airtightness was achieved at every stage. In fact, airtightness was accomplished with the first layer, and the second layer was installed assuming that the first might not be perfectly airtight. There is simply no way this could have been installed to be more airtight than it is now. Apart from the ends of the joists, everything is encapsulated with the same high-performing thermal material throughout.
The builder who was doing our infill extension mixed warm roof with the older style ventilated system, and I had to point out to him that cold air would come directly into his roof and sit in top of the plasterboard ceiling. He didn't understand but I got him to put insulation between the old and the new. Unfortunately, as I am not a builder I didn't see he hadn't done the outer parts that you have pointed out. When I get my flat roof redone, I've a good mind to get the warm roof converted to the match the rest of the flat roof and fix the problems his roof has introduced. The other issue is the existing original flat roof slopes, and the warm roof is flat and sits proud of the old roof. It has leaked and causes the rain water to be directed to one side of the sloped part and now overwhelms the gutters. I fixed the leak as he was blaming the old roof and didn't accept responsibility for his poor work, so I wanted nothing more to do with him, but I wish I had known what you have pointed out. Oh well, lesson learned and thanks for posting.
okay, next time get in touch and we will talk things through
Hi Steve, can I ask how you would ventilate the roof timbers if you fully ‘tuck’ in from the eaves . Cheers 👍
No need for ventilation on a warm roof
@@pauldavies7251a warm roof?? What are you blabbering on about! A roof and attic are hot in summer cold in winter. If you seal a home up with no air flow, it causes moister to condense and cause black mold. And in worse case if you use natural gas cooking you could end up with high levels of carbon monoxide build up! You insulate the FLOOR of the attic, and allow the roof to “breath” and release moisture from the building walls.
@@martinbuss6818it’s a warm roof. The space between the joists is effectively inside the room. Moisture won’t condense inside. There is a vapour barrier above, then 120mm of celotex. You don’t need ventilation in a warm roof.
@@martinbuss6818 I love the arrogance from clueless people 🤦♂️🤐
, A warm roof means the insulation goes outside the main roof so there's absolutely no need for ventilation,
You only need ventilation when you've insulated between joists or rafters,
Aka "cold roof"
@@gdfggggg there's no telling some people is there
Sealed = condensation central.
No.1 reason for my damp surveys over the past 4 years.
In this video, I am forming a wall roof. Warm roofs do not need to be ventilated. cold roofs need ventilating. This video is only about warm roofs that do not need ventilating. In the video, I show that I go around the edges and insulate and make it completely airtight. The insulation around the edges meets the insulation on the roof. Theoretically, you could sit in the room without a ceiling and still be warm.
@@SteveRoofer
It’s not just about the roof space. It’s the whole house.
Houses get used by people. Damp from breath, use of water, drying clothes, etc..
That moisture has to go somewhere & usually ends up around windows & cold walls.
Sealed buildings require active ventilation to remove the moisture from the air, preferably in combination with a heat exchanger.
I’ve had plenty of cases where condensation is a problem for cold roof spaces too, but warm roofs have become a regular occurrence in the last 4 years with both new build & reroofed extensions.
In a ventilated cold roof, there is a wicking action for some moisture to escape through the ceiling &, although when done incorrectly, adds to the condensation issues, a properly installed cold roof or a warm roof with active ventilation will significantly reduce the possibility of condensation issues for your clients.
After reading many of the comments on this video, it seems many folks do not understand that of the two approaches to roof insulation, you are speaking only to how to properly create a "warm roof" as opposed to a "cold roof". Everyone wants a properly insulated ceiling inside yet their are two distinct ways to achieve such. If a homeowner or contractor creates some abomination sharing the worst features of both methods...havoc can and likely will ensue. Thanks for the video.
thanks for the reply
Wouldn't tucking in increase the risk of damp/mould issues due to the lack of airflow?
no because there is no airflow it's a completely sealed unit just like your house you don't have to have airflow around your kitchen table. All the timbers you see in this video the joists are all internal.
Hi Steve, I'm just in the process of replacing my old cold flat roof extension, it runs to the centre with a central gutter. Im fitting a wall plate and having it slope all away from the hoise with new joists above the old.
A few questions, can the existing felted but non insulated roof be left in situ or can this cause problems with damp.
Im intending to put 150mm PIR between the new 200mm joists, leaving a 50mm air gap, followed by a quilted foil over the top of the joists, 50mm battons then 18mm 0SB3 followed by EPDM.
Will this cause any problems, im planning to let air flow across the width of the roof via the gap in the battons above the foil layer.
The existing roof had no insulation in the original 225mm cavity and is finished with polystyrene backed plasterboard.
I understand i will need to expose the ends of the old roof to continue the new roof insulation to the existing brickwork.
Thanks in advance Jonathan
You need to send me an email and ill send you back info
Thanks Steve. These are really useful things to look out for as I look into home projects.
Thanks
How does the roof breathe and not cause condensation if it's been thermally sealed?
Thermal insulation is considered outside of the construction of the building and there is no thermal bridging therefore there wouldn't be no need for ventilation.
Moved into our bungalow with rafter level insulation that was freezing - a massively shoddy job - dropped all the insulation to ceiling level and doubled the thickness - worked this out inadvertently 😮
Did you provide ventilation?
@@ooooobpbpbpooooo the soffits were already ventilating the ceiling so now the air goes up and out through the roof vents instead - one part of the house was already done like this so it’s not clear why they chose to go warm roof on the main part without doing it properly 🤷♂️
Get ready for the 'builders' and 'roofers' who say you need to keep these areas open for air flow. Those guys are absolutely clueless. Have no idea about warm and cold roof sysyems.
Neither have you pal
@@tomthumb1769 and we found one of them. I pity any poor people's homes you've been near.
@@benrichards1 I’m time served bricklayer of 34 years pal what’s your qualifications? Apart from being a know all
@tomthumb1769 Great. Stick to laying bricks, then. Let roofers roof.
@@benrichards1 in your first comment you mentioned roofers with builders so I’m not sure you have any idea what your talking about
@SteveRoofer You mention in the video at 6:25 that this construction does not have a lower deck. I heard the lower deck with OSB is a liability in warm roofs. OSB's glue makes it near non breathable and as such prevents moist air from reaching the top of the insulation and condensate there, eventually leading to the OSB rotting. Do you have thoughts and is there up to date best practices documented about this?
This is a warm pitched roof, not a warm flat roof however it performs exactly the same way and an air control layer should always be at the very bottom so to answer your question yes OSB decking is actually a very good air the controller it's actually in the correct place because on top of it you're gonna put an even better air vapour controller. I think most of the point is when you put OSB on the top of a warm roof. We see that rock an awful lot of the time and a lot of people say you shouldn't do it. I had this conversation with one of my contractors and between him and me we have been doing it for the last 15 years with no problems, but that could be because we use a very good air vapour controller so the sandwich of materials is completely sealed and we don't get a problem.
@@SteveRoofer thanks for your reply. I was thinking about using something like Stamisol DW on top of the insulation, breathable out, waterproof but advertised as offering structural benefits (in fact the only reason why I would be tempted by OSB - or if seeking that benefit plywood seems like a better choice?).
I have no OSB specified in my upcoming warm pitched roof at ALL, just VCL/Tissue facing PIR Insulation/Breather/Battens/Counter and Tiles. Do you think a lower OSB deck is absolutely necessary for structural reasons?
What's the depth of the pieces of ENERTHERM between the rafters meeting the soffit side please? Where does the air breather membrane go? is it already on the other outer side of the insulation? Do you place the vapour control layer on after the insulation is put up then follow with the plasterboard? Thank you:)
okay? First of all the super quote used here is also an air vapour controller so when you're looking up from the bottom you've got an air vapour controller already installed in the correct place. We haven't used any PIR insulation on this roof what you're looking at in the video is the underside of the, super quilt between the joists we will be installing 200 mm of Rockwall. This buildup gives us the correct UValue for building control.
Great video! Can this be done retrospectively? i.e. remove fascia board from the outside and seal it up from there without having to re-roof? Thank you.
How would you tackle a dormer bungalow roof?
The roof line comes down to the same level as the interior ceiling.
Pretty much the same way as we are doing above you're either gonna do cold roof construction or warm roof construction and you're gonna look after the ventilation and the thermal point correctly it's all doable. It's all just down to detailing.
Great video. What do you do about ventilation?
Nothing you don't need it its a warm roof
You need some decent airflow running throughout or you will be creating the perfect habitat for dry rot.
no because you don't have your kitchen table or your kitchen units wrong and all the wood that you're looking at is internal just like your kitchen table and that's because you control the internal environment
Where does the warm air escape to? If there is no air flow wouldn’t that affect the joists? Any sweating?
Thanks for the video by the way 👍🏻
Why would you want your warm air to escape? You spent good money heating it up
That is superbly explained! Thank you very much for this channel Steve. Cyril / Artisan Roofing Limited
I really like my builder, so I'm hoping he's done this on my new extension. I'll be checking when the wind picks up.
Hopefully he's done a good job for you
Why would there be a soffit vent on a warm roof. I thought they did not require any air flow. Someone correct me if I'm wrong. Thanks
No a warm roof does not have to have venting; however depending on what you are doing you may want to vent the independent space of the soffit
@@HampsteadBuildersLt thank you for your reply
You're right it shouldn't be a soffit then on a warm roof if you're referring to this roof it's because there's a cold roof fitted over the top of the warm roof
@baldyslapnut. I can guarantee that at some point water or moisture will get into that warm roof at some point. the home owner will have zero idea its happening until the rot is obvious. it's the same scam as spraying your roof with insulation that mortgage companies are demanding it's removed. it's the same scam as cavity insulation. you need to be able to inspect wood for any problems. sealing everything up to save a couple of degrees is really not worth it.
perhaps moisture will get into the roof, but the thing is is that it's fully vented above for it to get out. It's also got the highest quality air vapour control at the bottom so if Var does get into it from below and the only way it would do is because it would go through the air control layer which is supposed to do but as it's a control layer it controls the amount gaining because the amount getting in is controlled to a point that more can get out above you don't get a buildup because you don't get a buildup. You don't get a problem not only there moisture on its own. It's not necessarily a problem. It's only a problem when it hits something cold and condenses i.e. cold bridging as there's no possibility of cold bridging in this roof therefore there's no chance that the moisture can turn into water and cause a problem it's just physics.
I'm concerned abiut the life of the roof tiles when the roof is highly Insulated and the tiles become frequently frozen. Any insight?
This is one of the most intuitive comments really thinking of what happens in the future and you've actually answered the question that most people do not understand lots of people ask me why I'm against the cold roof construction and the simple reason is because of the amount of insulation that we are now using you have taken away the drying ability of the heat loss. This drying ability will definitely make a difference to any product above. Take it away and you could have problems such as the lifespan of anything like tiles, buttons fixings and so on on this particular job we are using plastic slates but they are still on wood with galvanised nails so without the rising heat just how long will this last? Get back to me in about 20 years time, and I'll tell you how it goes!
So let’s say I did this in my loft…..would I get condensation build up in there???
That depends on your loft if the loft is a cold area as long as you keep the ventilator ventilation and move the air up there you won't have a problem.
I’m confused, I thought a warm roof meant insulation would go on TOP of the decking. This looks like insulation is immediately below the decking. Help me out, what am I missing?
A warm roof does mean that. This video is about how you should bring the insulation from the top, down the sides to meet the wall.
Correct, the insulation should sit on top of the decking which has a layer of felt tacked to it and a 3 layer of polyester membrane torched on top of insulation. A thirty year life. Just one point though, it is not possible to acquire a underwritten 20 year warranty for a F/G or rubber roof?
What about ventilation Steve?Should there be Insultion, a gap for venting?
You don't vent warm deck roofs
thanks mate! I thoughtall roofs need to be vented@@RobNorman08
Thanks again Rob, you're correct looking through some of these replies I can see lots of people are confused warm roofs do not need ventilation cold roofs need ventilation
Thanks, rob, I see you are answering a lot of people for me. This video has got quite a lot of his quite quickly. I need the help. I can't answer them all. I can't believe the amount of people that do not understand why roofs don't need ventilation
@@SteveRoofer I'm a Chippie, been in the trade for 30 years, build loads of warm deck pitched and flat roofs, on lofts/extensions. I've learned that many, many people really haven't the faintest idea how, when and why roofs need or don't need ventilation, There is a huge amount of information available on the subject if only people would take the time to research it rather than blindly harping on about ventilation!..all the best.
We built an extension and put insulation between the joists but it wasn't on the drawing, the architect didn't think of it, so it's not necessarily the tradesmans fault
Oh a lot of time it's not the tradesmen I get lots of professional drawings through that are wrong
What about lack of airflow and damp? Please help.
In this video, I am forming a wall roof. Warm roofs do not need to be ventilated. cold roofs need ventilating. This video is only about warm roofs that do not need ventilating. In the video, I show that I go around the edges and insulate and make it completely airtight. The insulation around the edges meets the insulation on the roof. Theoretically, you could sit in the room without a ceiling and still be warm.
always done this takes time but its well worth it.
Good to hear. I bet you've seen it done incorrectly a few times though?
I thought there was supposed to be no insulation between roof beams as it traps moisture.Which is right?.
I believe depends where the dew point is. If the insulation is airtight and thick enough no moisture reaches the outer wall or condenses in the middle of the insulation.
In this video, I am forming a wall roof. Warm roofs do not need to be ventilated. cold roofs need ventilating. This video is only about warm roofs that do not need ventilating. In the video, I show that I go around the edges and insulate and make it completely airtight. The insulation around the edges meets the insulation on the roof. Theoretically, you could sit in the room without a ceiling and still be warm.
Nice neat block work! Your lucky if you find any of them filled in by any trade. Only time that would happen without getting you guys in,is on the tradesman doing his own work!
Correct DIY,s always do a better job
Hi Steve, very informative, thanks for posting.
I want to replace the polycarb roof on my 3m sq lean to conservatory.
Would you recommend a warm or cold roof? Just worried about the weight of a warm roof. Also what thickness joists would you use on a small roof like mine? Cheers.
I never recommend a cold roof. It just doesn't work.
I'm having an extension built at the moment and they haven't insulated behind the fascias. The problem is there is now a very small gap between the joist and the parallel wall and very little space to get anything in - the only thing I can think of is expanding foam. Any advice?
But what about damp issues , surely you are sealing in damp to roof?
there's no damp in the roof so you won't see anything
Brilliant to see this and at just the right time. We have some real challenges with how our roof has been left on our build. We had a warm flat roof joining a cold roof and one was open to the other. We have closed the junctions tightly with PIR and then painted all of the joints and gaps with passive purple. Even without the build finished we could tell a massive difference. We have a bigger challenge on the eaves of a cold vaulted celiling where the roof PIR was simply no where near joining up with the wall insulation. Would really like your opinion on how to tackle it.
Send over information, videos and photos
@@SteveRoofer Thanks so much for your amazing support. We have found your channel so so useful and your responses to our questions so quickly were such a help. Your points about trades not wanting to spend time doing the right thing are so crucial. Sadly I don't think many general builders are even aware of what they should be doing. The quality of our build in this respect was very poor.
Hi, is expanding foam vapour impermeable (that is can it act as a vapour barrier)?
Good question and the answer is yes it is to quite a high point so realistically when assessing where you're using it you can assess whether or not you need to add further vapour control controls generally speaking. You don't need to add a high vapour control on a vertical wall, although you do need to have some kind of vapour control and the PIR insulation and foam is efficient
5:40 I think lots more water vapour will get into the PIR through the cut end than through the bigger silver sides and make it damp and useless ...
Its like when you have a lot of broken windows mending one doesnt make any difference but when you mend the last one suddenly the house is warmer and less window (actually the one before last cuts the winds)
I'm planning on wrapping my kingspan seconds in membrane like a xmas present and taping it up, any great reason not use any old vapour barrier and tape from Wickes or Toolsation compared with the most expensive sticky packed stuff?
Celotex & wingspan insulat6are closed cell so any moisture which will be minimal won't affect the boards,
but they get damp through the cut ends if left in the rain and take weeks to dry out .... and vapour is smuch smaller than rain molecules @@pauldavies7251
thanks for the video... never knew about the vapour barrier :( (cheers again)
No worries!
Is this essential if the warm roof sits below parapet walls?
I don't quite understand the question. Please ask again.
whats the silver stuff above the joists? I would have expected to see OSB form below in a warm roof? That looks like a vapour control layer?
Its the bottom of supper quilt as this is a warm-pitched roof
Ventilation, condensation ? Eaves vents, ventilation tiles, vented dry ridge ?
Yet sometimes you need to think outside the box.
Hi Steve I'd love you to look at my loft space, condensation everywhere. Discoloured insulation. I think our soffits are being covered up with insulation. House builders have washed their hands of it, marley risk have rejected our claim. Scandalous behaviour!
Thats because moisture condenses on the cold sheathing & gets trapped by the insulation with no way to dry out. To address it, an air permeable insulation (no foil) and dehumidification is needed. The dehumidifier will reduce the amount of moisture that condenses, and a permeable insulation will allow condensate to evaporate (ie when the roof become warm when the sun hits it. The foil membrane traps moisture in. Rockwool (Roxul) is a moisture permeable insulation.
Another option is to use a permeable roofing membrane that allows trapped moisture to escape from the topside of the roof, but you need a roofing configuration has an air gap so for the permeable membrane to work: ie metal, slate, tile roof with lathing set up to draw in air from the soffit up through the ridge cap.
Building science {dot} com has a collection of articles about condensation issues in well insulated homes. They did a lot of experiments to test what did & did not work. You can read them for free.
Send some photos over Steveroofer@gmail.com
Hello. I have a 70’s house, typical brick construction with cavity walls. Where the joists meet the wall there are inch gaps into the cavity. Should these be filled? Also on one side of the house I have an attached (unheated) garage. The joists for the garage flat roof go into the outside leaf of the house cavity wall, again with a gap. Also fill? I feel it’s highly likely that cold air from the garage (and loft) goes into the (filled with fluff) cavity and would make its way into the house.
You have to be careful insulated older homes, as it can lead to rot. What happens in a lot of older homes that have insulation upgrades, is that moisture gets trapped by the insulation & condenses on the cold sheating & joists. Over time they start to rot. Because the older homes aren't insulated & have a lot of air movement, any moisture that does condense quickly evaporates.
What you probably need to do is first get keep your indoor humidity low with a whole house dehumidfier, upgrade your bathroom fans (make sure they work) to pull out bathroom moisture. ideally a Timer on the fan switch is ideal because you can set it and not have to manually turn it off (reason why most people don't use them). And then test a second of your home to see if moisture accumulates. (ie test a section of your home) You need to use a removable insulation such as rockwool. I don't recommend spray foam since you cannot inspect behind it to see if there is a condensation problem.
Thanks, yes I've started with rockwool in the inch gap and then foil tape over the hole on the garage side so far. In the garage it's easily accessible, on the house side it's not because obviously it's in the ceiling space. I think the garage side is lowest risk because the other side of the house (identical except no garage) has no gaps as it's an outside wall. I have zero signs of damp as of now, but will be something I keep a close eye on. I think it is as modern/good as is possible for 1970, pretty square and overengineered.
I have over fascia ventilation in my loft in preparation for doing as much insulation as possible up there. @@guytech7310
Tucking in, as you put it, would that not cause an issue with warm air being trapped inside? Are you not meant to have ventilation from one side to the other?
Not being arsey, genuinely not sure lol
No, this is a warm roof construction you do not have any ventilation so you don't need to move it from one side to the other side.
What’s the best way to rectify this cost effectively? Do you have to remove the ceiling from the inside? Can you do it from the outside by removing the fascia board?
You can do it in many ways. Obviously, you choose the cheapest way if that means taking ceilings down inside or taking gutters and facias off outside or cutting down from up above Whatever way you need to do it.
Hi Steve,
I see below that you have spoke about warm roof and cold roof but my question is, BC (sorry for swearing) have said I MUST have ventilation installed throughout the roof to allow for airflow from the outside through the roof. I have a 150mm joist and I have to use 100mm insulation. Would I be right in thinking I could install the insulation 30mm of the roof lining and this will leave a 20mm gap from the insulation to the wall which I could then fill with insulation, allowing me to "wrap the room" whilst also allowing the ventilation above the insulation for the BC approval?
Is it a warm roof or a cold roof that you are forming?
Hi Steve. Building out a flat roof on a garden room at he moment. warm roof. Is there any point in putting timbers in now ime noggins allowing for the insulation or wait till after ?
do it as you go along
You need to be careful about blocking up the air gap as you can then get condensation in the roof cavity.
He was showing examples of warm roofs (not cold roofs), which don't have a ventilated cavity
Impossible to have condensation inside the insulation, there's a major problem if you have,
Cold roof you need to worry about ventilation between insulation & roof deck
This is perfect timing, I've just built a warm roof, tied into my houses pitched cold roof. Now the joist void under the warm roof is open into the pitched roof loft space. On the inside
Should I close this off?
If the pitched roof is vented i.e. a cold roof, then you've got to stop all that cold air getting into the area between the choice of the warm roof. So yes seal it off
Yes seal it off, but don't forget your loft space needs ventilation.
When roof manufacturer's produce specifications for warm roofs they don't include this and it does often get missed. At a minimum you want as much insulation as there is in the wall.
Yes, I like to say as much thermal insulation as the next thermal element.
Hi Steven. How do you ventilate a loft conversion properly when you have a warm deck flat roof box dormer on one side and on the other you have vaulted rafters which are insulated in between then insulated over them underneath? Cheers
Ridge vents or high level tile vents sufficient to provide at least the equivalent of a continuous 10mm gap....so for a 6m long ridge you would need vents with a total clear vent area of 60,000mm2. You will also need a means of making sure every rafter void is vented by whatever vents you install (so continuous ridge vents, vent tile every rafter or create a vent path at the apex of the roof by providing a flat insulated ceiling just below the ridge, and using the small void above to link the rafters)
With difficulty.
Useful videos. I have a question for a small shed/office I'm rebuilding with a cold roof. Have plenty of space between roof joists for insulation, and space above for ventilation. However, due to being on boundary line there's only a sizeable overhang on the front of the building. Obviously easy to add vents to the soffit at the front - what to do at the rear to help air circulate? Is it possible to get vertical venting that could be fitted at different points along the facia board? Have seen mushroom vents which could enable air to escape upwards, but would prefer to vent straight out the back with less possibility for leaks if possible. Any suggestions or advice welcome.
If it's only a part time she'd office it's not as important to fully vent it as there won't be much condensation build up compared to a kitchen or bathroom where there's heavy use with multiple people & cooking & steam from shower
Where is the air gap between insulation and roof?
The air cap between the insulation and the roof is outside. What you're looking at is internal.
Hello Steve,
Any tips for Insulating around Roof lanterns? seems the joists and upstands they sit on are a thermal bridging issue?
This is always a problem in a cold roof but it's not a problem in a warm roof. One of the reasons we don't do cold risk is because of this problem and the problem of thermal bridging
Wonderful videos (all of them!). I am commenting here hoping it gets the numbers up.
Wow, thank you! The response to this video has been quite amazing. I didn't actually want to post it. I had it in my bin for quite some time thinking that I would never publish it. However, a customer asked me a question, and I sent it to him as a private video; he thought it was amazing and suggested that I put it up, so I did, and it's probably going to be one of my top performing videos. Thanks for your vote
Please understand that this is a warm roof and do your research before attempting this.
If this was a standard cold roof, doing this insulation like that would be wrong.
Good point I didn't think I needed to make that clear when making the video. However, you are correct I should've done
for a SIPS panel garden room, would you say that you need to vent the top like a codl roof, or can you just put DMP on the top of the sips?
well you shouldn't be putting a DMP on top of the roof. You should be putting a roof membrane on top of the roof if you put the zips panels on correctly i.e. no gaps cause that's the big problem with sips and no thermal bridging. Between the panels as they joined together and also an air vapour control layer at the bottom then it's a warmer and you don't need to invent it.
@SteveRoofer sorry, I did actually mean EDPM (diy getting terminology wrong). Panels didn't go amazingly well together, but I foamed and taped any gaps between osb with buytle tapw, and put up vapoour barrier the way you explain with tape etc on underside
Thanks for explaining this Steve. Isn’t cold-bridging of the rafters an issue?
The rafters are all internal buried deep below the insulation. How could you ever get any cold bridging please explain?
@@SteveRoofer Hi Steve, wouldn't there be cold bridging from where the rafters overhang the wall plate to the outside? i.e. the part that the fascia board would normally be nailed onto?
What about rotting caused by cold beanend temperatures? Is that covered?
The cold ends of the joists are fully ventilated by the outside air and will be at outside air temperature or very slightly warmer so no condensation can take place.