Vapour Control Layer on a flat roof. Stop interstitial condensation
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- เผยแพร่เมื่อ 2 ต.ค. 2024
- Time and time again I see the wrong vaper control layer being used and installed incorrectly. Interstitial Condensation can happen if warm air from inside the building gets up and into the roof structure. Interstitial condensation only occurs if all conditions are correct but when it douse the problems can be immense. Interstitial condensation not only happens in the flat roof but can happen anywhere on a building where all the conditions are correct. The issues I see are mainly because of the lack of attention to details, bad workmanship and bad specification of materials.
Interstitial condensation is known outside the trad under several different terms such as "sweating in a roof" "Condensation in a roof." Is now becoming a very big problem
I think a lot of it starts with trapped moisture during construction . wet timbers wet insulation both PIR and rock wool type . wet block work once sealed it cant evaporate . moisture /vapour travels upwards can't escape heats up condense then travels back down into insulation then evaporates again all the time attracting vapour which increasing the problems . it will condensate on a cold surface outer edges block work or under side of ply and so the cycle continues . it takes a lot of heat to evaporate moisture fully and if its trapped its going nowhere
Very informative! You obviously know your stuff with flat roofs
Hi Steve, I have been watching and recommending your videos for a while now and have just came across this one which I had missed but I enjoyed the Blue Peter style video and the presentation. Very useful and informative, thankyou. As a building designer myself its refreshing to see your professional approach to detailing.
Hello Steve, cheers for the video. How do you deal with the expansion of the sub base and the VCL stuck onto it and the walls? Thanks again! Alex
A 2mm gap (3/16") around a 5m (16ft) x 5m roof is the same as a 200mm (8") square hole, so there's plenty of airflow if it's not sealed right. You (I/we) want the moist air to stay warm (non-condensing), and the temperature drop (where the dew point will be located) to be inside the sealed insulation space.
It's all about air tightness and ventilation
Just on with doing a small flat warm roof with EPDM and want thank you for creating your channel it as been great go to channel to helping me to get this small flat roof done its a great resource for diyers pros a like.
Hi Steve, we used Alutrix 600 on the back of this video, what a great product, thank you taking the time to produce such an informative video. We did make an error on the fixings though, we screwed the 150mm PIR to the sub deck with the mushroom fixings.... but then used std pan head screws to fix the top OSB to the ply sub deck.... clearly should have just used the mushroom fixings on top deck....we'll have some cold bridges, but shouldn't be a problem otherwise I hope?
Everyday is a school day - thanks for the video....
Thanks for taking the time to share this info. Very well presented as ever. Keep up the good work. All the best Pete
Thanks
College don’t teach you this quality video thanks buddy
Hi Steve, thank you for all the videos, could you share the link for the silver vapour barrier? Thank you 😊
It's called Alutrix 600.
Really good info there such a valid video im learning so thanks for sharing steve.
Justin brickright 👍🧱🧱🏴
using thermal fixings to secure the top layer of ply will leave a raised edge above the ply. Whatever system your using to waterproof the roof surely seeing them thermal fixings protrude from underneath looks a bit naff. I understand it’s the correct way but wouldn’t a recessed screw and then some wood filler do the same thing or maybe some aluminium foil over the screw head which will then leave a nice smooth finish or would that cause heat loss through the ply ? Also I was always taught that the vapour barrier should form over the insulation board and be sealed back onto the top of it by using tape or sticking the felt depending on what you’ve used for vapour barrier. I just wanna know is that the correct way then or is sticking it to the wall the correct way ?
you can hardly see the raised heads of the thermal fixings it's not a problem at all
Bloody hell Steve this was amazing. What VCL in that silver one?
alutrix 600
To do it correctly not you cant retrofit from underneath I would leave it alone or do it all again correctly. Generally speaking, It will work without the VCL providing other elements are OK like internal moisture is low. No drying clothes and boiling loads of water on the cooker showering or bathing twice a day. Also, the insulation fitted above is tight and gap-free and no thermal bridging to the outside. If all of thease Items are Ok you may not have a problem.
I have watched a few of Steve’s videos, all very well put together by somebody who has a lot of common sense and who has experienced the practical problems you face on site.
Thanks
@@SteveRooferhi Steve, sorry to hijack a different comment. Are you still using a top deck on epdm flat roof? I'm seeing alot of details showing epdm stuck directly to felt faced insulation.
@@leftfootforward1040 Yes 50% of the time
IV seen crowds use as little as 1000guage polythene basically bin bag matieral a 3 mm torch on felt very good option once he fixing come throw they nearly self seal around the felt
Yes see this all the time
Alutrix/resitrix , i love their products as a roofer
Hi , I have just left a comment , also I have to say that they are very good, very practical, thankyou for your efforts. Regards Bob
Fantastic video, really helpful
Glad it was helpful!
Would this be necessary even under a felt roof?
Hi Steve, great video, thanks for taking the time. What is the name of the decent vcl you use and where is best to get it and the thermal breaks for the screws?
Hi Steve, what about a warm roof without vapour barrier with EPDM sheets above a ventilated garage? Do you think it will get a lot of condensation? Does it make sense to put vapour barrier from the inside in the garage ceiling?
Yes definitely needs vapour barrier
Great video Steve, I contacted Visqueen as I was going to use a vapour check (thin plastic) on my warm roof. Their technical person told me to use a bonded vapour check as you demonstrated. I'm glad I checked and also your video was very informative!! A+
Glad I could help send over some photos of the build perhaps I can use them
According to my builder because he is using unilin 1500mm celotex insulation, he doesn’t need a vapour barrier under the insulation on a warm flat roof. Is this true?
Hi - I’m just designing my warm roof solution for an existing flat roof, thanks for your videos they are really informative.
I intend to use Alutrix 600 but wanted to ask about it securing to a concrete slab roof - would you use any primer or additional adhesive
Also what mechanical fittings would you recommend for securing the new insulation and osb to the concrete slab
Thanks in advance
Hi Steve great videos. From a fellow flat roofer.
Pu and Pmma. Installed correctly they are brilliant systems. Svap 2000. Decothane, sikalastics, 618, 625, balcons, flakes, chippings., WeCryl, Thixotropic, rapid. Garland, Bauder, iko, Westwood, But never never GRP.
I think the use of glass fibre is all because some salesperson wanted to move an awful lot of raisins and glass fibre has got a good name it is a good product just look at boats they sit in water year after year and glass fibre amazing however a roof environment brings along completely different problems and glass fibre is just too expensive to be laid in the thicknesses and with the expansion that isn't necessary to make it last
@SteveRoofer A roofer has recently done me a quote for mine and my neighbours dormer flat roof. He wants to use renolit alkorplan f, anyone have any experience of this system? Thanks
Hi Steve, would you be able to let me know who manufactures the VCL you use?
ALUTRIX 600 Self Adhesive Vapour Barrier my suppliers are www.sdtimber.co.uk I also get all my insulation and timber from them very good service
Can’t agree with a lot of what was said, I would always bond the VB, the insulation and the waterproofing. Prevents damaging the VCL and potential cold bridging with fixings.
Steve you are amazing sir! I will build my roof only with your knowledge and professionalism from your TH-cam channel . Thank you so much for your videos. Please don't stop teaching and showing how should be done correctly, it really worth for a lot of people! Cheers
If you haven got a ceiling then the internal humidity is high you will have that problem. Send me some photos and ill have a look
@steve roofer - May I ask what that brand of that super sticky barrier that you use is? Thanks
alutrix 600
@@HampsteadBuildersLt thanks
Can you give the name of the vapour barrier and who stocks this product thanks
Using visqeen on a flat roof is asking for trouble unless it's thrown over it completely as a emergency to keep the rain out
Hi, I live above a garage in a semi which floods ( on the thames ), there is no the ceiling on the garge at present, it is completely open you can see the floor from underneath. I am looking to put a ceiling up how do I fit a vapour barrier and insulation and what type of plaster board or do I use water proof ply. Regards Bob
Thanks Steve, could you cut the vcl into the brickwork and point, the same as lead flashing?
Hi Steve, nice vidoes, many thanks. I am working on a cold flat roof for my garden room, I have well ventilated roof, vented soffits at each end. I am getting to the installation of the vapuor barrier internally, as I have installed the PIR. I was looking at using foil tape over the joists, sealing att the foil bacvked PIR together creating a vapour barrier. What Vapour barrier would you suggest please?
there are many suppliers try Visqueen Novia, or Siga Make sure you pick one that is in category two or above
Tape all joints make air tight
@@SteveRoofer Thanks Steve, a couple more questions....
1. Is this suitable, www.roofingsuperstore.co.uk/product/polythene-vapour-control-layer-500-gauge-27m-x-50m-roll.html ?
2. How do you make plug sockets air tight ?
@@speedyrazor1 the spec indicates that it could be but is pretty vague. If it was me I would go for the 120 www.roofingsuperstore.co.uk/product/polythene-vapour-control-layer-1200-gauge-4m-x-25m-roll.html the minimum specification on this one is over the required minim for vaper resistance in a domestic building. Don't forget to get all the tapes you need also. "How do you make plug sockets airtight ?" with difficulty. Use a butyl sealer tape
@@SteveRoofer Thanks Steve, is there any video or explanation on sealing plug sockets please?
I paid a roofer to install a torch down roof on our flat roof, he didint add any insulation at all...now I have a condensation problem on the inside of building. Water dripping off beams when the building begins to heat up. Should I insulate from underneath, I'm afraid to install drywall because of condensation dripping on it in the 12 inch space between the drywall and the roof covering...any suggestions?
I know that your comment is now seven months old but unless you discussed having insulation added to the roof structure with your roofer therefore allowing him to price it in to the job then of course he isn't going to install any. A competent and conscientious roofer would have brought up the possible need for insulation with you when pricing the job,you should also bear in mind that until the old roof is stripped then he isn't going to know if there is any insulation.in there or not.
Tip : speed up the video 1.5 times or more . Otherwise, a lot of faffing about .
Nevertheless , thanks for the upload .
Hi Steve great video .. my roofer tells me he wants OSB up and over the wall? Am I ok to seal my Vapour barrier to the OSB or is this defeating the object and still letting vapour between the OSB and the wall? thanks Gaz
I don't like putting OSB up and over roofs it can run with moisture getting through the wall. If you do do it try and put a damp proof membrane between it and the wall.
Yes you seal the vapour control layer to the OSB
How would I put spotlights in (kingspan 100mm and vapour barrier in Flat cold roof) without creating an opening on the vapour membrane
Better to use a track system - don’t break the vapour barrier , if you must run down lighters then counter baton and make a void below the insulation and VP , better for wires too
if the mechanical fixing is piecing the vapor barrier at the bottom, doesn't that compromise the whole structure?
No, first of all the vapour control layer, sills self around the fixings so there is very little leakage of around then however it's such a small amount of holes. If everything else is at a time it's not a problem the construction is extremely forgiving and I emphasise the word, extremely unlike a cold with construction that is already working on its limits so needs to be installed very very well to make sure it works.
Hi Steve we have an old ground floor flat roof extension on our house.it is a cold roof in which I want to put kingspan 25 mm inside attached to the existing plasterboard ceiling and then put another plasterboard layer. I say this as the extension ceiling is actually 2 inches higher than the actual house. What's your opinion on upgrading a cold roof on this type of build? Regards Paul.
lots of other factors to take into account send me drawings
Can someone tell me why people don't tape over the screw head?
Both he's using there are both suitable. The moisture build up in a warm roof is minimal. Tiny tiny droplets if any. Never full saturation or ponding within the roof build up. If you have that there's a clear problem either not enough insulation or you have a leak. I use sarna vap or similar on all single ply roofs or occasionally 2mm sanded torch on vcl if boards are adhered. Alutrix the silver one he's using is for hi spec jobs like on a warm roof with zinc or copper where it has to fully sealed. You can't adhere boards to a alutrix vcl they say you can but it's more for mech fix as the pu doesn't adhere well to the sheen flat surface.
Hi Steve , could i ask what type of vapor barrier to use for warm flat roof and where to buy ? thanks
What if you sealed the edges with Flash band tape , priming the areas in contact, then apply your polythene vapour barrier of choice?
Yes you could but you need to use good robust materials to last years not DIY products
What you are talking about doing is a warm roof with a vented space over the top I agree its the way to go however it has cost and hight restraints but ultimately the best
Good quetion. I dont know will have to look into it. If you find out first please point me to the correct info
Really great advice from an honest guy
Excellent, thanks.. Would it not make sense to roll out and staple/tape wide rolls of vapour barrier, or even better, thick DPM directly over the roof joists and then the 18mm osb or ply over that, stopping the moisture at the earliest point? I'm doing my garage roof in a couple of days so would greatly appreciate the response. Thanks.
No, this would just tend to trap moisture in the roof and rot the osb.
What do you use for a primer to put on the bricks? Thanks
I believe the installation guide for the ALUTRIX 600 Self Adhesive Vapour Barrier will contain this info.
Are you screwing into just the sub deck or the rafters as well?
Thank you for sharing your thoughts so thoroughly!
Thanks for the vid! My builder did not install a VCL in the warm flat roof. We have; joists/decking/100mm celotex/decking/roof sealing. Is it possible to fix this by adding a VCL to the ceiling (under the joists) or will that cause other issues? Should they redo the whole roof? Thanks for your advice, Jeroen
Hi Steve, Can you tell me please what primer you use for the walls where the sticky vapour barrier adheres too
we use a contact adhesive however as long as the walls are not dusty it will stick to them so try just unbonding them
Great video Steve. Assuming the final rubber surface can't let vapour out, any water that was inherent in the materials becomes trapped. That being the case, is that ok? As you suggest you see this insulation sat outside in all weathers with assumed pints of water absorbed. As such is there a case for a one way valve or the like? Once the compartment has been heated it expels excess air and vapour etc.
Most of the roof coverings we use do let vaper out so anything that gets past the VCL should get out. Now Trada are saying that no wood products shoud be used above the VCL so we are now laying the rubber EPDM directly to the insulation
If you look at all the singly ply & 2 layer bitumen membrane manufacturers details for a warm roof build ups such as sika & bauder they show waterproof membrane laid directly onto insulation. Putting ply on top of the insulation is like putting a cold roof on top of a warm roof with no ventilation gap. The main issue on a warm roof is you have to be careful of is wind uplift of the insulation & waterproofing if not correctly fixed down or ballasted . Appreciate the info on the correct way to install the right spec vapour control layer👍
You are correct that the EPDM is waterproof and completely blocks the passage of water vapour, so any vapour that gets into the roof is trapped there. This is why TRADA now say that there should be no timber above a vapour barrier. The only materials you can put into that sealed space are one that won’t mind the high humidity, i.e. man-made insulation. Anything else is going to rot. I don’t think it helps that Steve didn’t differentiate between a vapour barrier (completely impermeable) and a vapour control layer. A true vcl slows down vapour transfer but doesn’t stop it. You don’t want a vcl on top of the deck of a warm flat roof, you need a complete vapour barrier. This keeps the moisture in the decking (which is warm) - where it can dry from underneath - assuming the interior finish doesn’t include a vcl that is too high a spec so that water vapour can’t move through it if it needs to.
Dude stay focused, you are going over to many steps.
Hi Steve, what type of the vapour barrier is that sticking silver. What brand of vapour barrier it is. Thank you for great video and good advise. 👏👏👏👍
Alutrix 600
@@SteveRoofer Thank you 👍
What if you didn't put in a vapour barrier and just used a 2 inch air gap?
Hi Steve
Great video, what is the vcl you are using and where can I buy it?
Is that s-vap the sika product? It’s the best but pricey
No that's Alutrix600 and its still very pricy
is primer very important for alutrix vapor barrier ?
Thanks for your excellent videos Steve. I’ve built a vented flat roof. I’m putting 25mm polystyrene insulation between 4x2 rafters leaving a good air gap between insulation and OSB. Then I’ll put vapour barrier and 9mm ply sheet. Will that be enough to stop condensation on underside of felt roof? Appreciate your help with that...
I cant comment as don't understand send me a drawing by email steveroofer@gmail.com
All of that is bs . Put down a vapor barrier and move on. In 30 plus years of commercial roofing. I've never heard such crap. It's not that difficult. Unless you've roofing a rain forest. It's not that big of a issue.
I genuinely hate pir it’s problematic and the sheer amount of waste is ridiculous along with the fact it ends up on landfill.
So so I. I like new multifoil insulations
Ply in UK used to be 3 grades: 1 Interior. 2 WPB (water and boil proof) excellent exterior grade for roofing etc, and 3 Marine, like WPB on steroids and never really needed by builders. Now timber merchants stare at you blank if you ask for WBP or simply lie and say it is - even though it has no stamp to confirm. "Marine" ply today is nowhere near as good as interior grade ply of old because the adhesive used in all OSB/ply in UK today seems about as good as children's flour and water play glue. I have not seen a decent exterior/WBP ply/OSB in over 15 years. Oh, and schools are teaching children we're getting smarter as time goes by...
Don't get me onto this you are bang on the money perhaps its an age thing
Is this vapour barrier butyl based, and how does it fair with GFR roof? Surely the use of fiberglass roofing resin will prevent the moisture from penetrating?
You are exactly what I needed. Been trying to solve a flat roof on my first house. Thank you!
Hi steve , can there be condensation in the wood op top of the insulation , due to insulation difference ?
I don't quite understand your question, however yes there could be condensation in the top wood if the insulation and the air vapour control layer are not installed correctly
Hello super vidéo What’s brand of silver vapor barrier? Will it work with concrete slab? Thanks!
Talk about belt and braces, i would like to ask is this only about flat roofs,we recently had an extension,but pitched with tiles, and i don,t think they did a vapor barrier, all the insulation went in there to spec and the building inspector seemed more than happy,.
Hi Steve can you use your vapour barrier on a cold roof if so do you have a video or drawing of how it should b done .if not which vapour barrier should i use and how should it b fixed . Thanks Steve your a star .
Why not foam the first board to The Brick before your vapor barrier just asking
Heya, how about using plasterboard between insulation and EPDM instead of wood to add protection?
this is a great video. i have a very old, single skinned open ( no ceiling ) garage I'm insulating. its far more complected than i thought,having spend the last week googling " how do i insulate my single skinned garage"
how did you get on? I am thinking of doing exactly the same (with the addition of a rear attached flat roof porch)
Good informative video Steve. Hope you do more
Thanks yes lots more coming anything you want me to cover?
Is there any reason you can't put your vapor barrier below your subfloor (the bottom ply directly on the joist) and use the plywood to pin it tight against the wall (assuming it it flush)?
I just started your video and have a flat roof that gets hot and need it to last a long time. So I’ve seen how guys install aluminum foil over the black roofing paper and tar which reflects the sun and keeps the roof a whole lot cooler. Plus the glued down aluminum foil protects the roof. I would think just keeping the roof cooler like that would add years to its life. They only put in 2 inch drain pipe in the the four corners of the the rectangle shaped roof so this big tree always clogs the drains real bad from the pine needles. Haven’t been able to clear them so need to find a way or just go to the hassle of putting in larger diameter drains and pipe so they don’t get clogged. Homeowners association won’t get rid of the trees nor I doubt they want to pay for my roof damage since water pools up bad when it rains and overflows off the edges of the roof. Very frustrating and I just don’t have much extra cash to have someone come fix it plus hard to trust guys these days to do it right.
by the time you glue down he foil you may as well go buy sola effective paint and paint the roof that's the better way of dining it
Great video m8 what's the name of the viper barrier cheers 🍻
Hi Steve thanks thanks for your answer I’m building a flat warm roof in the west of Ireland and want to use a rubber Epdm , so should I use a 4 mm torch on felt and torcher on to sub deck and sides , iam building this between two slated roofs which I have stripper slates off on both sides the flat roof is a new build with 120 mm insulation sandwiched with plywood on the bottom and osb on top , thanks again for your knowledge your are right the different types water proof plywood the most of it is poor quality material The glue seems to fail Thanhs Patrick
You need to find out from the suppliers if 4mm of felt gives the correct vaper risetance. But read between he lines. We are always told that old felt roofs and asphalt roofs make good VCLs
Hi, does the vcl achieve euroclass B rating fire rating when use in walls and Roof?
Hi Steve, I hope you're still around as I've just found your very informative set of videos!
Can you explain those mechanical fixings please: are they simply fixing the top deck of ply to the lower deck (through the insulation) or should they be fixing into the roof joists themselves (in which case it might be easy to miss the joist positions?)
Also, the fixings will penetrate the vapour barrier: are there any issues there?
Thanks
We would all like them to hit the joists, however probably 90% of them down as long as the lower OSB is properly fixed. That's not a problem. As regards the vapour control layer been punctured again that's not a problem as it is such a small hole and a leakage is so minimal.
What type of fasteners do you use to penetrate the the 140mm insulation, vapor barrier, and secure to the osb decking?
I should be on commission from fix fast.com, as that's where we get our fixings and that's where I tell everybody to go
What you have done is moved the dew point using timber on the insulation. Not a good idea condensation will occur beneath the membrane this will rot the timber. all you need to do is use the correct Ins. board other than that good video ,I liked it. Steve G
I sort of agree with you but I think your wording is incorrect. Are you suggesting nit using the decking under the memebrain?
Sorry ....what company
manufacturers the vapour barrier you recommend ie supplier and code and price .....and also is it same principle if I decide to use a fibre glass flat roof finish
Alutrix 600 and yes same principle if you use GRP however unless you are extremely experienced at housing GRP doesn't use it on a roof when I say experienced I mean you understand that you cannot lay outside without controlling the environment or having the correct weather window you understand how and where to put expansion you understand how to mix and build up the different layers. 90% of all roofs I look at that are leaking are up to 5 years old and are GRP laid badly 6 to 10 a week
Hello Steve,
Great video, it has definitely given me the knowledge I needed. I have a question I am hoping you can answer. I need to place a warm roof at the top of an old church tower, quite a small area, only 8 ft x 8 ft. The walls are lime stone pointed between with lime. The walls do get wet every so often, the water can come through the thick walls and make the wall damp inside, but when the rain stops the walls dry out, it's normal for old limestone buildings to do this when you get rain for a sustained period.
Can I ask, will the Alutrix 600 stick to a wall that does get damp/wet every so often, if the answer is no can you think of any alternative that could be used. Many Thanks in advance.
What’s the difference of putting it up the walls and putting it up the walls ?
Thank you. What length are the screws? Do they have to stop in the bottom ply or go through and maybe into the joists?
The length of the screws are long enough so that you can go into the OSB decking below and penetrate into the joist. If you can find them most of the time you can't find them we always try and make sure the screws long enough that it protrude through the OSB, at least another 35,40 mm.
Good video. I know you used 2 pieces of insulation for demonstration purposes but in reality would t be acceptable to be able to stack 2 pieces on top of each other?
yes as long as you offset the panel edges
@@ak420dave7 its actually better to use two and offset vs one layer
hi Steve patrick here from ireland great video , i was just wondering could i use a 2 mm torch on felt heated on as a vapour barrier thank you
You can use felt but it has to be quite thick from memory, 2mm probably won't get you to the correct specification however it will be airtight and as far as I'm concerned that is the one thing you defiantly need to achieve
In this stack, is the ceiling of the room attached to the underside of the battens on top of your workbench? So the plasterboard or whatever is exactly where the surface of your workbench is?
Yes that's where the ceiling will be
The vapour barrier normally goes between the plasterboard ceiling and the underside of the joists.
Yes on a cold roof but not on a warm flat roof
Hi Steve. You think is correct? "200x50mm timbers fixed between beams/bearers at centres by engineer. Fall to be created per roof plan with diminishing battens on top of joists and 15mm marine ply deck over. 120mm Kingspan TR27 LPC/FM insulation laid over deck forming warm roof. Glidevale VP400 breather mambrane to be dressed over insulation and down face of perimeter beams. 15mm marine ply over insulation"
Want know is correct order of the layers? Glidevale on isolation? Thanks
No its all wrong email me with more info and lets see if I can help
This is the problem these days. There's so many overlapping rules, jurisdictions, products, standards and then a load of crappy/careless workmanship that becomes entrenched in the system. Majority have only ever seen things being done incorrectly. or don't care anymore, I wouldn't have a new house given. Rant over.
I see you’re using bricks, are they London bricks and are they more expensive or cheaper than modern bricks used in roofing?
Would waterproof ply be a certain colour? Or it it marked with a code etc?
Excellent video. Very well explained. Learning all the time. Thank you for taking the time and trouble to prepare. 👍
Hi Steve, thanks for the video. What was the product name for the self adhering VCL?
Alutrix 600
How do you screw the blue plastic tab down. Do you drill a hole in the plywood?
Yes about a 12mm hole
Hi. Which vapour barrier do you use please. Thanks
alutrix 600