Vapour barriers for roofs and walls explained
ฝัง
- เผยแพร่เมื่อ 12 ก.พ. 2022
- Vapour barriers for cold roofs is one of the top questions I'm asked by email and on the phone.
What is the correct vapour barrier for a cold flat roof? The answer is the one that's on the specifications for the project you are building. If you are building a domestic building in the UK you need Building Control and possibly planning permission. To get through Building Control you should have some sort of drawings and some specifications (these specifications should have all the details you need to construct the building, however normally they have been cut back to keep costs down). The drawings will help to get you through Building Control but what you really need are construction drawings with specifications containing details on them. A lot of the time the details are missing. This omission makes up a large part of the problem we have in construction today; without the details and specifications you don't know what air Vapour Control Layer (AVCL) or vapour barrier to use. Depending on the buildup of the roof or the wall, the designers should have done dew point calculations, and worked out the resistance needed to stop condensation forming on the inside of the building. This is called interstitial condensation when it forms in a wall or roof structure. There are many vapour barriers on the market, some have very high resistances to moisture and some low, all are vapour control layers and nearly all of them also control the movement of air. This is what we call the Air Vapour Control Layers.
If you use a vapour barrier that's very strong, i.e. it stops a lot of vapour passing through a wall or a ceiling into a roof, then you need to deal with the moisture left in the room with ventilation of some kind. If however, the vapour barrier you use is too weak and moisture gets through into the buildup of the wall or roof, then it may get stuck there and cause problems like rot in the internal timbers or the back of the roof. With a cold roof it's essential to make sure that above the insulation and below the roof there is a good vented void to remove any moisture that makes it up into the construction. The vented void can then allow the wind to blow the moisture out, basically it's a second line of defence.
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Steven Dickinson
London flat roofing
07802300099
info@londonflatroofing.co.uk
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Brilliant set of videos wish i checked this before reading hours of planning docs to try simplify the various flat roof designs and construction
So glad you are making these videos with really useful content. I love watching them - its an education especially as most of us have old stock property that needs some insulation, but even for new and self builds. Thanks for sharing your knowledge.
Glad you like them!
Another great vid ! Steve you absolutely saved my skin on my house project flat roof a good few moths back I was so grateful for your time and effort in helping me with clear video points and all you wanted in return was a thumbs up 👍 .. what a gentleman and a complete professional . Than you .
Thanks glad to help
A very practical video. Great advice and so true about the internet.
Great video Steve. I really apreciate your videos, im not a builder but i think this info is really usefull for the average person as everyone should have an understaning of these things so they can question trades who are working on their poperty. Looking forward to your video on correct fitting of downlighters in vapour barriers. Thanks
Great to hear!
Extremely helpful Steve, thank you.
Wicked Steve. Thanks a lot mate. You’re a
Legend.
Great vid Steve, been waiting for this one since we spoke via email
Cool, thanks
Great video, thank you 👍
Glad you enjoyed it
Love the outside rig Steve. Would be interesting to build a mini 'wrong' roof one day and see the effects of it, incorrectly fitted downlighters and all! I guess the most challenging one is the rear extension with roof lantern and kitchen below, no abutment vent, the usual 20 spotlights. Just trying to give you a few ideas!
If I get the chance I will do some thing wrong in this rig
Been there done it seen it fail , spotlights letting moisture through & also the heat they create causing condensation. I have seen top hat fire rated led covers to help this problem. The building control like great big cut outs around the light fitting is the problem.
Fantastic explanation. thank you so much for this video.
Really helpful again mate. I’m almost ready to fit vapour barrier to cold roof, it’s the downlight scenario I’m trying to get my head round. Looking forward to see your video on that, I had in my head where I cut the insulation away I will vapour barrier that area, like putting vapour barrier inside an empty box if that makes sense, but I guess there has to be a hole for the cable? 🤯
Tomorrow afternoon
Very useful.
Glad you think so!
Great video! Can I say as someone on the design side, that when specific products are named it's often pushed back by a builder as they either have no history with the named product or simply that their favoured merchant doesn't stock it. It's not easy on this side either and usually results in a phone call with an answer needed in about 10 minutes as to "whether 'X' membrane would be alright?".
Great point and since COVID that ten minutes is 40minutes
Hi Steve, I'm so glad I've come across your video. I'm sure you've spoken about this many times. I'm currently doing a DIY renovation to my property we have an old extension, cold flat roof. The roof joists are roughly 5 inches high. So what I've done is kept 5cm gap from the flat roof and drilled holes in the joists for air flow, immediately after the 5cm gap, I've then insulated with 5cm celotex and taped with alluminium tape for air tightness, which leaves me a remaining gap about 2-3cm from the bottom of the joists, this allows me to fit downlights without obstructing the insulation to allowing heat of the lights not having much effect. Can you please advise further, I'd be happy to email :). Many thanks.
Sunday Ill have a video coming out that covers down lighters
Great video, in construction years and membranes can be so confusing. What I've taken from this, is do the proper research if you want to a good job. For vapour barrier membrane AIR TIGHTNESS is key, that's why they give you the tapes with it.
Great vid! Sealing of light fittings would be esp using fore hoods as I'm just about to redo my cold loft.
Thats my next video
@@SteveRoofer Tha's good news, I've followed eco-home-essentials website "How to Install Insulation in Your Attic Correctly" if you have any comments on that they would be good to hear. I'm going to be using Tyvek Airguard Smart for vapour control -- and thanks to you realise I need more butyl tape!
Can you do a video on vapour control on a single brick building with studs inside instead of block. Do these need a vapour barrier or a breathable membrane outside. Garden office, not part of main house.
great video explaining how to do it the right way. If I build a warm roof over a single block shed that has a vapour barrier in the roof, do I just use a vapour barrier on the walls up to the joins or does the whole internal space need to be completely sealed?
Great videos, thank you! I'm DIY renovating a terraced back to back house with only one solid brick external wall. I'd like to insulate this wall internally as I've had all the plaster removed back to brick. The plan is to fix studs to the wall at 600 centres and place 60mm Rockwool for sound and thermal insulation and then regular plasterboard on top. Is it a requirement to add a vapour barrier to this one wall?? Thanks in advance.
hello Steve,I would like to ask how to install kingspan PIR in our attic.Its end terrace 1958-59,cavity wall with concrete tiles and bitumen felt,average humidity in the loft is over 80%RH in Winter and all stored stuff gets moulded,even rafters. We are in the process to reroof,so replace few bad twisted rafters,install tyvek membrane and new tiles.If I want to keep attic for stuff storage,but still having it fairly insulated from ambient temperature,can I use PIR panels between rafters leaving 40-50mm vent channel behind. There is going to be over fascia vent and dry vent ridge installed. Is this good solution? thanks
The plasterboard that now comes with a vapour control layer built in - does that provide the same protection?
I happened to have a ton of dyneema fabric ( cuben fiber). Do you recon, I can use it as a vapor barrier?
Cam I use thick Heavy Duty Black Polythene Sheet as a vapour barier and bitumen flashband as a tape? Just to save money...
Hi Steve I've been having a long think about how to insulate around my led downlights and have decided to use 60mm all over in a 6 inch timbererd flat roof. My idea is to cut the insulation short to allow for clearance for the downlight then sticking a 25mm insulation piece on top of the 60mm creating a kind of top hat sealed void. Then I can vapour barrier the whole area and stick the barrier to the flush to timber 60mm insulation around the downlight void area,any thoughts mate much appreciated 👍
This sundays video is how to fit downlighters
Hi Steve, what about insulating a Van? Metal? Air gab yes/no? Vaper barrier yes/no? What is wise here? I mean it's not the same as a house right? What do you think would be wise when it comes to insulating a van like Ford transit or Fiat ducato Mercedes sprinter etc. On bare metal. Lots of moisture probably. Should it be able to breath? Or not? So many possibilities and questions.
Is a vapour barrier still needed if using Gapotape on the PIR? Thanks.
How would you do a vapour barrier on a brick wall where the kingspan is foam stuck on the brickwork and the plasterboard foam suck onto the kingspan
As a spark I’m interested to see what you think about downlight installations and what you think is a way forward to improve vapour control.
I recorded that vide last week and it will be out this coming sunday
No Skills - Hi mate, I think the majority of fire rated down lights are also Part C compliant (Resistance to contaminants and moisture).
Don't
@@user-ix4ge6rr7u thanks - I’ll have to do some research.
Great Video, i have watched a good few about vapour barriers trust me. I currently have a single skin (concrete block) summer house. Would you say i have it right when insulating the walls to have 1. Breathable membrane, 2. Kingspan insulation in a stud frame and then the vapour barrier before cladding or would it be vapour barrier at step one on the side of the block and insualtion or the warm side of the room or both? Hope that makes sense. Thanks in advance
Any advance steve would be much appreciated
Thanks
Hi Steve. Thanks for this, really helpful. Quick question though... As you say, the butyl tape is expensive. Is there any reason why you couldn't seal joints with polybutene sealant or something similar? Seems like it would be significantly cheaper to do so.
If you're gonna do it, you have to do it using the system so that you can get the guarantees but realistically don't do it and do a warm roof. If you do a warm roof it's far better and you don't have all these problems
I think one of the reasons people don't specify an err....specific product for a vapour barrier is that they don't know which one to use. Another is it's good practice to put vapour barrier on a detail, and then the specification document or side drawing notes would call up the exact thing or requirements of the thing (such as "comply with BS such and such). It is a jungle, I hate the amount of different and varying products and how confusing it all is. Even if you used NBS spec (costs a fortune) there will be many decisions to be made, and it seems to need specialised knowledge now that even architects will struggle with. What happens is firms will end up having a standard wpec they always use, which is great, until they do something different but the spec doesn't change to suit. Minefield is construction now, it can't have always been so complicated and over engineered?
So if the barrier is on the inside what stops the insulation from getting mouldy? Also how do you attach a plaster sheet to a plastic vapour barrier?
Hi Steve I have a question if you could please answer :) …
I’m looking to knock a non-structural wall down to make my downstairs bathroom a little bigger so its connected with the toilet which is at the back of house however the toilet room is a single external brick wall so it’s very cold which im hoping to insulate and make warm..
Taking advice from this video this means I could make a stud frame 4x2 and fit against the wall and then fit 100mm PIR boards up tight against the studs and that should do the trick no vapour barrier needed? For extra reassurance I could buy expanding foam and put around the PIR to stop any worries about the condensation to meet regulations?
Any advice on insulating a single brick wall is welcome, hope u can help me 🙏🏼
Yes you do need a vapour barrier the rest you have got ok
@@SteveRoofer hi Steve what vapour barrier would I need and how do I attach the vapour barrier to the brick? Do I leave an air gap or no?
Hope you can help as not many people know how to on my situation which is making me feel very confused.
Thank you 🙏🏼
Hi Steve, finding your videos very helpful.... I have a warm roof on a single skin brick wall in a conservatory. Just about to insulate the walls. Could you point me towards your video on warm roofs ? Many thanks
th-cam.com/video/WZ6Ng6YI9OA/w-d-xo.html&ab_channel=SteveRoofer
Warm roofs are technically better as you don’t have a cold void to allow condensation to form
Static caravans (flat cold roofs) - would be interested on your take re vapour barriers and excessive condensation. Mine uses the silver thermal /vapour barrier in the cavity between the ceiling and the external tin roof, above a 1.5" layer of rockwall (or similar) and air vents are punchured through poorly and the seal is not remade around them, they are huge condensation traps in this state, leading to dripping on ya head!
that's just thermal bridging for you
@@SteveRoofer I've resealed the foil all around the vents and it appears to have solved the huge condensation and dripping issues, but I wonder how to check now it's all sealed, should have installed roof cam 🤣
Hi steve im doing a warm roof and wanted to ask ive got the aultrix 600 vapour barrier going down on osb board do i need to use primer to stick the vapour barrier down also the top deck of osb boards can i use long screw to go through directly to the joist or do i need to use the plastic fixing seen in your other videos? Thanks
If you are screwing down the insulation, no you don't have to use a primer. I would always use thermally broken fixings when mechanically fixing down the insulation.
@@SteveRoofer thanks for your reply, i was also wonder if i can use a torch on felt underlay which come in 1m x 16mm as a vapour barrier instead of aultrix 60, also have you heard or used elotene dsn self adhesive vapour barrier is it as good as aultrix 600? Thanks
@@asdaasda4967 Their vapour resistance is the same very good and the price is basically the same I have used lots of different one not the elotene DSN self-adhesive vapour barrier I know some of them are more stickier than others, and we found that the aultrix 600 is the most sticky at the back and that's why we like it
One way of getting through this minefield of vapour barriers is to always go for the highest grade on the market. I now specify Intello Plus on all my jobs since it reacts differently to any other membranes: it stops the moisture going through your build-up in winter and it lets any intersticial condensation dry out in summer by opening its pores. In a way, it's an acceptance of not perfect workmanship on site and will resolve some of the moisture building up in your voids. Very clever.
Yes good point I will be testing some of the new intelligent membains shortly
@@SteveRoofer Hi Steve, did you manage to do any tests on the intelligent membranes ?
@@SteveRoofer Any tests on intelligent membrains? I also would like to know more about this. Your insights are much appreciated!
Hi Steve, what about vapour control plasterboard/ foil backed plasterboard? Does this count as s vapour barrier on a retro re fit?
How would you seal the joints? One of these double sided butyle tapes on the studs then the boards screwed up in to it?
Yes foil back PB can't be mad air tight
I'm looking at VCLs online now after watching this & I'm realising your lucky if the retailer even lists the gauge or mu of the membrane, let alone info like SD values etc 🙄
All good for my new building where I have been following all the advice discussed with you in the past, but now I'm building a solar shed for all the electronics where there should not be much vapour other than what was there initially. I was thinking of making this unit an air/moisture-tight one from the outside rather than worrying too much about the inside since I'm also adopting a "Warm roof" as well. Any suggestions from this fraternity ?
Thanks for this. So if I build a garden room and install a vapour barrier CORRECTLY, where does all the moisture go now that the building is air tight?
If it’s a heated room, the moisture stays suspended in the air.
If its un-heated, there’s no temperature difference (inside to outside ie cold spots) on any surface for the water to settle out.
Good question! you need to vent internally and manage the internal air space, how you do this depends on the usage of the dwelling a Mechanical Ventilation Heat Recovery (MVHR) system may be necessary. You cant have things both ways. Live in a highly insulated airtight space and not expect there to be consequences. Unfortunately because of the price of energy and hour reasonability to the planet this is the way we have to go
Air tightness and moisture vapour tightness are two totally different things. A vapour barrier still allows moisture vapour to pass through it but at a controlled level. This is why you don’t use a DPM as a vapour barrier which blocks any moisture movement.
When doing a warm roof do you need to connect your wall vapour barrier to your roof vapour barrier to make the room airtight and if so, how? With it being on the other side of the deck?
Realistically you cant but you can get close and close is all you need Ill be showing that soon on the test rig
@@SteveRoofer oh great, I look forward to that soon I hope :-)
Could you share a link or recommendation of a product for the VCL you used on the ceiling please?
Novia 1200 Vapour Control Layer 100m2 Roll
Have to admit vapour barriers being on the inside of the structure never made sense to me when working in the states or back in the UK. Vapour control layers on the outside of the structure make far more sense and just having an air tight structure where the passage of air is controlled on the users terms. The difference with being back in the UK is the general construction isn't a reduced height warm room with a cold roof over it.
I think warm roof with cold roof over hte top is the way to go but hight being the problem
@@SteveRoofer While I was working there they do a reduced height construction warm room + ventilated cold roof. LVL's and engineered joists are generally the go-to for it but it near enough takes up the same space plus 1-2 inches. NA is massively ahead in wooden framing building techniques though compared to the UK and the general level of air tightness is much higher on the new builds back in NA than new builds here in the UK.
Hi,
What should be the thickness of insulation board for my garage cold roof?
Depends on if you need to meet building regulations if you need to build to building regulations thickness is 150 mm now
Hi Steve, I've always wondered what it is about a thick gauge dpm which makes it unsuitable as a VCL ?
Nothing to do with how thick it is
DPM is not CE approved for vapour barrier use and must not be used. It is a totally different product.
@@_Mark_H Yes exactly my point
Hi Steve, thanks for this video,, can you help? we need to insulate a large wooden shed, please advise the best way to go abot it... ONLY THE INSIDE. ITS GOT A PITCHED ROOF AND WALLS ARE 2.5 METERS HIGH ,,,Thanks.
if you do not want to spend a lot of money just use Rockwool with a plastic AVCL on the inside I would not be to fused about the quoity of the AVCL for a shed
imagine how angry this guy gets when you don't wrap the chicken leftovers in enough cling wrap.
That's good
Can you make a warm roof system with a slope roof. If what’s the max slope ?
I think that a pitched roof stopes being a pitched roof when you get down to 12 degrees Ill have to look it up. However theoretically if yo made a roof with say 30 degrees pitch the same as a flat roof what's the difference? The only thing I can say is that hot air rises and at the top of the flat roof you may get a collection of moisture if you are going to get any problems at all.
@@SteveRoofer great on sight thanks
what's always puzzled me is how a vapour barrier works when we put hundreds of screw holes in them when fixing our plasterboards.
And worse of all is the 3 or 4 missed screws that happen that won't even have a screw in it to fill the hole.
Butyl tape should be used.
Yes I'll Be showing that in another video
If you just put metal tape over the seams of the foil backed insulation board (covering the studs/rafters too), wouldn't that have the same effect as using a vapour barrier?
yes possibly but can you guarantee that you get everything every hold and divit !
I'm doing my bathroom with ridgid insulation and just foil taped every gap joist I could ....I rang someone from celotex and they said the foil does act a a vapour barrier....I really did find it confusing looking on the internet for the best way forward
@@SteveRoofer I asked because that's exactly what I did with a vaulted bedroom last year. I was meticulous with the tape - probably went a bit overboard. So when I saw your video, it had me thinking. Love the videos - I've learned so much from them, especially as a DIYer.
@@eddddd123 Ahh, good to know, as that's exactly what I did last year.
@@pdgnews Yes Paul it should be fine.....I did put thin plastic membrane around shower area just to be safe and alot of ridgid insulation was doubled up so I'm hoping it will be fine.....what gets me is you spend all this money on insulation and then put a big hole through the wall for a fan lol....feels like your totally defeating the object 🙂
maybe not your field.. :) but do you need a vapor barrier if you're insulating floorboards?. My floorboards are suspended on joists and then there's just a big gap before the dirt underneath. Lots of cold air comes up through the floorboards and i was hoping just sticking insulation in between the joists would help (leaving space underneath for air ventilation). Sorry not roof related ;)
p.s. great videos, I'm watching a bunch just out of interest at this point!
Isn't it good to allow the vapor to escape the building, how is it good that it cannot escape?
I have a brick single skin garage and planning to insulate:
1.BRICK
2.Breathable Membrane
3.Baton walls over Breathable membrane
4.PIR
5.Vapour Barrier
6.Plasterboard or Timber sheeting to finish - No air gap Is this correct?
Hi Darren, I'm doing exactly the same thing and it sounds correct to me. Although I am going to hold out until the summer until I do this.
It's the cold fibre glass roof that I'm going to struggle with.
Let me know how it goes 👍
So it looks to me as if you are doing this from the inside. If I was doing this from the inside I would be using one of the new multi foil products as they're amazing. I did exactly what you're talking about on my garage multi foil on the inside that also acted as the vapour barrierOver batons on the brick wall job done fantastic acoustically internally and thermally internally
if you have to multiply a MNs/g value by 0.02 to get a SD value, then why is Alutrix 600, according to the manufacturer, >1500 SD value and yet is 4,310 MNs/g?
I’d rather live in a draughty house than a mouldy house.How many builders can you trust to do this work properly?Great videos btw.
Thanks
You put the vapor barrier at the inside of the roof, and the outside of the walls?
It always gos on the worm side of any insulation
@@SteveRoofer thank you.
Does using foil tape on top of the kingspan do the job?
Possibly If you can make it air tight and if its going to last the lifespan of the building !
@@SteveRoofer Why on earth don't PIR manufacturers would publish spec of the foil facings? I'm having to buy and install a seperate vapour barrier because they don't. If they stated their sd value/MNs/g, emissivity etc, then maybe all I would need is lots of alu tape.
With old houses built in 1900. No cavity. 9 inch solid wall. Would you say batten and then put insulated plaster board over it? Or is it silly
are you talking about walls or ceilings?
@@HampsteadBuildersLt brick walls
@@tommyb5244 no not silly its the way its done ad a DPC (damp proof course) under the batten.
@@HampsteadBuildersLt so battens drilled to the wall with a dpc under. And and good insulation board with a vapour barrier behind it?
@@tommyb5244 yes plasterboard avcl insulation battens dpc
😂👍🏻😂
I'm going to use thermaquilt on my walls as the only vapour barrier. They say it acts as a vapour barrier and insulation in one. What do you think?.
don't know anything about it whats is Sd value ? also make sure its airtight
@@SteveRoofer its actually called superquilt, and it says vapour resistance 1569 MNs/g.
@@benrichards1 so a Sd value of 311 thats good
@@SteveRoofer thanks for the reply.
BS5250??
If only they produced PIR insulation at lower depths with higher u values. Or mineral slabs and adding a foil barrier to the outside prior to boarding roof, dormer to reflect the UV. I don't get the vapour barrier internally approach. The system is too rigid and needs adapting at times. Too many houses thrown up with a load of PIR and not enough thought about how the house needs breath.
Agreed
Just dont put downlights in your ceiling on a cold roof. There are very good led light strip systems out there now. No need to cut holes in a ceiling anymore.
The good thing at the moment is that we have lots of different lighting options, so realistically with forethought there is no reason to cut into the Air Vapour Control Layer (AVCL)
I can’t help thinking we are causing more problems than we realise. In modern properties there is no air movement, extractor fans don’t do much as the building is so air tight they don’t pull in fresh air. Both my son and daughter live in new builds and when they stay with us for a few days they always say they feel so much healthier . New builds feel more stuffy.I live in a 1960s house . Even my builder says don’t ever get the cavities filled . He said it took thousands of years to invent the cavity wall and 50 or 60 years to decide to fill it. I do have plenty of insulation in the loft but that’s as far as it goes. It might cost me more in heating and not very green due to less insulation but at the end of the day my health is more important than all this seal everything up attitude..
Yes all this air tightness is going to be a big problem
Trickle vents and open windows
Open the windows when needed
heat recovery ventilation remedies this, but can be expensive
After being in the building trade for over two decades, I wholeheartedly agree!
Would you advise to foam any gaps?
Any foam we use cans as its easier we have access to large canisters with big guns but they are never in the right place at the right time so we use the more costly way and use individual cans we can go through 24 cans on one roof that around £200 in foam alone
@@SteveRoofer thank you for reply. Yes not cheap eh.
Vapour barrier moisture barrier seems to be abit of a buzz word these days , why would you want to keep moisture in ???
keeps the moisture away from rotting the timber
So the moist air doesn't condense on the structure and rot it!
We insulate a lot now days thus stoping the transferor of engage and taking with it the moist air so things have changed
As clear as mud.
Is air vapour barrier breathable ,
You would not say its breathable in fact its probably best to say its restrictive
Air permeability and moisture vapour permeability are completely different things. The term breathable is very misleading in the construction world.
This is an interesting video but a lot of talking for not really providing an answer at what to use among all the product.
What’s next can’t wait !!! Become an online boss > Promo>SM!!!
More coming at 5 om tonight
What a con
Can you explain ?
@@SteveRoofer there is absolutely no need for one of these things what so ever
Everything is a con when you don't understand it
@@klaeLIFE i understand that it completely unessesary
@@adamcunningham2511 please explain so we can save the industry wasting so much plastic