Vapour barriers for roofs and walls explained

vapor barriers in flat roofs mainly cold flat roofs and walls i'm going to cover here i'm not going to do anything about warm roofs already done warm roofs before and the vapor resistance in one roof but what a nightmare if i was out there and i didn't know what i know now and i've done hours and hours and hours of research and it's a complete jungle out there if you get on the internet and you search vapor barriers you're probably just going to go by there's a vapor barrier and the cost of it and that's probably how you're going to buy your vapor barrier but it doesn't really work like that if you're building something you've normally got drawings if you've got drawings you've got specifications and if you've got specifications you should look at the drawing and it should tell you what vapor barrier but you know most i don't think i've ever seen a drawing that says use this vapor barrier and it tells you exactly which one to buy because no one likes putting a product down so you you're left there to go and choose one and if you choose it and it's the wrong one you actually are being held responsible for designing it because you've actually chosen something therefore you've designed it in which case you're going to be held responsible i would always go back to whoever's done the design and say which vapor barrier and make sure i've got it in writing so i want to answer the question which is asked all the time what would i use in a roof and what would i use in the walls now if we're using vapor barriers that are for a domestic use not for say swimming pools or something like that and i must go over to this look novia have been really great they've sent me through products and things like that etc i just got on the phone to them and talked to them and they're really helpful they sent me through loads and loads of stuff some of these vapor barriers and this has got an sd of an sd value of 4 000 for swimming pools um different scenarios where you've got really high vapor um transfers going through the walls not our normal domestic kind of scenarios this has got an sd value of 200. now the thing is is that i've converted all this to the sd values the sd values which you'll get on the internet if you're lucky they might not use an sd value they'll use something which is called mega newton seconds per gram and it's like well what's a mega newton second per gram and what is an sd value it gets really really quite complicated and different people use different ones so you might find this one costs x amount but you and you just don't know you've got to try and work all this out in between so for for this particular video i'm using an sd value and the higher the sd value the the the more vapor resistance the material is so this one being 200 i say those ones down there were 4 000 now if i was doing this ceiling in here and putting a vapor barrier in it if it was going to be a cold roof i would use this particular one and this has got an sd value of 130 now i've purposely put that hole in it because what i see is i see people put up a vapor barrier then they go and get a light fitting and they stick the vapor barrier up put the light fittings through it and you've got all this moisture going through and you go well you know it doesn't matter what the quality of the vapor barrier is if you've got holes in it and you've got moisture just transferring directly through the hole i mean it is all this or must get the right vapor barrier i must get the vapor if you're not using the vapor barrier and fixing it correctly and sealing all these holes if you cut holes into it and it's just not going to work now novia sent me through these things which are little samples of their tapes which come with their system again you go on the internet and you look at all these different products which are out there they very rarely tell you that you should be using all these different tapes and things like that with the product so that when you put it in it works here they sent me through some samples of some tape i've put this bit of tape on this particular area here i've got to tell you by the way this is a setup that we've got in the yard which i'm now starting to demonstrate and mainly teach the men as well but demonstrate different scenarios because it's very hard for me to do so if i'm not out on site all the time i spend most of my time now driving around looking at work that's gone wrong so we've got this part here and generally speaking the way that this system would work is that wherever you've got a joist or something like that you must screw through into that particular tape now when you screw through now look at that it's pretty good it's pretty cold out here as well when you screw it through to that tape which is this one here it's a butyl tape and it seals all the screw holes so everywhere that you're screwing through your plaster ball you've got to have that tape you're going to use loads and loads of this tape it's not just the cost of the membrane it's the cost of the tapes which comes with the system now when you overlap a tape say for instance this one onto this particular one here you must use an overlapping tape as well so everything is sealed and it's airtight everywhere and air tightness is what it's all about but after all they're called air vapor control layers and i've got to stress that i see this with this light fitting going through and it not sealed all the time now probably next week i'll do another video showing you with the insulation up here how the vapor barrier goes up and how the light fitting goes through it and how to do it correctly but that's not for this video i mean this is just this just this video is just to point out how hard it is to pick the correct vapor barrier now this particular vapor barrier as i said has got a an sd value of 130 this vapor barrier is the kind of thing that i would use around about an sd value of 130 for the walls and and you can use more you could use slightly less but i wouldn't go for much less than that you you it's a vapor resistance which is good for domestic use where you've got an internal temperature of approximately 20 degrees with relative humidity which is up to approximately maximum 60 percent but anywhere between 50 and 60 and sort of 53 55 is nice for an internal um uh domestic property now when we start talking about what we've put actually up onto the the walls sorry this one here i would use i've got to take this off of here and that's how good that tape is this one here i would use for the the roof up there without a doubt around about 130 but this one here is slightly thinner gauge and the thickness of the gauge everybody talks about the gauge i get people phone me up and they go you know i've seen this black vpc or whatever well it and it gauges 1200 or the gauge is a thousand or something like that the gauge makes no difference it's is it a vapor barrier and generally speaking if it is green the industry standard is green for plastic vapor barriers so when i go to a job and i'm doing a site survey and i see a black one or i see a blue one i know it's it's not a vapor barrier it's probably a damp proof course or something else now this one is only a 500 gauge where this is uh 1200k this has got an sd value of 130 this has got an sd value of 50 and this would be good enough for doing walls you do not need to have so much uh resistance in a walls now i live in the real world i'm going around seeing jobs all the time normally called in when they've gone wrong and i very rarely see problems with walls even when holes have been cut through and you've got plugs and things like that and you could get a lot of vapour going through you very very rarely see problems in the wall and that's because heat rises when it rises it takes the moisture with it so any of the moisture that's got through gets up inside the roof when it gets up inside the roof and gets through this and by the way at the moment this has purposely been put in incorrectly just so that we can demonstrate the different scenarios and at this particular point i'm demonstrating to you your moisture is going to get through this if it's not airtight it's going to accumulate in these particular areas here it's cold behind there and because it's cold behind there it condenses and runs down and this is the problem so all the time again i'm asked on the internet you know you explain all this but you don't actually say what is the um the correct way of doing it i'm telling you the correct way of doing it the most important way of doing all of this is air tightness if you used the wrong vapor barrier and it was airtight good chance it's going to work but it's not now if you know you know if you follow what i'm saying if you're using a better air vapor barrier up here i i would suggest around about 130 up here it's an sd value of 130 and it's done in meters 130 meters up there and an sd value of about 50 meters on the walls you're probably in the correct scenario for a domestic domestic use however go back look at your drawings get in touch with whoever's done it and ask them what they suggest that is the only way of doing it that is exactly what i would do otherwise you're going to get you you are designing it and therefore you're responsible for it so hopefully that helps people understand that the nightmare out there with choosing all of this it's a complete looking on the internet it's a comp it's such a model um and i just feel sorry for the people out there who um haven't got the um time to look it all up like i have and to work out and actually do it properly and if anybody needs any advice or anything like that please drop me an email and i'll do my best to help them thanks for watching

Channel: Steve Roofer

Views: 100,042

Keywords: vapour barriers, vapour barrier flat roof, vapour barrier walls, vapour barrier installation, vapour barriers roofs, vapour barrier garden room, cold flat roof ventilation, vapor barrier installation, installing vapour barrier on walls, vapour barriers in buildings, avcl for roofs, roof ventilation, roof ventilation explained, how to fix a vapour barrier, velux vapour barrier installation, vapor retarder, cold flat roof ventilation detail, Vapor barrier installation ceiling

Id: T_VPXB1FlBk

Length: 9min 57sec (597 seconds)

Published: Sun Feb 13 2022