Stop Condensation in Your Loft ~ Ventilation & Vapour Control

hello i'm roger bisbee from the skill builder channel and i would like to talk to you today about them in fact the very specific type of them vapor and vapor control why do we want to control the vapor well as you've just seen on this board vapor condenses and what we don't want it doing is condensing in the wrong places because if vapor condenses in the wrong places it leads to mold mildew dry rock some of you will have probably got a loft an attic a place doing nothing at the top of your house sometimes when you go up there you find that there's lots and lots of little droplets of water coming off the sarking felt on the inside of your roof and the reason it's getting damp is because moisture is traveling up from the house into the loft the moisture is created by us doing things like breathing having a shower you create moisture everybody in the house creates moisture so what you've got is got moisture that's drifting up because it's warm it's in the air it will vary according to the time of year as well but that humidity is hitting the plasterboard ceiling here one of the places it can get up into the loft is around the little loft hatch that we've got here because if that's not sealed all the way around effectively then you've got air escaping through there you've got little giraffe going through there and that air contains moisture you might also have some lights here and you might have a cable coming through there and that cable is allowing a little bit of air to come through and that is allowing a little bit of moisture to come through now you might think they're small things but they all add up you might also have some pipes because you might have a tank in the loft your tank might not have a lid so it's a bit of evaporation coming off there but also around those pipes they weren't sealed up properly when the plumber put them through the ceiling and so you've got a little bit of moisture that's coming up through here so you seal off all those points which is a good thing to do but you've still got moisture in the the roof space where's that moisture coming from well believe it or not a lot of it is actually traveling through the sheet rock it's traveling through the plasterboard it's migrating even a solid sheet of plasterboard with no holes in it or anything like that can let through about half a pint of water over the course of a year now that doesn't sound a lot obviously but that's only one sheet of plasterboard so what have we got on the ceiling we've got maybe 10 sheets of plastic ball on the ceiling so let's have a look at that half a pint of water time five pints so we've got five pints of water which is actually just getting through the ceiling on its own so what do we do before we put the plaster ball up we put in a vapor barrier which could be a polythene sheet or it could be something a little bit possible because they do actually sell polythene sheep which is more expensive because it's called vapor barrier but actually it does work better because even polythene sheets sometimes can let a little bit of moisture through so you've got that and it's very very important that when you do that you tuck it up on the sides here that you seal all the joints through there then you make a good job of sealing any points where the cables the pipes anything else comes through and we keep that moisture from migrating up into the roof space and we do our best but we're never gonna completely succeed at that game because for one reason and another maybe it's you're going up into the loft all sorts of other reasons you may get a little bit of moisture up there but the best thing to do is control it at this point now the other way you can control it is plasterboard which is foil backed and that is a vapor control in itself that foil back that silver foil on the back of the plaster ball stops the moisture from migrating through the plasterboard other than that there are a few joints and things like that but you get the idea we're stopping most of the moisture getting up into there so that condensation that we got on the roof space is much reduced on the underside of that sarkin felt it's not bro so pronounced now if that sucking felt is the old fashioned type the bitumen type then it will just condense because it can't go through but now what we've got is wonderful things which they call breather membranes so when we put the tiles on the roof and we put that under tile layer in there that sarkin felt that membrane instead of using something like bitumen which was impermeable we now use a fabric which allows vapor to go through but repels water so as the water falls from the sky if it gets through the tiles if it's wind blown or anything like that it then runs down the outside and hopefully safely into our little gutters there all the moisture that's in the loft hopefully can escape through the permeable membrane and away it goes now people are relying on permeable membranes completely these days and sometimes they're finding that they've still got problems so if you look at an old house if you look at an existing house and the roofer comes along he's going to put a new roof on for you and he says what you need there you need a permeable membrane we're going to stick that on they always stick that on now because they're much lighter and it's got quite cheap actually so they always put that on and then they say yeah you don't need any vents in your roof you don't need any little places for the moisture to escape because you've got it's wonderful breathing membrane on there and that's taking care of any moisture it's breathing basically it's letting all that moisture out which is absolutely lovely and of course as it warms up in that loft and it dries out and that vapor is enhanced if you like if it's sitting on the underside of there and it warms up it will go through a lot more effectively but obviously in the winter it doesn't go through quite as well because what it does is it goes up through the loft through the insulation you've got a nice layer of insulation here goes through the insulation and it hits that membrane and it condenses the water droplets appear on the inside now there's a wonderful fabric called gore-tex that i happen to be lucky enough to own some of and i use it for walking i use it for all kinds of things and even for cycling and when you start building up a bit of a sweat when you're going up the hill and you start sweating profusely then that moisture is leaving your body at a rate and it goes through the pores in the gore-tex because you've got tiny little holes in the gore-tex and the moisture can get out but the rain can't get in absolutely wonderful thing when you start producing too much moisture and it's cold and that moisture starts condensing on the inside of the gore-tex then it's got a wick through it's got to find its way through that fabric to the outside and if it's cold and you're sweating a lot it's not going to do it as well as it might if you were just gently ambling along and it was a slightly warmer day so there is a limit to what all these things can do there's a limit to what these vapor membranes can do that they have the permeable membranes that they have on the roof and the more expensive ones have got several layers of fabric it's a non-woven fabric but it's got loads and loads of microscopic holes in it because of the way it's constructed you've got an absorbent layer if you like on the inside and that takes a little bit of the moisture holds the moisture and allows it to evaporate in its own time so it will just hold a bit so that's a much better type of membrane than the very cheap ones you also get something called open air membranes you get something which is actually the air can pass through very very freely both ways so it's almost like having a ventilated roof space it doesn't cut the draughts out because it still allows on a windy day air to flow through the loft and take some of that moisture away so there are various standards for all these things there are various grades but the whole point about it is that if you've got a good membrane if you put a better quality membrane on there you're likely to have less problems but it does depend upon you having a good vapor barrier here to stop that moisture going up if you've got an old house and it's got old lava and plaster ceilings the lime plaster and the moisture is going through it then i'm afraid that you may still need to put some little vents in the roof to improve the ventilation the vapor will also travel through the walls even if you've got brick walls it's cold outside and it's warm inside and as isaac newton said heat will travel to cold it won't travel the other way round so that's a very very important thing to remember our heat is traveling too cold now when it's hot outside and the hotter it is the more moist the air is likely to be in other words warm air can hold a lot more moisture than cold air so when it's hot outside and it's muggy and we can feel that moisture in the air and you've got air conditioning on the inside it's actually traveling the other way if we've got something like a timber frame house is we need to put that same vapor barrier there inside the wall on the inside on the warm side of the house because if we stuck it on the outside it would allow the moisture to travel through the insulation whatever we got in there in a way of insulation and it would hit the cold area which would be on the other side of the insulation so we've got a bit of insulation in there if that moisture was allowed to travel through there it would hit the cold on the other side of it and it would condense on that inside of the outside if you like so whatever you got there cladding or even brickwork or something else you get moisture condensing on there so it's very important that we try to stop it before it gets through the wall so that vapor barrier the positioning of that vapor barrier is very very important it's also very important that we join that vapor barrier to the one in the ceiling we don't leave any gaps we do a very good job because the devil is in the detail it's always in the detail moisture is going to escape it's going to escape through all those little bits and pieces so we do a good job of taping and sealing all that vapor barrier all the way around the house around the windows round the doors anywhere where it's possible for a bit of moisture to escape through the fabric of the building and find its way into that space the other side where if it builds up it can start to cause rot and all kinds of other problems mold and you name it so we don't want it we want to get rid of it so that's just basically the principle of a vapor barrier and vapor control but i did say to you that in the hot weather you can get exactly the opposite happening so you get a situation where this is the cold because we've got air conditioning and this is the hot so isaac newton is telling us that that hot is going to travel to cold and of course it's going to get through the insulation and when it gets through the insulation it's going to hit the cold surface on that side so if it hits the cold surface on that side it then condenses you get condensation forming on the inside of that vapor control layer you also get it soaking all the timber stud work and the insulation in your house so what do you do in a situation like that you know maybe you think okay i'll put the vapor barrier on the outside and maybe that will help and therefore it'll stop the vapor getting through before it goes through which is wonderful it's wonderful in the summer but what happens in the winter in the winter when that is now cold and if you think of some places you think of canada where they get great extremes on the prairies of very very bitterly cold winters but very hot summers and that situation is likely to change season by season so putting a vapor control barrier in a situation like that is kind of a no wind because at some point in the year it's going to be working against you so there are people who say well the best thing to do not put a vapor barrier in there at all to actually leave it out and to just let the free passage of moisture go through the wall in whichever direction it wants to go through but at least it's not being trapped inside you know when it gets inside we need to get rid of it we need to dehumidify it which it will do to a certain extent because as soon as it hits that cold surface that's what's going to happen if it gets to the outside it's just going to disappear harmlessly out to the outside provided we haven't stuck something on the outside of the building which is a non-breathable if you like something like a pvc siding or cladding or something like that there isn't an ideal answer what we're trying to do is stop the majority of that moisture from getting in and harming the house and of course the other way you do it is you build your house from things which are not going to be affected by moisture so if you're having timber you have pressure treated timber which will be less inclined to rot but that's one situation but of course you've got a lot of people who live in houses with flat roofs unfortunate people because a flat roof is never going to be as good as a pitch roof simply because water runs downhill now here you've got the same situation you've got the same bloke or his brother and his brother is still washing he's still doing all the things his brother is still breathing hopefully so he's still creating moisture in this house now that moisture is going up into the flat roof this time so he's got a layer of insulation in this flat roof and if he's got it like that this is what we call a cold roof the insulation is all stuck on there and this is very important that when the insulation is stuck on there we want to have some kind of ventilation going through in these these joists so all those joists need a hole in them if we try to get cross ventilation or the they've got holes in the front here in the fascia which allow the air to go through but whatever happens we want air passing through there and coming out there all the other way around doesn't matter but the idea is that any moisture that escapes up there it hits the cold side it hits the cold spot in here and we need to get rid of it that same thing as the pitch roof exactly the same principle but on a flat roof so what we do on a flat roof we try still to put a vapor barrier in here because we want to stop the majority of moisture going up into that flat roof and one thing we don't do on any of these roofs whether it's a pitch roof or a flat roof is put down lighters in because as soon as you start drilling the ceiling to put your little down lighters in and the down light is even the fireproof ones have got ventilation because they get a bit warm and they need to vent as soon as you do that you've got basically an extractor you've got moisture that's coming up here you've got a little light in there which is slightly warm less so with the led ones but still slightly warm and of course the moisture is just traveling through there and escaping so how many down like this do people put in their house well sometimes you go to a kitchen and you see 20 down lighters in the kitchen so that's 20 spaces through breaching that vapor barrier where you can get moisture going through to your roof and then suddenly you find you've got damp patches and you're wondering what's going on you think you've got a leaking roof you call the roof around he looks upstairs there's nothing wrong with your roof it's probably what they call interstitial condensation so if he's a clever guy he says to you we'll increase the ventilation across there and we try to do something about those down lighters use a different type of light that would be the the sensible thing to do but of course people are wedded to these ideas of them like just they love them and if they they love them then they've got to also love the fact that they're rotting their building to bits more and more these days is we have what we call a warm roof now it is generally considered that a warm roof is better than a cold roof sounds logical doesn't it really i mean who wants a cold roof but the idea of a warm roof is that we've got all our joists here we've got our plasterboard there and we have a another piece of decking going across the top another bit of osb 3 or whatever plywood whatever you're going to use going across there and then we put the insulation on the top and then we put another layer of decking on the top and then we put on increasingly a big grp or something like that but whatever you want to put on single membrane or whatever but that membrane will go on the top now if we didn't have a vapor barrier the vapor could still come up through here get through that insulation and appear on the underside of the waterproof covering whatever that was as i say whether it's a single ply membrane whether it's grp or whatever it is what we'd end up with is moisture that is trapped in here under there and it will start rotting that and again we get spongy bits you go up sometimes and it's like weetabix up there you can just push your foot straight through it often people find out they go up there to do something and they just put their foot through the roof i think oh my goodness the way we get around this to some extent is we put a vapor barrier in but we don't put the vapor barrier in there because what we want to do in this particular case is to keep all that space that's warm all that space is heated now we don't want to start putting insulation in there even though you think oh that'd be a good idea i'll put some in there and what they might call a hybrid roof where you've got a little bit of insulation in here you've got a bit of insulation there but of course that's a problem because what you then get is you've warmed up this lot but you've created a slightly cooler surface there so even though you've got insulation on top it's a relative thing it's a bit cooler than this so as the water as the vapor carries up through the through the ceiling and so on we've still got a ceiling in here by the way plasterboard ceiling so that plasterboard is letting through as we said maybe about half a pint of water per year per eight by four sheet we still need to watch it and if we've got any kind of breeches in there any kind of cables running through there we've still got this situation where we've got some moisture going up there so what we need then is we need to put our vapor barrier on top of this piece of decking so this is a piece of plywood or osb like i said and that sits there that is within the warm area of the house and then we put in some kind of purpose-made vapor barrier in there so this plywood that's here is on the warm side of the building so that's not going to rot now any moisture that comes up it's going to get through the plywood it's going to permeate through the plywood and it's going to appear on there but it's because that's warm it's just going to evaporate it's going to carry on evaporating so we're not going to get too much trouble from that so we've got a vapor barrier here we make sure our vapor barrier is going all the way up there that it's doing a good job and that no vapor can get into our decking and onto the underside of there that's the important thing we don't want any moisture appearing on the underside of that membrane so everything is good the only trouble is that i have spoken to flat roofers guys who do nothing else but flat roofing and they go around to properties and they find that even when they've got a vapor barrier in there's still problems with moisture collecting on the underside of this decking up here so it's still managing to get through to some extent and cause some kind of rotting so there are guys who say you know what the best thing to do we go back to this problem that we got in say canada or whatever where we've got change in seasons and they say the best thing to do is actually not bother about putting that membrane in and just let the moisture go in there but also escape because as that warms up and it dries out it's got an escape route back into there so the problem with the vapor barrier is once you once any water gets through it you're trapping it if you like both sides so you have to make sure it's done really really well but of course the other thing you can do is you can stop the moisture in the house and the way to stop the moisture in the house is not to stop breathing not to stop showering or doing any of those lovely things that you like to do cooking and things like that but to put yourself in extractor fans here so that you're getting rid of the moisture as it appears you could have an extractor fan in there if you liked with a ducting that went out there but whatever it is you've got shower upstairs you definitely need one in there you just let all the moisture escape and the more you can do to get rid of the moisture at source the less problem you're going to have here so that would be my first piece of advice is take care of the moisture at source and then you won't have so much of a critical job to do here if it did migrate through if you found that you were getting a little bit of moisture through it could actually evaporate and not cause too many problems but there's always going to be some moisture basically you're never ever going to get rid of it totally but if you can reduce it you can save yourself having those horror stories where you find people with condensation because once you've got moisture once you've got condensation of course you've got mold a mold as we all know now is toxic it's not good for your health and you really don't want to have it in your house so we do everything we can to avoid the moisture from ending up in these cold corners where we don't want it that means we never dry washing in the house on the radiator as tempting as that is to hang your smalls over the radiator to dry them off it does create extra moisture in the house and that will create more condensation more than and this is of course a kind of condensation if you like it's a condensation problem but it's the unseen condensation now we've mentioned timber frame and all the rest of it but we also have to talk about brick and when we've got a brick wall here instead of having timber we've got a cavity here and we've got an inner skin and an outer skin that moisture is still going to migrate through that block work through that brickwork and it's going to get outside when it gets outside when it gets through that internal layer and maybe it hits a bit of cavity wall insulation that's in here some people love it some people hate it but if it gets through it's going to travel through that cavity wall insulation the place it condenses we call the dew point and the dew point in this particular case is the inside of the outside skin because that outside brickwork is going to be the same temperature on the outside supposing it was 5 degrees centigrade there or celsius it's going to be 5 degrees celsius on that point there so the dew point here would be on the other side of that insulation that's where it would be getting damp and that's where it would start to trickle down and hopefully safely drain into the bottom and through the foundations in a way or some people have a step damp proof course in here and they have weep vents and it trickles down there and it gets away there but if we don't have an impermeable layer on the outside if we've got brick work or we've got block work and we've got nice lime render or something that isn't really tight then a lot of that moisture is just going to carry on evaporating through the outer surface of the brickwork and of course as soon as we start sealing that up with non-vapor permeable layers then we do create that problem of we're trapping the moisture in not the end of the world because it can still escape to a certain extent down there but of course some of it will start to make the insulation wet and of course it gets worse if we've got driving rain coming in to that brickwork and soaking that brickwork so we've got water trying to get onto the outside we've got water coming onto the inside we've got saturated brickwork and of course then it begins to saturate the insulation and of course wet insulation is no insulation at all so then the next thing we find is we're getting damp patches on the inside normally where the wall ties are all these things are solvable best thing you can have is some kind of vapor permeable layer on the outside and that will solve the problem and there are plenty of products around now had some guy came on the other day when i was talking about stormdry and he said that is impossible he said that is complete bollocks he said that can't happen he said because there is nothing on this planet that can stop water coming in that will not trap water or water vapor going out and he is so totally wrong about that that it just beggars belief but this is what people do they come on they think they know what they're talking about and actually they don't there are loads and loads of vapor permeable products out there and all you've got to do is look for them whether they're in the form of breather membranes which go under your roof tiles or whether they're in the form of other coatings that you put on the building there are plenty that will allow that transmission of moisture and the reason they'll allow it is because vapor water vapor is very very fine indeed if you imagine it's steam basically and even though you can't see it in the air steam is coming off things even on a very cold day water is evaporating off surfaces all the time going up to form clouds obviously that happens more in the warm weather but in the cold weather it's still happening things are drying out just remember it's on the move all the time and what we've got to do is just try and be aware of it and control it i hope you found that interesting uh it wasn't a rent sometimes i don't rent sometimes i just talk and uh i talked about that and obviously there's going to be people who disagree with me on this they're going to be people who want to add their little bit and thank you very much and do feel free to comment underneath but also don't be surprised that if you talk complete nonsense i will try and challenge you on it i'm roger bisbee come back see you soon on skill builder we'll have lots more exciting stuff coming up and don't forget if you've got a particular damp problem we've got ask skill builder where you can send in pictures of your debt problem any video that you want to send in and we'll do our best to try and help [Music] you

Channel: Skill Builder

Views: 240,242

Keywords: stop condensation, vapor barrier, condensation in the loft, loft ventilation, loft vents, roof vents, roof ventilation, loft condensation, condensation in the loft space, condensation in the loft problem, vapour control layer installation, vapour barrier, warm roof construction, warm roof insulation, cold flat roof ventilation, interstitial condensation

Id: M5tyd3ayt80

Length: 27min 59sec (1679 seconds)

Published: Wed Feb 03 2021