Why Do You Have Condensation in Your New Roof?

[Music] hello i'm roger bisbee from the skill builder channel and previously on this channel we did a video about roof space ventilation and moisture build up and so on and we had quite a lot of questions about that and the thing that really confused a lot of people is whether they needed to ventilate a roof space or not and this vex is a great many roofers as well who think that by putting in a vapor open breather membrane as they're called that solves the problem and they don't then need to ventilate the roof space and of course even building inspectors are slightly confused by this whole subject so what i'm going to do in this video is to try and shine a light on it and bring a bit of clarity to the subject and hopefully we can work out what kind of ventilation if any you need in your roof space we used to have ventilation into the eaves which would come in on both sides of the roof through either a continuous strip or some holes in the soffit and that ventilation would blow over the roof and hopefully find its way either out the other side or if you've got ridge vents up into the ridge and away which is a far better arrangement than trying to get it to go back and over if you've got a wind direction here you've got wind blowing on the roof there wind is blowing through here and on the other side of the roof you've got a negative pressure zone you've got suction and therefore you finally got a vacuum when people talk about roofs being blown off very often what's happening is it's rather like an aircraft wing the wind is whistling across the top here and it's creating this uplift on this side so that actually what's happening is the tiles are really getting sucked off the roof rather than just blown off it and that's what we used to have and it worked very well indeed except for one thing and that was that having all this cold air blowing across the top of our insulation meant that it cooled the roof space down considerably so although it cleared the airborne moisture we had this cold air rushing across the top of the insulation and maybe you've got something like glass fiber in there or something else but obviously as the air gets through and you've got this suction going it means that that air is cooling that insulation down which is not a great thing the other thing that's happening is that because you have this air blowing over the top this vigorous air circulation ventilation going through the roof space you get air being drawn up from the house with this sort of vacuum effect that you've got here if you like the air is rushing over and it's drawing air up and the air is coming in through all the nooks and crannies around your windows your floor balls and everything else so you've got this air blowing over the top you've also got air being drawn up from the house being sucked up into that roof space around things like the loft hatch if a loft patch isn't particularly well sealed and around light fittings even worse if you've got down lighters in there but anywhere basically even around pipes and cables anywhere that the air can get through it will carry through and with it it will take moisture and this is all about moisture so when we increase our insulation we decide that we want to put in some more insulation we're going for the modern standard say 200 millimeters of insulation up there what very often happened is that people blocked up these air inlets here and that meant that this roof space was no longer ventilated properly but of course we still had all this moisture escaping from the house into that cold roof space and because that cold roof space is now colder because we've put more insulation in there we find that very soon we were getting moisture droplets forming on the underside of the roofing felt and dripping down on all the things that we got up in the loft and even when it got really bad say in the winter when you've got the heat on and of course when you've got heat on you've got warm air which has got more pressure on it and so the pressure differential is dragging that moisture out from the house and it's all going in there the moisture by the way is what we're creating from cooking from breathing from drying our washing from just basically living you've got all that moisture going up there it's condensing on there it's dropping down and in some severe cases you find that you've even got damp patches appearing along the ceiling especially at the edges and you get mold and the whole thing is just a nightmare what they try to do is they try to balance this idea of having more insulation in the roof space and getting rid of the moisture without over ventilating the roof space and the way that they did that was to put on a membrane which is a vapor permeable membrane now these are often called breather membranes but breathing membranes are actually for walls that the actual official breathing membrane is for a wall and these are what we call vapor permeable vapor open and they can also be air open and if they're air open it means that they will allow a certain amount of ventilation certain amount of air that's blown through to go through the loft and do a great job in ventilation the problem is that not all membranes are equal some of them have a higher resistance to moisture than others now the membrane is great because what it's supposed to do is stop windblown rain and snow and things like that from getting under the tiles and leaking down into your loft so they do a great job in doing that but they also need the moisture to escape through them so if you get yourself a good breather membrane and what i would say the measure of a good breather membrane to me is one that's made up of different layers different pliers maybe three ply and the idea of that is that you've got this wicking surface on the membrane so that when you're getting excess moisture coming up from the house when it's cold day when you've got a lot of heat coming up from the house you've got a lot of moisture coming up it's actually hitting the underside of that membrane and it's soaking in it's being absorbed by that wicking layer in the membrane and it's holding it there and then as the membrane dries out more of it is drawn through so basically that is the best kind of membrane you can get and it will cope with sometimes very high levels of moisture the drawback is that it very often costs quite a lot more money rather than being able to pick up a membrane for say 40 quid you might even be paying 120 pounds for a 50 meter roll of meter wide membrane to do the job but it is an investment the only trouble is that roofers who are on a price they're trying to do your job cheaply they're trying to make as much money as they can which is understandable they're looking at these materials and they're thinking should i pay 120 pounds for that membrane or should i just put them in one for 50 quid and they don't always know that that membrane won't work in that situation one of the reasons they don't know is because roofers don't like going into your house so the one thing they're not going to do is they're not going to examine your ceilings to see if you've got any kind of vapor barrier across that ceiling which would be polythene sheet is put on before the plasterboard goes on in other words you've got the ceiling joists here you've got a layer of polythene there and then you've got the plasterboard there so that anything that migrates through that plasterboard hits the polythene and can't get through now that's a vapour barrier and that's supposed to be fitted in new buildings sometimes it's done with a fallback plasterboard but you're supposed to have that really tight nice level of vapor protection running down the side and joining up with the walls but it's not always done and the roofer who's on the scaffolding who never wants to go inside the house is not going to go in there to examine whether you've got a polythene membrane in there or anything else or whether you've got lots of leaks around the loft hatch and so on and if he does see that situation he may think you know what in this situation we need a higher grade membrane in other words we need a wicking membrane which is going to cost 120 quid so if all he's doing is saying i'll buy you the cheapest membrane i can now fit it it's not always going to work out for your particular house sometimes it can sometimes afford liquid membrane is exactly what you need but this is the problem that we're up against we've got this situation where it falls between different trades when they're building a house the roofer isn't interested in what's going on with the plaster ball or the vapor barrier and of course those guys aren't really thinking we don't know what the roofer is going to fit in the way of membrane so it's a question of having a little bit of knowledge yourself and asking the right questions now we're just going to put up a few links to some membranes you can see what they are you can see what the price difference is and you can see which ones comply and we'll see which ones can give you a very high level of moisture permeability so sometimes you can pick up a bargain membrane and if you're in any doubt check with the manufacturer to check whether their membrane is suitable now i was looking through the screwfix website for example i saw a membrane in there and it clearly stated that it does not require additional loft ventilation i thought well that's a very brave claim to make given the fact that they don't know what situation you got and i looked at this membrane and it's fairly cheap membrane but actually it was a three-ply membrane so they were dead right it should do the job but what i'm really saying is when you have that roof renewed you really need to go up and check a variety of different weather conditions go up and have a look at it in the winter going up and have a look at it and see that you're not getting any moisture forming on here because if you get moisture forming on the underside of here and it soaks into those rafters and it rots those rafters you've suddenly got yourself a very big repair bill so if you do see moisture building up in the roof space if you do see droplets forming on the underside of that membrane and it turns out that they fitted the wrong membrane the best thing you can do in those situations is to introduce more ventilation into the eaves and possibly a ventilated ridge which is basically a ridge tile which has got a bit of air path through there so that this moisture can escape through there and if that's not possible some of those little ridge vents that you get which are basically you replace the tile and put in ventilators you've probably seen the sort of thing sometimes they're quite ugly sort of mushroom things sometimes they're nice and neat flat ventilators but whatever you do if you see moisture it means you've got to increase the ventilation or you've got to fit some kind of vapor barrier here to stop that moisture getting up into the roof space and the other thing that you really must do is extract the fans make sure you've got extractor fans in the bathroom in the shower room and also down here in the kitchen and extractor cooker hood and things like that so as you're creating that moisture you're removing it as sauce before it has a chance to get around the rest of the house and do its worst the situation is made worse by the fact that we have double glazing we're draft proofing all round we're sealing up our houses and if that moisture can escape into the roof space it's really one of the only ways that it can get out i hope that's helped to clarify the situation it's a little bit rambling i guess and i could probably clarify it more but the thing to do is put your questions in the comments below and we'll try and answer those and don't forget we're going to bring back ask skill builder very soon and so if you've got a particular question that you want to ask us if you've got a situation with your house send us in some nice video pictures that way not upright and if you're interested in the subject you think you might have problems with moisture in your roof space check out this video [Music]

Channel: Skill Builder

Views: 39,917

Keywords: roof ventilation, vapor barrier, stop condensation, loft ventilation, condensation in the loft, loft vents, roof vents, condensation on windows, roof ventilation installation, roof ventilation design, roof ventilation system, roof ventilation explained

Id: kvsPIlPMSZ4

Length: 12min 37sec (757 seconds)

Published: Wed Nov 17 2021