Sweating and mouldy New cold flat roof

there I've been sent some fantastic photographs from a customer who's got a sweating roof this is the roof that he's built he hasn't finished the build inside yet and luckily enough for him he hasn't and already I can see interesting problems on this roof only one air break here but let's move on this is what it looks like inside at the moment you can just see the insulation running across here and of course we look on the outside here no Erik's you would think that it's no air vents you'd think that it's a warm roof looking inside insulation down below so this is formed as a cold roof we look again more more damaged we're looking inside this is where it butts up against the original house and again more internal sweating so you know what's the problem the problem is it the the way that it's being constructed first of all this is quite nice detailing if you look at the way he's nicely cut all of this in all the way around that's absolutely great foamed it or sealed it all up really nicely that is cut in lights into it and it's not airtight anymore so any moisture down below is gonna move up then we've got to be fed this extension hasn't been finished yet so there's probably a lot of them a lot of wet brickwork and a lot of moisture in this roof that's gone up through all this and it's gone and it's condensed on the back of the OSB board which is on the other side of this but the way this gentleman was going with this roof seemed well is definitely wrong he needs to increase the ventilation but luckily enough he didn't get too far and he's taken out a lot of the insulation for us to be able to see and learn from his mistakes now interestingly enough if you look he was thinking of taping all the joints and not putting a vapor barrier up which really is just is not the way to go you're gonna need a vapor barrier put up there in fact if I go back to this picture here the vapor barrier needs to be continuous starting from the wall sealed to the wall running across the whole of the bottom and up the side of the light well the vapor barrier has always got to be on the inside of the insulation and it's got to be sealed and that vapor barrier is also stopping the air from moving from the inside outwards because we're there you're going to get the transfer of moisture as well so we've seen this photograph we go over to this one this is where the extension backs up against the house and we can see the end of the rafters just here where they've been cut off he needs to make sure that there's good ventilation from inside this area that will move up into the cold space above his loft insulation and he needs to make sure that there's good venting inside the loft above there and again can't have the holes cut through with the lighting now if we look at this there's a trimmer that runs through here which is stopping the flow from this end of the roof running right the way across to the other end of the roof so realistically if he was to cut holes into the furring that runs across here and the FIR winds quite nice and fat at the back of the roof and so he's got a good opportunity of cutting some nice big holes in here so that any air that flows in here can go across side woods and of course at the very the other end the roof there and the other end of the roof there he can also increase the ventilation so that can blow through that way and that can blow through that way now we're looking out towards the back garden and you can see the uPVC fascia edges there it's not being fitted perfectly tight up going to the bottom of the OSB board here however realistically that gap should have because there is a gap there some kind of fly screen to stop flies spiders and things like that getting inside but I know because I'm going to show you in a second that down below on the soffit board there's a nice vent that runs all the way through now a good part a good detailing that he's got here I can see this glue which is dripping down the side of this timber here and that means that his glue the OSB onto the board onto the joists here which runs through which is not often done but when it is done makes the roof unbelievably rigid it stops what's called a slip on the roof which means that it's far far stronger and more stable so that's a lovely detail we can just see the thinner edge of the furring coming down here and he could still cut out sections of there so that he can get cross ventilation running right away through from right to left at this point because he's gonna have good ventilation coming up from the front he's also going to make sure that his insulation which this assume is gonna be a hundred mil in thickness so it's going to come halfway the height of this comes all the way down and and goes over the top of this wall plate and then you can foam along the bottom it must go at least 50 to 100 mil over the top of the wall plate so that you can continue the thermal element of the wall up and then across into the insulation of the roof we're looking at the other end here we've already seen how fat these are and here we can see there's loft insulation there that needs to be moved back a little bit further now looking from the top I know he did this in conjunction with his next-door neighbor so this is someone else's roof over here so we're only concerned with this but one of the things that comes the light here is the color of this timber this timber is too bright to be a treated timber and all this should have been built air of a treated timber nevertheless it's it's a nice job and I've also I've talked to him about this and he's going to treat all of this from the inside with a special treatment so all is not lost but what would have been the best thing to do on this roof would have been to put some battens at this stage going across from left to right every 400 right away across this roof then putting the decking on top that way he would have increased the cross ventilation everywhere because as I've just said you there's no cross ventilation here because this is a blind the each one of these is blind at this end there's no way of getting venting to it so you've got movement the air coming in that way but it won't move in if it's got nowhere to go hence why chopping out bits at the top and on this chopping out bits at the top there means that any venting which is running up there in there can blow up that in and come this way vice versa and all the way around there now on the outside here some lovely detailing detailing I can see a vent there and I know there's a vent going down the side now the vent going down the side actually there's a vent anything because you've got joist ends here and there's no joist ends here you've got one joist tight against the wall so to increase the ventilation again if he was to cut into that top of that joist furring goes across he can make this one thin across and into there which will just help increase everything that you can do to increase the ventilation on a cold roof is always going to help this is at the back that's a lovely detail when the walls rendered that's all going to look lovely and he's got a nice big airflow going in which can go around this is the vent there on the side that's great as well so this is the roof when it's finished and it's got a lovely fall you can see the fall on there everything looks great this just hope that when he did the upstairs here he turned this around with the the roof finish that he's got and he put these on top afterwards so that there's a good overlap on there but you know what a lovely roof it's a shame that he didn't get it right from the very beginning but it's salvageable hopefully this helps speak soon

Channel: Steve Roofer

Views: 431,612

Rating: 4.8494306 out of 5

Keywords: cold flat roof, new flat roof, flat roof insulation, flat roof construction, firestone epdm, vapour barrier, liquid flat roofing, warm roof vs cold roof, vapour control layer installation, flat roof problem, cold flat roof ventilation, insulating a flat roof, new flat roof systems, new flat roof installation, roof ventilation, glass fiber grp, warm roof construction, cold roof vapour barrier, cold roof insulation building regulations, New cold flat roof sweating and mould

Id: LL2-8RXSYKc

Length: 8min 35sec (515 seconds)

Published: Sat Jan 18 2020