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- 11 Sep 2021
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Hi
I have an old flat roof which is failing. The roofers have stripped the felt and replaced some of the OSB. Underneath there's a (to my mind, not well constructed - e.g. gaps in insulation/no foil taping) cold roof, using PIR (I'd guess 75 or 100mm). The roofers have put on a VCL and PIR (150mm) on top. I've included a mock up diagram:
I'm concerned that this isn't the right approach, as there's currently cross ventilation above the cold roof, which defeats the point of the new 150mm PIR. The roofer says the answer is to block the vents "the solution is to cap the air vents on the soffit below which is not a drama ! Timber or plastic over it". That doesn't really make sense to me ... Hopefully he's right. He's since added "No air flow needed with the warm deck. The air vents are doing absolutely nothing and never were as they're only at the front and no air flow to any point at the back".
Here's the cold roof before they put a warm deck on top. It has soffit vents on the front side - the roof is a rectangle (c. 6.5m x 4m) - the vents are just along one long edge. The other sides join a cold angled roof.
I have an old flat roof which is failing. The roofers have stripped the felt and replaced some of the OSB. Underneath there's a (to my mind, not well constructed - e.g. gaps in insulation/no foil taping) cold roof, using PIR (I'd guess 75 or 100mm). The roofers have put on a VCL and PIR (150mm) on top. I've included a mock up diagram:
I'm concerned that this isn't the right approach, as there's currently cross ventilation above the cold roof, which defeats the point of the new 150mm PIR. The roofer says the answer is to block the vents "the solution is to cap the air vents on the soffit below which is not a drama ! Timber or plastic over it". That doesn't really make sense to me ... Hopefully he's right. He's since added "No air flow needed with the warm deck. The air vents are doing absolutely nothing and never were as they're only at the front and no air flow to any point at the back".
Here's the cold roof before they put a warm deck on top. It has soffit vents on the front side - the roof is a rectangle (c. 6.5m x 4m) - the vents are just along one long edge. The other sides join a cold angled roof.
