Damp Roof insualtion

holdfast

Hi I have come across a case where the roof insulation is damp. The project is new and the rafters were fully filled with rockwool which is now slabed over and plaster except where I spotted this. They have used a breathable felt. Any ideas how to sort this problem would roof vents in the slates work.

sydthebeat

holdfast wrote: »

Hi I have come across a case where the roof insulation is damp. The project is new and the rafters were fully filled with rockwool which is now slabed over and plaster except where I spotted this. They have used a breathable felt. Any ideas how to sort this problem would roof vents in the slates work.

have they left a 50mm vented air gap over the breathable felt??

holdfast

No fully filled it the construction is kingspan 37mm intello membrane , 200mm rockwoll flexi and vapour barrier.

holdfast

The area I checked had no intello membrane and no slab yet. This could increasing the problem as where these are in place they will reduce the condensation. As the kingspan and intello membrane are vapour barriers. So the problem by that thinking is just confined to this area which is not finished. Would that be the case as this area has neither or is my assumption wrong (taking an assumption makes an ass of you and me)

Just had a little time to think about it but I think I well specify slate vents for this area anyway. ( as any civil engineer will tell you when all else fails big nails meaning over design it.)

sinnerboy

Holdfast what measures are in place to ensure air flow over the breather felt ?

A BIG misconception is that breather felts do not require ventilation - this is at best a half truth

You don't need to provide the 50mm vent space below the felt - but you do need to provide it OVER the felt ( as Syd did say ) - battens and counter battens

another typical failure arises when the felt is dressed over the continuous top- of-facia-and-behind-the-gutter vent strip . If you draped the felt over this - you admit air in to ? nowhere - because this space is stuffed with quilt in your case . In your case the felt must be dressed under the vent strip .

A possible retro fit job would be to install ventilator tiles - max 1750 c/c high and low . Use in line type - you don't see them from the ground

holdfast

I will go with the vent tiles and finish off the sealing of the building once the area that is affected has the damp insulation removed. At this poin the HRV and the vapour barriers should reduce the chances of happening again.