DIY Doctor UK DIY Forums

I had a leaky flat roof in the living room ext and I have decided to re-plasterboard the whole area about 10ft x 8ft. I will put the board up then get the plasterer who lives near by to skim it.

I am a little concerned that there is virtually no air gap between the insulalion and the roof decking. It was suggested that if I put foil backed up then I would get less possibility of condensation due to moisture migrating through the PB. If that is true would it be worth considering putting up moisture resistant PB?

you need to vent the flat roof by either installing a strip vent, or soffit vents. The insulation should be 25 to 50mm thinner than the roof joists to allow airflow, then you can use ordinary plasterboard

I know this is not a plastering question, but I will either have to take some of the insulation out or somehow squash the insulation to force a gap under the decking. I assume the air gap has to be above the insulation.