Standard PB v foild backed v moisture resistant Ask your questions and find answers on many subjects relating to plastering and dry lining

[Kevin1996]

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?

[welsh brickie]

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

[Kevin1996]

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.