false ceiling in existing vaulted roof

[mellie_man]

read the sticky but have a

couple of questions to avoid condensation, putting false ceiling across top of vaulted ceiling at purlin level (existing ceiling is still lathe and plaster - no roof felt over)

1. Using foilbacked plasterboard - is it ok to fit sheet polystyrene between and over joists ( I have spare from UFH in kitchen).

2. The vertical internal wall that will now be in the 'loft', OK to line that with poly sheet too (to keep heat in from room other side and prevent condensation in that room)

3. I was planning on just making 4 off 100x100 holes (two on each side) in the existing plaster. Would this be enough for 2.5mx5m 45deg pitch space that will become the cold loft.

Any comments appreciated

 

[mellie_man]

OK sorted out points 1 and 3, anyone want to comment on point 2 whats the best way to insulate the vertical wall section in my new cold loft.

I take it just slapping poystyrene sheet on the loft (cold) side of the wall might induce condensation/moldbetween it and the wall.

anyone!?