Insulating a flat roof ceiling

[pete s.]

Hi all, I have a bedroom with a flat roof with no insulation! I was thinking about insulating and re boarding over top of original ceiling as room height is good. Options I’m considering;
1. Add 3x2’’ battens over ceiling, infill insulation boards between battens then p/board over top?
( would I need an air gap between new p/board and insulation boards? Wld I need a damp barrier plastic sheet?
2. Just attach plaster board with insulation already attached direct to old ceiling, fixing to joists?

Any advice welcomed, thanks.

 

[motorbiking]

No battens needed, they decrease the insulation.
If you can find the beams/joists, you can simply board over with insulated plasterboard or use 50mm celotex and regular plasterboard. You can use plasterboard adhesive foam to stick it to the ceiling and screws to support. No need for damp barrier. make sure that all the gaps are sealed with foam and that you leave the correct spacing for any downlights if fitted.

So option 2 or use celotex and plasterboard - which is cheaper.

 

[pete s.]

Thanks for advice, appreciated!