Insulating under ceiling?

[marcruse]

In a 40 year old house with integrated garage, and with minimal insulation between garage ceiling and floor boards in rooms above (tiled bathroom & bedroom used as an office). It's not practical to get to space from above, so I am thinking of fixing celotex board (or similar) to the underside of the currently plastered (but not painted) garage ceiling. So questions are:
1) what adhesive can I use to fix board to ceiling?
2) what thickness board should I use?
3) will it work?! ie. will the rooms above be any warmer?
Any suggestions gratefully received.
Thanks.

 

[AronSearle]

You need to check the floorzone is not ventilated or it won't achieve anything (I would not have thought it was, but check). Otherwise yes it will work.

Thicker the better, no right answer, depends on your budget really.

Don't know about adhesives as I would mechanically fix up into the underside of the joists (or at least put in a few fixings to hold it whilst the adhesive cures).

Celotex or insulation backed plasterboard?

Celotex on its own won't need much fixing, remember to tape the joints.