Bedroom floor/garage ceiling insulation

[Wato]

Hi all,
I need to insulate the floor of my bedroom which is above my garage, the garage ceiling is plaster boarded and skimmed. I was considering fixing battens/joist 90Degrees to floor joist then insulating with 75mm Celotex then fixing new plaster boards then re-skimming.
My only concern is the void between ceiling and floor, am I defeating the object and leaving a cold void, should I pull the existing ceiling down and insulate between original flooring joist. Could I have injected insulation ?. What is the correct way to go to conform with building regulations, my house is 6 years old, I have pre drilled ceiling and the builders have insulated with fibre glass but it does not seem up to much. Any help would be much appreciated.

 

[noseall]

To meet current standards you would need say 150mm glass-wool insulation in void, plus 50mm celotex across joist bottom

 

[Wato]

Thanks for your advise, please could you also confirm if I fix celotex to underside of existing ceiling would this conform to building regulations or should I fix new joist at 90Deg to existing over plasterboard fit celotex and reboard and skim for fire protection ?

Regards

Wato

 

[noseall]

You will definitely require skimmed plasterboard (usually fireline board) as the final covering, if it is a garage under the bedroom.

 

[Wato]

Thanks, I now know what I am doing a bit later in the year.