bedroom above intergal garage. Insulation?

[jiobloggs]

Our master bedroom is directly above our intergal garage. The house is having bead cavity wall insulation installed in 50mm cavity ie in garage front and side walls. Back wall is single skin masonry adjoining a living room and other side is empty 50mm cavity double skin wall adjoining the kitchen. The garage door has 25mm expanded polystyrene fixed to it.

Is it worth insulating garage ceiling (foam backed plasterboard attached to existing ceiling)? or back and side walls? Nothing between ceiling and carpeted bedroom floor at present.

 

[noseall]

You treat the garage as external space and insulate accordingly, in a similar way you would insulate your loft.
Because we can't usually get sufficient thickness of quit insulation into the floor space and to prevent cold bridging, it is recommended that a combination of celotex and quilt is used.
Use say 50mm celotex across the joists wth plasterboard plus 150mm - 200mm of quilt between the joists.
This will satisfy latest standards.

The 25mm polystyrene fitted to the garage door isn't worth squat in terms of overall thermal resistance.

 

[^woody^]

You need to insulate the room, not the garage. So insulation should be in the floor.

Another reason is that if the joists are built into the wall, air leakage will be cooling the floor void making insulation on the garage ceiling useless.

 

[noseall]

You need to insulate the room, not the garage. So insulation should be in the floor.

Another reason is that if the joists are built into the wall, air leakage will be cooling the floor void making insulation on the garage ceiling useless.

I admit that I have only ever seen designs where both are used and corroborated by BC.

Surely if there is a complete sheet of insulation across the ceiling then this must mitigate some of the cooling within the floor void? Would your argument still stand if the garage wall cavity was insulated?

Would it make more sense to have the celotex fitted to the underside of the floor boards? If so, why have I not seen it designed this way regards garages? Thinking about suspended timber floors, it does make more sense.

 

[^woody^]

Would it make more sense to have the celotex fitted to the underside of the floor boards?

Yes that's it.

Many people lose sight of what the insulation is there to do. It is the room that needs to be insulated from heat escaping, not the garage insulated from cold escaping.

It's no good having heat escape a room into a cold draughty floor void, which is then insulated.

Similar concept to A Searle's vapour barrier argument, with the barrier (insulation) being placed as near to the room as possible.