Garage Roof Insulations Q's

[rufus357]

Hi,

Hope someone can help me.

I have a garage that is being rebuilt as a playroom and about to insulate roof. The roof construction form top down is:

Coroline
Breathable Membrane
OSB /Sterling Board Deck
Rafters

If I insulate from the underneath between the rafters do I need to leave an air gap between the insulation and the underneath of the OSB deck? My inclinination is not as I do not want any condensation there on the OSB.

Also it seems like sapceblanket would be the easiet DIY option rather than celotex any views on this?

Thanks in advance

 

[rufus357]

OK. After some internet research - looks like I have a cold roof design so 50mm celotex with 50mm ventilation space is the way forward.

As I want the celotex level with the bottom of the rafters and fulsh against the plaster board, where does the lighting wiring run? Can it run in the cold ventilation space?

 

[catlad]

If you are going to use those materials top down coroline, osb or ply celotex, osb then joists, forget breather membrane.