insulating garage

[lister]

I have a seperate garage with a pitched roof which I use as a home gym. In the summer this gets unbearably hot so this year I was looking to try and insulate it against heat somewhat.

I was wondering what would be best for this? I was thinking of perhaps slotting sheets of expanded polystyrene between the roof rafters. Would this be effective? Would it cause any problems with damp etc if I butt it right up against the black sheeting stuff that is behind the tiles? Any other suggestions?

Many thanks

[dom]

2 reasons not to use polystyrene - it's inflammable and produces toxic gases when it burns - and it is a problem if it comes into contact with pvc covered wiring as it leaches the plasticiser and can cause the insulation to crumble.

More appropriate materials would be rockwool or kingspan.

[Stuart Noble]

The idea is to leave a 50mm gap between insulation and roofing felt, (unless it's the newer breathable type). This usually leaves you with room for 50mm of something. Celotex is best but the dearest. Check out the properties of polystyrene. I don't think its fire resistance is that bad

[dom]

Agree with your other points, but unless it's fire retarded polystyrene it doesn't look good:

[visionset]

It's a friggin detatched garage, I don't expect he's going to sleep in it! Or do you suppose being 'in the zone' will make him oblivious to the fact his garage is burning down?

[manatbandq]

And arrange for adequate airflow through the gap.

MBQ