Insulation dormer roof void

[andyp187]

I have a 1960s chalet style house with dormers. Behind the front wall of the dormer is a vented space which makes the room very cold. I have accessed the void by cutting through the wall. It’s pretty tight and I’d like to insulate the walls of the room from behind the plasterboard. Could spray insulation be an option here? Can’t see it being an issue but there are lots of horror stories. Wriggling through with celotex doesn’t appeal!

 

[freddiemercurystwin]

I expect you would find it cost prohibitive, I believe the kits are quite expensive. as for the floor, 300mm of rockwool will be fine and easy to do.

 

[DAZB]

Either PIR boards or the rigid cavity wall batts are the best option in my opinion. Not easy to do but you will be glad you did.

 

[andyp187]

Thanks, I’ve bought one can of spray foam to see how it goes, the access is really right. If it sucks I’ll revert to PIR. Might try to slot some cavity wall batts in above the void to insulate the wall above as after investigating that seems to be insulated with spider webs only

 

[Mike13]

One can will not go far, barely even one segment of the wall. Work out the number of litres it takes to fill all the space between the timbers and work out how many cans that would be before you start.
eg 10 cm thick x 1 meter high x 2 metres long will be 200 litres of foam. scale for your wall

 

[hllns]

You have to also be aware of what you do with the services, if you put insulation over the ring main cabling the current carrying capacity may be reduced as it can't dissipate heat as well.