I have a plain wall (no reveals) with 24mm deep p/t battens, between which will go 20mm celotex, then 20mm celotex & 9.5mm PB on top. That is the limit after removing architraves.
Do I have to maintain battens at 450mm centres when the insulation braces the PB?
Just happened to notice quite a few walls on the internet have obviously >600mm spacing with 12.5mm PB, relying on it seems the insulation to stop the PB flapping around & joints cracking.
There is a "new" specific foam for this - "insta foam". It is low expansion but high strength and very fast, but is gun only and tends to trash guns quite quickly.
A few hammerfix re obvious fire regs. With expanding foam you would need them quite quick :-)
I always skim, simply because wallpaper when stripped off plasterboard can be a right mess :-)
I will foil tape the joints, it is 2 layers of 20mm celotex so there will be quite a good vapour barrier. It is a box-room so limited moisture issues.
It just looked like a shed load of wood piled ready for the wall !! However the second layer of celotex will minimises the cold bridging of wood and 40mm PIR is a whole lot better than nothing in a "2 outside wall & prevailing wind" room.
With hindsight I would "bollocks to the spirit of BR" and use 40mm rough-cut eXtruded PolyStyrene, bond it to the wall, a few stainless "giant drawing pins" re fire, and directly skim the suface.
I only recently saw them.
It came down to what I could get cheaply as seconds for my mother. It gives her a "super-insulated bedroom" if the heating were to say fail or other work needs doing on her main bedroom.
PIR foam is quite a price, but seconds can be really cheap (=A34 per
20mm sheet, only light edge damage).HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.