Internal Insulation

Hi,

just looking for some advice,

I’m renovating the house, it’s a 70s house.

Currently installing underfloor heating in the upstairs bedroom, have removed the entire floor, battened out the joists and installed 50mm solid foam insulation with under floor heating pipes on top.

have foam sealed around the joists where they are set into the wall, and added more 50mm insulation vertically between them.

So the under floor itself has been relatively well insulated, on top I’m installing 22mm chip board flooring which will be glued between the joints and foam sealed around the edges.

so now I’m focusing on the walls.

House has a 50mm cavity filled with the fluffy mineral wool insulation on 1 exterior wall.

so what I wanted to do was build an internal stud wall, install 50mm rock wool between the studs, then vapour barrier over the top and plasterboard.

on the adjoining other exterior wall, there is no cavity... on the exterior there is a felt membrane and tiles as cladding, then there are basically just hollow concrete blocks and plastered on the inside.

on the inside, want to build a stud wall with 100mm rock wool insulation and again vapour barrier and plasterboard.

so 100mm insulation total on the external walls with vapour barrier and plasterboard...then continue this vapour barrier across the ceiling before over boarding with a 2nd layer of plasterboard. All to try and increase the air tightness a bit and insulate the room better even if it reduces the size slightly to try and maximise the benefit of underfloor heating and keep the heating source temperature as low as possible.

once I’ve done this room I will continue the same theme throughout the other upstairs bedrooms and exterior walls downstairs as well.

but I just wanted to know if there was any special considerations I needed to take into consideration?

thanks

People who've done it seem to glue celotex to the walls and plasterboard over, easier, takes up less space and avoids the cold bridging you'd get with timber studwork.
I think someone on the forums has done it and got the teeshirt - Jonbey?

Yeah, everbuild pink dry fix foam, stick boards to wall with it, stick plasterboard to them. A few mechanical fixings if you don't trust the glue to last forever or worry about them falling off the wall in an inferno. You could replace the 50mm studs with 25mm kingspan for similar results.

yes, the depth of the non cavity external wall. If it's less than about 220 mm then they strongly advise (and building reg's would insist) that you leave an air gap between the wall and the celotex (or any other PIR insulation). We left 25 mm because the brickwork is so uneven, but the BCO would have been happy with 15 mm. I don't know exactly, but would have thought 50 mm of celotex would be equivalent to 100 mm rockwool. You can get plasterboard insulated with PIR which you could fix over the top of 3 x1 treated timber battens at 400mm centres. Strip of DPC on the back of the battens.