PeterR

Thank you very much guys, it’s a big big help ?

That’s the problem, the thickness of the joists is only around 50 mm so I can only fit 25 mm PIR board, which is far from the recommended 100mm. Is there any solution for this?

That’s what I want to do. Rip out old plasterboard, stick PIR between studs,seal it with expanding foam and then put new insulated plasterboard on top of that. I just wasn’t sure if I can fully fill the gap between plasterboard and sarking felt or I have to leave some gap for the air flow.

Thank you Tony for your help ?

Hi Dave, thank you for your reply. Do I need airgap in the wall as well, where the hole is on the picture and also around the window? Or can I fully fill the gap with digit foam boards and stick plasterboard on top? Thank you

Hi, I’ve got a chalet style house built in 1960s. The upstairs bedrooms are really cold in the winter and I’ve opened up one of the walls to see what’s behind it and found out that there is no insulation whatsoever. Behind the plasterboard there is a gap and the the rafters/studs are only 5-7cm deep. There is some old darling felt and then plastic cladding. The question is how to insulate the walls and the sloping roof from the inside? Because the gap is quite small I can’t fit the 100mm insulation boards between the studs/joists and also don’t want to loose over 10cm of floor space in the rooms as they are quite small. Do I need to leave an air gap behind the insulation in the walls? Also, can I stick insulation board on top of the existing plasterboard and will I need a VCL between any of the layers? Thank you