Hi, I am looking for some advice on insulating my loft. I want to put PIR boards to cover the rafters. The rafters are only 73mm deep so in order to provide the regulation 50mm air gap it seems best to just fix the boards straight to them rather than try and infill.
I assume screws are the best way to fix them to the rafters, If I am using 100mm thick board how long do the screws need to be for best purchase? I had assumed 110mm screws would be OK.
There are quite a few longitudinal binders in the way, I assume it is OK to just cover them in the board as they aren’t too thick. I don’t imagine its safe to remove them, unless the boards would replace that stability?
The house is a terrace with exposed breeze block at the gable ends. Would I also need to clad this? If so can I fix straight to the wall or does this need an air gap too?
Finally the floor has fibre insulation between the joists which extends to the roof membrane. If I then place board over the rafters would this mean that in fact there is no air circulating? Not sure if this closes the air gap I am making for the boards.
