I have an old 1930's house, the upstairs of which is in the pitched roof space.
I've just checked and it has no insulation what-so-ever up there, so it is very much the same temperature as a loft at the moment - The layout is like so:
(Apologies for the bad drawing - only have MS Paint here!)
So the red areas have some rockwall insulation, which will be easy to top up as there's good access to the eaves. However there's no loft hatch into the top "triangle" of the roof.
The green areas have no insulation at all, so we would like to add some. We've had a quote for a company to remove all the roof tiles and battens, put insulation in between the rafters, put new felt on (there's no felt either at the moment), reinstall the battens and replace the tiles.
The rafters are only 100mm thick so we can only put 50mm of PIR type insulation between them to maintain a 50mm air gap correct? I've read that by using a breathable felt you can use a full 100mm of insulation but unsure of this?
Is there a cheaper way to do this? As re-roofing is an expensive option, but I can't see any way to get insulation effectively between the rafters on the diagonal sections.
I don't know if something like this foil double insulation would be as effective as the PIR insulation and able to be run down the diagonals if we were to install a loft hatch to get into the top triangle?
BTW, I'm based in the UK so that may alter any options.