DIY Doctor UK DIY Forums

Hi all,

I would like to insulate my loft's pitched roof at the rafter level using PIR boards. Most guides I have found mention insulating between and beneath the rafters, but to keep it simple, I was wondering if it would be possible to insulate *only* beneath the rafters. I can afford the loss in headspace (since I should be able to get to the required U value with just 12cm of celotex for example) and it would mean not having to deal with cutting the boards to fit between the rafters, and ensuring adequate ventilation. Attaching only one layer of boards beneath the rafters would automatically leave enough ventilation space between the insulation boards and the roof. It would also be cheaper to buy one set of 12cm boards than 2x6cm.

Are there any reasons why this might be a bad idea though? I feel like I am missing something as I don't see many guides suggest this!

Thanks!

Hi doitmyself10
Certainly you could overboard in one go but you would need to use 150mm+ screws to hold it in place and these are not cheap. You will probably need to fix on every rafter with screws at 250mm centres.
Regards S