Loft conversion - thin insulation - what are my options

[mushymat]

Hello everyone!

Can anyone tell me a reason not to use roll insulation (the same as the stuff you get in campervans), or underfloor insulation as an additional layer of insulation in the ceiling of a loft conversion ?- it would then be covered in plasterboard

long story shot - we have a section of celing that I cannot add 25mm pir (like the rest of the room) because we have a custom door (that fits within the pitched roof) that the additional 25mm of PIR would block its opening and closing, and I dont have the time (or the understanding wife) to rebuild a door frame/cut the door down. So im looking for an option of around 10mm or so

I did wonder if a layer of underfloor heating mats (+ vapour barrier) might be a workable option?

Any thoughts would be great

 

[freddiemercurystwin]

Because to use the proper building grade types of foil insulations which, for them to work as intended they require an air cavity each side which by the time you add up the overall space required and additional battens to create the gaps it negates any potential space or cost savings over traditional PIR insulation.

 

[endecotp]

You can get XPS insulation thinner than 25mm. It’s fractionally better than nothing. (Or aerogel - though warming the room by burning banknotes is probably cheaper.)

 

[foxhole]

Why only 25mm Pir . Loft would need 100mm. Are you diying?
Are building control involved?