Soldato
- Joined
- 25 Aug 2010
- Posts
- 3,030
joists are only 75mm so after leaving 50mm for ventilation could only put 25mm in.
This means it will have to be battened out regardless
you'd be as well to just do everything below the joists rather than faffing about cutting sheets to go between them, iirc once you go past 100m the fixings are a bit of a pain to get right - but everything is doable, just get the builders told!
What's the difference in uvalue? would imagine it would be pretty significant, especially in an old roof...