I'm vaulting the ceiling in our top floor. The roof has several trusses then purlins supporting the rafters.
I'm putting 240mm of pir against the underside of the rafters. The insulation depth takes it beyond the bottom of the purlins.
For the plaster board, and because the purlins are so wonky bonky, I was planning on battening at 90 degrees to the purlins, placing them across the top of the pir boards and then fixing them to the purlins, packing out each one as required.
This will leave an air gap between the plaster board and the por board. Is this an issue for condensation, or as the pir board is the 'warm' side will it not matter?
Thanks for any advice