I'm looking to build a warm-roof on a cabin, employing rigid PIR insulation and an EPDM rubber top layer.
The basic order would be, top->down:
EPDM rubber sheet
OSB top deck
PIR boards (150mm most likely)
VPL membrane (PVC sheet)
boarded bottom deck (also serves as the ceiling)
roof super-structure
So my question is whether we need to build a 'raft' on top of the bottom deck - basically a stud wall with the insulation inserted into the gaps. Or, whether we could cover the bottom deck with PIR boards to cover the whole area, and screw the top deck through the insulation into the substructure (so it's basically like an ice-cream sandwich)? Obviously we would need a frame around the perimeter for fascias and so on.
This is not a roof anyone would be walking on except when working on it and it would actually have a shallow pitch so no standing water. The sub-deck would certainly be plenty strong to walk on, but is rigid insulation OK without additional support? It seems like it probably should be with any load spread over the area and it is nicer from a thermal efficiency perspective.
Is this a)feasible b)a common approach or a little unusual?
Thanks, and sorry if I got any terms wrong I hope it's clear what I meant.
The basic order would be, top->down:
EPDM rubber sheet
OSB top deck
PIR boards (150mm most likely)
VPL membrane (PVC sheet)
boarded bottom deck (also serves as the ceiling)
roof super-structure
So my question is whether we need to build a 'raft' on top of the bottom deck - basically a stud wall with the insulation inserted into the gaps. Or, whether we could cover the bottom deck with PIR boards to cover the whole area, and screw the top deck through the insulation into the substructure (so it's basically like an ice-cream sandwich)? Obviously we would need a frame around the perimeter for fascias and so on.
This is not a roof anyone would be walking on except when working on it and it would actually have a shallow pitch so no standing water. The sub-deck would certainly be plenty strong to walk on, but is rigid insulation OK without additional support? It seems like it probably should be with any load spread over the area and it is nicer from a thermal efficiency perspective.
Is this a)feasible b)a common approach or a little unusual?
Thanks, and sorry if I got any terms wrong I hope it's clear what I meant.