Flat roof cathedral ceiling we re going to give it a try.
Vaulted roof insulation detail.
Our plan is to put rigid board up between the 2x4 s caulk the edges and then hang sheetrock.
In the knee wall area the insulation is in the floor and on the back of the knee wall.
Existing is a fourteen year old roof with 2 of closed cell roofing foam with an acrylic elastomeric coating.
Vaulted ceilings can be constructed by either stick framing which means attaching each joist and rafter individually or by setting roof trusses that come engineered from a truss manufacturer with.
As it expands the foam seeks out the gaps cracks and crevices and fills them in.
There are several options for installing insulation in a vaulted ceiling.
Nail 1 furring along every rafter side against the roof deck.
Cut and insert 1 or thicker high r foam insulation sheets r 8 per inch against the furring giving a 1 or greater air path between the insulation and the roof deck under the cathedral ceiling.
Below is 1x decking and 2x4 rafters.
The insulation is not affected by water.
Among the easiest options is to install rigid insulation sheets over the rafters which not only provides insulation but also the structural function of enclosing the roof.