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Hybrid Insulation Rockwool and Sika Rmax In Unvented Roof With 2 Vapor Barriers

leavytinyroof | Posted in General Questions on

Hi there,

I’m in Eastern Washington getting my roof finished. Feeling overwhelmed with all the different design and material options. Initially I thought of Sika Rmax cut and cobble but I’m thinking otherwise now. This is what it’s looking like so far.

Standing seam metal
Titanium PSU 30 ice and water shield
OSB
2X6 inside framing 25 degree
R23 roxul/rockwool in cavities?
2’’ solid sheets of Sika Rmax polyiso over the rafters?
Drywall over the rmax for air seal (necessary or not?)
Wood product for finish look
There’s no fans or lights in the ceiling.

I don’t mind the loss of 2” in ceiling height. Can these 2 insulations be combined in this way? Would there need to be a vent channel between the roxul and sheathing? Is it acceptable to have 2 vapor barriers: ice and water exterior/foil polyiso interior?

Is it a good idea to tape the exterior OSB seams before putting down the ice and water?

Cheers.

Hazen

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