A-Frame cathedral ceiling roof insulation
JohnDownie
| Posted in Energy Efficiency and Durability on
I have a question: In the case of an A-Frame new construction house, Zone 5A, we’re planning to have glulam structure (60 degree slope) at 4-5′ O.C. with 2×6 T&G sheathing visible from inside spanning from A to A. That means that all of the insulation would be outside the sheathing, Current code calls for R-49. I expect we will have unvented rigid insulation layer on top of the board sheathing. I’m thinking that we’ll need 7.5″ of rigid insulation to get that R-49. Will I need another layer of plywood sheathing on top of the rigid insulation to attach the underlayment and metal roofing?
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Replies
Assuming you are calling for ISO and assuming you've used a design standard of r6.5/ inch. That's a generous allowance.
Possible to frame a non-structural vented assembly over the bearing assembly. Many ways to skin the cat.
You'd quickly regret attempting to install metal directly to deep foam. My preference, with deep exterior foam and metal roofing, is another deck. In some instances, a manufacturer will require decking versus strapping. The exact tactic here is something to discuss with your builder and confirm with your roofing manufacturer. And again, see comment regarding vented assembly.