Vaulted ceiling, open attic
I have two vaulted ceilings that I am trying to work out how to insulate. I have read all the material here on insulating cathedrals. However these are essentially a variant on an unconditioned, vented flat attic. If the roof is 6/12, the ceiling is 3/12. Unfortunately while they are not a classic cathedral with only a stud’s depth, they still have very little space between the ceiling joist and rafter, ruling out fluffy insulation. (The R-38 batts already brush the roof sheathing halfway down the slope) Dense pack, of course, I hear is a very bad idea due to moisture.
Access is also extremely poor, while the space is open & connected to the regular flat attic, only a small child can enter. You’d really either need to go through the sheathing or drywall, like with a cathedral.
So we are left with rigid foam, I believe.
If I apply continuous rigid foam outside the sheathing, I need to seal off the vaults from the flat attic and remove the venting.
If I cut and cobble between the rafters, I would want to make 1″ vent channels above the right and still seal off the vault from the flat attic.
But in either of these cases I have appreciable dead air between the Batts and the rigid foam for convection. Is this an issue?
Are these all of my options? Is one clearly superior? Are there options that do not require sealing the vault from the flat? Lastly, can anyone tell me what this type of ceiling attic combo is properly called? 🙂
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