Attic and roof stack
Does this seem like it will work? Austin TX, Climate Zone 2A.
From inside to outside. Air barrier at the interior ceilings.
Drywall (or lath and plaster ceilings)
Blown-in Cellulose (~16 inches, but less over outside walls, as no raised heels)
Mostly solid wood board sheathing (from 1950s), one area of low slope plywood (~1.5 in 12).
Solitex Mento as roof WRB (or other vapor open WRB)
Counter-battens (1x material criss crossed)
The attic is vented through gable vents but there are no ridge vents (there are two solar power fans but I would remove them). I do not have vent channels under the sheathing and our attic makes it very awkward to install them (lots of over-roofing with multiple extensions). My concern is that the blown-in insulation will contact the sheathing in the eaves (possibly 2 feet in as well, depending on how deep we get it). So the intention is to give really good drying potential above the sheathing. From what I’ve read this should work fine for the solid wood boards, possibly less so for the low slope plywood? We’d strip the current asphalt tiles and tar paper on the roof.
We considered insulating at the roofline (foam or rockwool comfortboard) but it’s rarely done here, the gable to wall details were complicated, and the cost very high. So I’m hoping to have a roofing contractor do the WRB, battens, and metal roofing install and handle the insulation myself.
Another possibility is Solitex UM (with integrated vent mesh) rather than the counter-battens?
So the main question here is: if blown-in cellulose is against the underside of the sheathing can venting above the sheathing make things reasonable? Or is the fact that warm, humid air inevitable leaking up from the house condenses on the underside of the cold sheathing in winter, wetting the cellulose, just too problematic?
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