Cellulose Insulation for a Cathedral Ceiling
Hi there! I’ve read a couple of articles and discussions on this site related to insulating cathedral ceilings and installing cellulose insulation. I still have a couple of questions.
My partner and I have a 70s-built A-frame with cathedral ceilings. The walls currently have no insulation (it was previously used as a summer house), so the roof sheathing is visible from the inside (see photo). We were initially going to get spray foam, but it’s beyond our budget so now we are weighing our options for a vented system. As for climate, we live in Atlantic Canada.
Here’s what I have in mind: install a ventilation baffle (that can withstand pressure from blown cellulose) against the sheathing, then cellulose, then rigid foam board (to create a barrier between the rafters and the interior wall), then a vapor barrier, then drywall over top. The depth of the rafters means that there’s only enough room to do about 4.5″ of cellulose over the baffle, plus the rigid foam board. The baffles would vent into an attic space at the peak of the building, which would also have cellulose blown on the floor.
– First off, is there anything problematic about this assembly?
– Is having a vapor barrier only on the interior side enough, or does it need to enclose all of the cellulose? I ask because, in Martin’s cathedral ceiling article, he states “If you are installing air-permeable insulation like fiberglass, mineral wool, or cellulose, the ventilation baffle isn’t optional; it’s required. Air-permeable insulation materials need to be enclosed by an air barrier on all six sides.”
– Should the baffles be sealed off as much as possible to prevent air from traveling from the cellulose to the ventilation cavity?
– Would dense-packed cellulose (3.5 lbs/cuft) be the preferred installation method over loose-fill for this type of vented assembly?
– Is dense-packed cellulose possible to DIY with a rented machine? If so, what’s the best way to achieve the proper density?
– Would anyone recommend a different type of insulation over cellulose for this set-up, such as rockwool?
Thanks in advance!
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