Unvented loose-fill cathedral roof in Zone 9
Not to beat a dead horse anymore than we need to (!), but I’m embarking on a foam-free build in zone 9, with a cathedral ceiling that will be insulated with a loose fill batts of sheeps wool.
I’ve gotten lost in the debate about loose fill unvented chathedral roofs, although I understand that is isn’t advisable, and very clear attention to detail is required. The hiccup is that the house is clad to weather, and the roof is continuous down the sides of the walls (no eaves) and there is a only a 3/4″ air vent between sheathing and cladding, vented out the ridge cap on the roof from the bottom of the wall. It’s completely finished on the outside, so whatever safety nets I can do can only happen from the inside.
My question is, what can I do to set myself up for success? internal air gap between sheathing and insulation, that goes nowhere? or an internal air gap continues down to the bottom of the wall? or is a 3/4″ gap enough and with excellent vapor barrier detailing it will likely be fine.
Here is the roof structure, from the outside in:
1) Steel roofing tiles
2) 3/4″ air gap (furred with 1×4)
3) #15 felt
4) 1×6 planking on a diagonal
6) Vacuum insulated Panels (VIPS) between trusses
7) loose fill with sheeps wool batts
9) 2×4 service cavity (for electrical etc)
10) 1×6 pine boards
Thanks for your feedback in advance!
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