Thorsten Chlupp is in the Substantially tougher weather and he appears to be accomplishing fantastic with straightforward free fill on the attic ground....needless to say He's using "sufficient" quantities (cellulose galore)and he has baffles close to the soffit.
I don't have many space earlier mentioned or down below the roof construction for insulation / venting. Would a flash / batt unvented assembly function underneath The only sheathing deck? My insulator has done Several of these regionally.
Do you think you're pondering the 'flat' vented cavities will never present the assembly by having an exhaust path for moisture?
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A lot of my neighbors below have cathedral ceilings, no attics and Certainly no insulation (essentially they've aluzinc roofs on plywood with pine rafters).
The air leakage that Dana described would keep the roof dry, but would undermine its thermal overall performance.
Ventilation channels are established by putting in a cloth which will sustain a separation (an air gap) concerning the insulation and the roof sheathing.
My knowing as I look at this website is usually that I would not have to worry about creating an air channel previously mentioned the sheathed portion because of the rigid foam.
I am unsure if you are interested in a making science solution or a code solution. From a code perspective, it is a roof that needs to be insulated to R-49.
I looked at the unvented schematics and I am not certain that matches the bill for up right here (Canada - west Coastline).
The R price of your Slice'n'cobbled foam + exterior foam needs to be at the least 40% of the middle-cavity R benefit for dew place Regulate for the foam/fiber boundary in zone 5. If It is coming up a bit shy of that before incorporating the outside foam it's actually not a giant offer from the short term, but when it should be 5-ten years before re-roofing to boost the foam-R to higher than 40% of the total It truly is really worth working with vapor barrier latex primer around the gypsum board, or a wise vapor retarder amongst the gypsum board & fiberglass.
You describe your proposed air barrier as "taped felt." I don't Assume asphalt felt is often properly taped, and I do not believe asphalt felt would make try this website an excellent air barrier.
I'm which includes a photo of the answer: spray foam held down with the top edge of the rafters to ensure that air might be drawn up from soffit vents to gable vents inside the truncated attic cavity.
Having said that, I do think you will be Completely wrong about your asphalt felt; I question if the felt is impermeable to h2o vapor. Most forms of asphalt felt are to some degree permeable -- commonly 5 perms when dry and around sixty perms when wet.