Your assembly requires about 5 inches of XPS, for a total R-price of only R-25. That is not much. In the event you are likely to all of that issues to develop an advanced roof assembly, you'll want to goal higher.
What obtained me started out to the "air restricted partitions and roof sheathing" was your short article of precisely the same identify; specifically South Mountain Company's wonderful article on the Martha's Vineyard housing enhancement. I noticed Marc's presentation on These houses at BBD in addition.
Most of my neighbors here have cathedral ceilings, no attics and Totally no insulation (basically they've aluzinc roofs on plywood with pine rafters).
Can it be all right to add peel-and-adhere membrane to pick out areas of the roof and retain the rest breathable with tar paper?
If this have been my house, and if the fiberglass batts are visible, I'd pull all of the insulation out of a few rafter bays to check out what is up there.
I do not determine what you suggest by "unveiled." In zone 3, you will need at least R-thirty of insulation (which suggests 6 inches of XPS). Once you've installed R-thirty of spray foam or XPS, you might be accomplished. You can leave an air Room among The underside of the foam plus the drywall If you need.
The aged Canadian guideline -- at the least two/3 of the entire R-worth on the exterior aspect of the vapor barrier -- is really a tough-and-All set way to address this query; it's also possible to solution the dilemma by undertaking a dew-level Assessment or maybe a WUFI Evaluation.
November 18, 2011 Picture one of three A leaky ceiling doomed the roof sheathing. The ceiling of the ten-year-aged property was Minimize for an electrical box, and also the outsized hole was hardly ever caulked. Humidity-laden air entered the rafter bays through these cracks. Once the humidity encountered chilly roof sheathing, it condensed, bringing about humidity accumulation and rot. (The rubberized membrane while in the Image was applied as a temporary patch to get a hole while in the roof, and did not add on the failure system.) Image Credit score: Peter Yost A leaky ceiling doomed the roof sheathing. The ceiling of this ten-year-outdated property was Reduce for an electrical box, and also the outsized hole was never caulked. Dampness-laden air my response entered the rafter bays by these cracks.
"When you have set up the code-mandated thickness of rigid foam over your roof sheathing, you’re totally free to setup as much fluffy stuff as you would like in between the rafters."
and not less than at the ridge, wherever joints are close alongside one another, to can foam with lower expansion flex foam Issues I have are
I need to marvel If your failure from the Image might have occured When the hip and ridge was vented and anything else a similar?
Will it seem sensible to spray and Minimize and cobble four inch closed cell foam/board on underside company website of sheathing accompanied by fiberglass In the bays and 1 inch of eps/iso beneath the rafter (to stop thermal bridging) right before finishing with drywall? Will I create a vapor sandwich and far better go away the ultimate EPS and acknowledge the thermal bridging?
So a hybrid method has to be investigated. Dense packed cathedrals with warmside ridged foam so as to add R, taped, no recessed lights or other air paths after which belt and suspenders... Include venting Regardless that there is no usual 1" vent path.
Q. "Are you saying that increasing ventilation to that second Tale attic would in fact be a foul thought, if we proceed the foam in excess of your entire second Tale gable roof, and as a substitute we must always ensure it is absolutely unvented?"