Set up a layer of closed-mobile spray foam towards the underside on the roof sheathing, and fill the remainder of the rafter cavity with the air-permeable insulation. Once again, such a assembly is designed to dry to the inside, so the assembly need to in no way consist of an inside polyethylene vapor barrier.
The primary flaw During this roof appears to be to get the ice and water membrane at the very best level from the rafter bays. Would just normal felt paper have permitted adequate humidity to dissipate from the roof sheathing avoiding rot?, I sort of question it.
Next, could you make sure you affirm this: "If you'd like to use just one variety of insulation in unvented rafter bays, that you are restricted to spray polyurethane foam."
In order to use rigid foam, the best destination to set it really is on top of your roof sheathing, not beneath your roof sheathing.
A. The air barrier could be a vapor barrier, since the rigid foam is usually very likely to be described as a vapor barrier (or near it) in any case.
From the absence of the airtight ceiling, roof ventilation can perform a lot more damage than great, since air motion in rafter bays can stimulate indoor air to leak through ceiling cracks.
A. Possibly approach will work, provided that you get at the least the least code R-price for your roof, and as long as you use building approaches that listen to airtightness.
Many thanks - This really is new building, I am the designer / builder, and the more I examine it, I am liking all rigid - fewer fussy. The top layer of rigid more than fluffy can make my eave way too thick anyways. The air barrier to the T&G ceiling is in fact the sandwich of felt and taped 3/eight" CDX.
Alright, I was figuring that the entire with click to investigate the rigid foam + cellulose had to be a particular R-price together and were thinking about working with much less rigid foam. I've been reading through about distinct types of cellulose. Considering that I am setting up from earlier mentioned would some thing like stabilized cellulose get the job done as it has somewhat drinking water additional?
Why not simply do it ideal additionally Construct with force taken care of roof sheathing. Even normal plywood can manage wetting cycles repeatedly in excess of our number one super reasonably priced OSB.
I think here are the findings that Invoice Rose is correct: all these failures entail moisture that's carried by going air. These are generally not diffusion failures. If the rafter bays genuinely are appropriately dense-packed -- a big if -- the prospect of air movement may be very small.
. Unvented roof assemblies are Risk-free. The primary reason that some individuals install air flow channels earlier mentioned the rigid foam is since they are in places with a great deal of snowfall, and they prefer a "cold roof" to attenuate ice damming problems. Thanks for your comment. I will edit my posting to try to make clear any ambiguity on this difficulty. .
I purchased a disaster of Check This Out the household which was partly remodeled, It really is in Zone sixteen (a California designation just like IRC zones). It's a six/twelve vaulted ceiling in excess of the living/kitchen area area. The roof is held up by two very long beams that run 4 toes out parallel on the ridge , Consequently there's no straight air route a the way as much as the peak ridge beam.
Recall: if you select to install rigid foam along with your roof sheathing, don’t install ventilation channels underneath the roof sheathing; both of these tactics are incompatible.