Polyiso is used on a regular basis for this kind of roof assembly. Polyiso isn't going to outgas. It is a lot more environmentally friendly than XPS -- and it's the next R-price per inch.
Hence the problem is: seal the stucco vents and insert the spray foam roof and Don't be concerned about condensation? There may be little or no minimal-hanging fruit inside our style of building, Specifically on existing houses, which is why persons are getting sucked to the spray foam roof scam.
The most beneficial solution is to complete all the operate simultaneously: rigid foam higher than the roof sheathing (as advised while in the article), and fluffy insulation underneath.
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Doug I concur, a lot of wrongs "overthinking" and overdoing. I as soon as needed to resupply a doctor developing an plane with dozens of AN aircraft bolts simply because they were tightened to the point of breaking the bolts. Significantly less is much more at times... Combined with the KISS rule.
As building scientist Bill Rose has shown, code specifications for roof venting have been in no way dependant on analysis or scientific rules. In the perfectly documented JLC
You wrote, "the rafters are still exposed," but I am undecided Anything you indicate by that. Do you useful source may have kraft-faced batts among the rafters, While using the kraft facing continue to visible?
Many thanks to the input. I see a take a look at which has a structural engineer and 35 sq. of polyiso in my around foreseeable future.
As I famous previously, researcher Bill Rose has exposed the unscientific mother nature of code demands and formulation for calculating roof ventilation openings. Unscientific or not, these code prerequisites must be followed.
As your home flexes with modifications of temperature it's attainable, even very likely that some of the foamed-in air sealing will leak. It would be truly worth undertaking two" of open up cell foam on the inside side of which would be a far more adaptable and responsible lasting air seal.
I want to advertise cost-efficient effectiveness in my industry, although not for the expenditure of roof failure. We've been a 5B local weather zone with 6000 HDD, heating from mid-October to mid-April. We can also be extremely dry at 7000 ft higher than sea stage.
Lastly (I assure this is my past topic). Relating to my fiberglass batts: Will the facing that includes it retard the drying out method that I described over (will it make any difference what side I set it on in the purlin cavity?
If you put in 2x4s (or 2x3s on edge, installed with extensive screws) perpendicular towards the rafters, you will deal with many of the thermal bridging issue with no need to incorporate a layer of rigid foam.
an air barrier. If you want to install EnGard insulation batts within an unvented cathedral ceiling, you'll need to obtain a major layer of rigid foam insulation above the roof sheathing.