If you would like put in a mix of closed-mobile spray-foam about the underside of the roof sheathing and air-permeable insulation in between your rafters — an solution often named “flash and batt†— the setting up code requires that spray foam (or, arguably, rigid foam insulation) be “used in immediate contact with the underside from the structural roof sheathing†and which the foam insulation satisfy the necessities “laid out in Desk R806.
You don't want to utilize insect display, for the reason that fiberglass batts have to be enclosed by an air barrier on both sides. If the prime aspect of fiberglass batts are matter to wind-washing, the shifting air degrades the performance with the insulation.
We had a Zip Roof set up and a metallic Roof positioned over it. The roof assembly will not be vented and taped all round the soffits. Preferably I might want to pack the complete cavity with blown cellulose. This string of conversations is offering me pause for imagined.
Here's the typical respond to for those who really need to adjust to most setting up codes (The solution emanates from an report by Mike Guertin):
Code would not seem to be to use as it's grandfathered in. It looks like I ought to redo the corridor ceiling.
I'm somewhat stumped on this one particular - I'd want to vent this roof assembly, but I can't say no matter whether there'll be a all-natural convective stream as there would be with rafters sloping With all the roof pitch. My rafters are running stage Nonetheless they sit on parallel curved prime plates. I'm able to use twelve" rafters and make 10" of batt get the job done, leaving a lot of air flow space. I'm able to drill the tops of the engineered joist flanges to permit ventilation 'up-slope' (perpendicular into the rafters) together with inside the rafter bays, and I can offer ongoing perimeter ventilation (Cor-A-Vent strip) at my roof fascias (eave, ridge and gables).
Most commercial roof assemblies Will not hassle Using the fluffy things. They simply fulfill one hundred% of your R-value requirements for your roof with rigid foam (either EPS or polyiso) and skip the batts fully. That's the way I recommend that you choose to progress.
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It is high-quality so as to add foam board previously mentioned the roof deck Despite having the shut mobile foam-board (what type?) on the interior. Roof decks can't dry to the outside Discover More by 0.1 for every shingles anyway, especially because in zone five it will spend an important amount of time protected in snow/dew/rain with the moisture drive heading inward, Clicking Here not outward.
Ideally, you ought to have an airtight barrier higher than and under your fiberglass batts. If you're able to realize All those two air boundaries, then wind-washing is just not an issue within a roof like yours. (It can be in a very vented unconditioned attic, certainly, Particularly close to the soffits.)
Many thanks for the confirmation and suggestions. Considering that all the things is dry this time of 12 months and the home was lately tented for termites, I'll insulate through the beam and seal up the apparent air entryways. As soon as I'm able to see within I feel I'll have an improved concept how much dampness is in there through the years.
If you wish to use only one variety of insulation in unvented rafter bays, you will be limited to spray polyurethane foam. Another probability, not surprisingly, is to create your roof with structural insulated panels (SIPs).
The GBA Web page won't present custom made particulars. That is what an architect or an engineer is for; I advise that you employ one.
Many thanks Bonuses in your response Martin. Would you still be happy to employ that unvented strategy to get a renovation problem wherever There exists non-breathable membrane (eg bitumous 'felt') previously mentioned solid board sheathing?