A. You need to only use an set up technique that the insulation contractor is familiar with. Right here during the Northeast, lots of contractors would possibly fill your rafter bays using the dense-pack strategy following your new roof sheathing was installed.
If you need to build an unvented insulated roof assembly, you've two alternatives: (a) You'll be able to include rigid foam to the exterior aspect of the roof sheathing, followed by a next layer of roof sheathing and new roofing, or (b) You could insulate the underside of the roof sheathing with spray polyurethane foam.
Q. "You say 'You don't need an inside vapor barrier,' but You furthermore mght mention that 'You'll need a fantastic air barrier on both sides of one's fiberglass batts.' The latter would turn out to be an interior vapor barrier not so?"
Thanks Martin - Now I see why my unique plan for any SIPS envelope was so elegantly basic. It looks like min R-ten sprayed under the roof sheathing and afterwards an entire-fill from the bays with batt / fluffy, as well as a vapor sealed drywall lid will get me the 'very hot' (unvented) roof method the SIPS was from the get go.
Should I treat the flat roof like a cathedral ceiling and go along with spray foam (or board), fiberglass, and no moisture barrier?
The leading flaw In this particular roof appears to get the ice and h2o membrane at the very best stage in the rafter bays. Would just standard felt paper have allowed ample moisture to dissipate in the roof sheathing keeping away from rot?, I form of doubt it.
A. It is smart to you personally since it click over here now satisfies your needs. As you're mindful, it's not a great method to insulate your roof assembly. But you have described it as A brief stop-hole evaluate.
Be sure to install insulation that gives at the least the least code prerequisite for ceiling R-value. Insulation that exceeds the bare minimum code prerequisite is a lot better.
Magic bullet position is not reached. It's a structure for the minimal slope roof. It can be very much together the lines of Doug McEvers utilization of higher perm fibre board to generate vent channels higher than dense packed cellulose.
"Just about every house is unique. The aspects which will have saved the roof sheathing of the home you explain could incorporate:
We really Will not know if these roofs have right vent channels, or what sort of vent baffles (if any) ended up applied to maintain the ventilation hole among the best of the fiberglass insulation and also the underside with the roof sheathing.
Your decide to use two-inch-thick EPS as your ventilation baffle will get the job done. The EPS is fairly vapor-permeable, so it will allow a little bit of outward drying. (In any circumstance, should you Create a reasonably airtight ceiling, there visit their website will click site not be any moisture In this particular assembly that should escape.)
As I stated within the write-up on this webpage, you can't use fluffy (air-permeable) insulation within an unvented roof assembly Except you incorporate rigid foam or spray foam earlier mentioned the fluffy insulation.
However, I believe you're Improper regarding your asphalt felt; I doubt When the felt is impermeable to drinking water vapor. Most sorts of asphalt felt are somewhat permeable -- generally five perms when dry and approximately sixty perms when wet.