Q. "You say 'You don't want an inside vapor barrier,' but You furthermore may claim that 'You'll need a good air barrier on both sides of the fiberglass batts.' The latter would transform an interior vapor barrier not so?"
We'll give it a check out. Present is a fourteen yr aged roof with 2" of closed mobile roofing foam with the acrylic elastomeric coating.
"The normal roof air flow requirement Utilized in constructing codes and asphalt roofing companies calls for 1 sq. foot of "Internet free ventilation spot" for every 300 sq. toes of ceiling region (attic ground space) when vents are evenly divided — half of them significant within the roof with the ridge, gable, or a superior roof, and half reduced within the roof with the eaves.
According to segment R806.3 of your 2006 Global Residential Code (IRC), “At least a 1-inch House shall be supplied in between the insulation along with the roof sheathing and at the location with the vent.†Such a vent Place may be established by setting up 1 inch by one inch “sticks†inside the upper corners of each and every rafter bay, followed by rigid cardboard, slender plywood, OSB, fiberboard sheathing, or panels of rigid foam insulation.
Q. "I've not long ago attained access to low-cost roofing polyiso -- black backing on both sides. My emotion is the fact that putting this backing against the rafters in contact with that vented air may very well be inviting a mould issue, and if i encounter it to the place i lose the radiant barrier."
I must surprise If your failure during the Photograph might have occured In case the hip and ridge was vented and everything else the identical?
Martin, I am grateful for your time and effort, and after looking through numerous of the replies, I'm able to see you happen to be keen about creating matters ideal. Appropriate for people today, and also the planet. Thank you for Anything you do!! Ryan Nelson
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Your proposed assembly is actually a code violation. If you need an unvented roof assembly, you should hold the roof sheathing warm with spray foam or rigid foam. Cellulose insulation is classed being an air-permeable insulation and cannot be Employed in this kind of roof assembly.
However, I feel you're Erroneous about your asphalt felt; I doubt When the felt is impermeable to drinking water vapor. Most varieties of asphalt felt are rather permeable -- ordinarily 5 perms when dry and nearly sixty perms when moist.
Just like all types of vent baffles, it’s a smart idea to pay attention to airtight construction approaches, especially if you're going to be setting up air-permeable insulation in the rafter bays. Seal the sides of every panel with caulk, and tape the seams among panels that has a significant-high-quality tape. (Should you be setting up air-permeable insulation like fiberglass, mineral wool, or cellulose, the ventilation baffle isn’t optional; it’s necessary.
Also, wouldn't the site-crafted plywood baffles among the rafters have the similar problem; slow drying by way of diffusion? ( I suppose I could use fiberboard for baffles)
Thank you for the suggestions, Martin. Inexperienced Developing Advisor continues to be the best for answering certain questions I've experienced within the basement all of the way to the roof. I would not be capable this content to build my own dwelling solo similar to this without you and other audience serving to me out with facts.
I am not a fan of complete peel-and-adhere roofs, for various good reasons. But your that site program will most likely be wonderful. Just Be certain that your roof sheathing is dry about the day you install spray polyurethane foam -- because the sheathing won't be drying greatly in possibly path just after It really is encapsulated concerning peel-and-adhere membrane and spray foam.