WDR Roofing Company Austin - Roof Repair & Replacement
Austin, TX, USA
Q. "Ought to I bite the bullet and hazard of spray foam insulation, or ship the builders back up on the roof in December to chop ridge and soffit vents?"
I've already insulated the steep sides of my unvented mansard roof with 6" fiberglass (and I had it inspected), would you recommend I rip that out and use spray or board foam? I have gotten conflicting details on no matter whether to take care of it being a wall or perhaps a roof.
"R-19 batts are certainly air permeable, and on long unobstructed rafter bays you have pretty a stack impact. It doesn't have a big amount of air leakage to supply some drying there. Also, When the batts are unfaced or kraft-confronted, the drying towards the inside might be considerable.
I don't know what you imply by "unveiled." In zone three, you will need at least R-thirty of insulation (meaning six inches of XPS). Once you've mounted R-30 of spray foam or XPS, you happen to be finished. It is possible to go away an air House concerning The underside in the foam and the drywall If you would like.
If you prefer, you can Track down your air flow channels along with the roof sheathing rather than under the roof sheathing. If you decide to make this happen, make certain that any roofing underlayment that you put in above the roof sheathing is vapor-permeable — for example, #fifteen asphalt felt, VaproShield SlopeShield, or Solitex Mento — and that your local making Office accepts this approach to roof venting.
With my house the center section (20ft) is vaulted, a 3x12 slope and has eight recessed lights all through. I've experienced leaks in many locations With this area of your home, the leaks happen with the thaw and refreezing. It obtained the point final year wherever I needed to shovel the whole roof immediately after Just about every snow tumble.
Q. "You say 'You do not need an interior vapor barrier,' but You furthermore over here mght say that 'You will need a excellent air barrier on both sides of your fiberglass batts.' The latter would turn into an inside vapor barrier not so?"
Q. "I've a short while ago attained use of low-cost roofing polyiso -- black backing on either side. My emotion is that putting this backing against the rafters in touch with that vented air might be inviting a mold dilemma, and if i experience it towards the room i eliminate the radiant barrier."
Air flow channels are established by setting up a material that can preserve a separation (an air hole) among the insulation plus the roof sheathing.
We will give it a try. Present is a fourteen year outdated roof with two" of shut mobile roofing foam advice with an acrylic elastomeric coating.
Until a short while ago, building codes needed look at here that insulated sloped roofs incorporate air flow channels immediately under the roof sheathing. Quite a few builders even now observe this time-examined technique.
If you'd like a vapor-permeable materials that is still an air barrier, select fiberboard sheathing. But use caulk around the perimeter, and tape with the seams, To make certain that the material is put in within an airtight manner.
Superb report and discussion. I've a question about an existing unvented attic assembly. The rafters are 2x4's along with the bays concerning them are totally loaded with closed mobile spray foam. I would like to insert two 1in layers of polyiso in the direction of the inside of attic after which address with a vapor open membrane to airseal the assembly.
The R worth of your Reduce'n'cobbled foam + exterior foam must be at least 40% of the middle-cavity R worth for dew issue Handle for the foam/fiber boundary in zone 5. If It is really developing a tiny bit shy of that before including the outside foam it's actually not an enormous deal while in the short term, but if it's going to be five-ten years before re-roofing to raise the foam-R to over forty% of the overall It can be worth using vapor barrier latex primer to the gypsum board, or a smart vapor retarder among the gypsum board & fiberglass.