I'd personally incorporate to Martin's listing of resources for rafter vent channnels, fiberboard sheathing. I take advantage of I joists for vented cathedral ceilings and staple 1/two" fiberboard to the bottom of the top cord on the I joists. It can be ripped over a desk observed and installs immediately, fiberboard does Have a very superior perm score and should allow for tiny amounts of dampness to go through in to the vent space.
If a constructing inspector insists that you install some kind of interior “vapor barrier,†it is possible to normally install a wise vapor retarder like MemBrain to satisfy your inspector.
A. The air barrier is usually a vapor barrier, since the rigid foam can be likely to be described as a vapor barrier (or close to it) in almost any case.
Thanks - That is new construction, I am the designer / builder, and the more I examine it, I'm liking all rigid - a lot less fussy. The highest layer of rigid above fluffy would make my eave far too thick in any case. The air barrier for your T&G ceiling is in fact the sandwich of felt and taped three/8" CDX.
November 18, 2011 Picture one of three A leaky ceiling doomed the roof sheathing. The ceiling of the 10-yr-old property was Slice for an electrical box, as well as the oversized hole was under no circumstances caulked. Humidity-laden air entered the rafter bays as a result of these cracks. Once the moisture encountered cold roof sheathing, it condensed, leading to humidity accumulation and rot. (The rubberized membrane while in the Photograph was made use of as a temporary patch for any gap during the roof, and didn't add for the failure system.) Impression Credit rating: Peter Yost A leaky ceiling doomed the roof sheathing. The ceiling of the 10-yr-previous household was Slash for an electrical box, as well as outsized gap was never caulked. Dampness-laden air entered the rafter bays by means of these cracks.
Insulated cathedral ceilings are a comparatively the latest phenomenon. The trend for insulated cathedral ceilings (and terrific rooms) actually took off within the seventies and 1980s, when illustrations commenced popping up like mushrooms following a heat rain.
Preferably, you would like to have an airtight barrier over and below your fiberglass batts. If you can obtain All those two air boundaries, then wind-washing is not an issue inside a roof like yours. (It might be within a vented unconditioned attic, needless to say, especially near the soffits.)
Thanks to your reaction Martin. Would you continue to be joyful to utilize that unvented approach for any renovation scenario exactly where There is certainly non-breathable membrane (eg bitumous 'felt') over solid board sheathing?
Thanks all over again. The roofer agrees that 2x4 framing to lift the height over the vented attic could well be a workable Resolution to match up the roof strains.
You happen to be correct that this kind of roof assembly is not going to dry to the inside. But it isn't alleged to. I'd personally tape the polyiso -- the tape won't lead to any difficulties.
If you like, you are able to Track down your air flow channels on top of the roof sheathing as an alternative to beneath the roof sheathing. If you choose to do this, Guantee that any roofing underlayment that you install over the roof sheathing is vapor-permeable — for example, #15 asphalt felt, VaproShield SlopeShield, or Solitex Mento — and that your local creating Office from this source accepts this approach to roof venting.
If you need to put in a combination of rigid foam on top of your roof sheathing and air-permeable insulation involving your rafters, you might want to be sure that your rigid foam is thick plenty of to maintain your roof sheathing earlier mentioned the dew place.
If you install 2x4s (or 2x3s on edge, mounted with very long screws) perpendicular towards the rafters, you might deal with most of the thermal bridging issue without the must incorporate a layer of rigid foam.
JB- I really ought to post sketches as Ken did. It will likely save some hassle. For me this was harking back click here now again on the compact roof string.