You explain your proposed air barrier as "taped felt." I don't Feel asphalt felt could be efficiently taped, and I do not are convinced asphalt felt helps make a very good air barrier.
No matter if you select to really make it vented or unvented, get the small print proper — because each cathedral ceiling delivers alternatives for making massive errors
Ken's element (#10) does a great position of cold local climate safety. It's got what we are trying to find: Fantastic airsealing at the interior, fluffy stuff in the middle, and great drying channels for water vapor at the highest. By switching from a very low permeability sheeting to your substantial permeability membrane (at top) with venting over, there is not any a lot more concern for roof rot though at the same time wind washing is prevented from the bays via the air & water limited membrane with taped edges and seams. It appears to me for being a really long lasting assembly.
Code interpretations are subject matter for the willpower of your local making inspector. In the long run, it will not issue what I do think -- what matters is exactly what your neighborhood code Formal thinks. So check with her or him.
Dan Reams, thanks for the comments. I also live in snow region in close proximity to Yellowstone Nationwide Park. I normally have nicely about three feet of snow on my cathedral roof. I feel the dew point is often in the snow rather then inside the roof. The R worth of the snow is commonly close to the R price of the roof. This may lead to huge ice dams. A straightforward thermal analysis shows that You can not set a simple quantity of insulation from the roof to forestall the ice dams and go the dew level into the roof.
Magic bullet status is page not really achieved. It is a style and design for just a very low over here slope roof. It really is very much along the strains of Doug McEvers utilization of high perm fibre board to make vent channels earlier mentioned dense packed cellulose.
Should really I treat the flat roof like a cathedral ceiling and select spray foam (or board), fiberglass, and no humidity barrier?
I concur with you: I would like to see additional information on this difficulty. I'm not aware about any failures that have occurred in appropriately dense-packed unventilated rafter bays.
I haven't got loads of place higher than or beneath the roof structure for insulation / venting. Would a flash / batt unvented More Info assembly get the job done beneath the single sheathing deck? My insulator has accomplished Numerous of these domestically.
Q. "Have you been indicating that increasing ventilation to that next story attic would really be a bad thought, if we carry on the foam about all the next Tale gable roof, and alternatively we should allow it to be absolutely unvented?"
1. You ought to get an engineer to evaluate the security of one's 2x4 rafters. "Furring down with 2x2s" won't Increase the capability within your 2x4s to bear the snow load. It's attainable that an engineer will recommend you to definitely sister 2x8s or 2x10s on to your existing 2x4 rafters.
Should your weather will not be as well extreme It really is most likely all right to get just the R-ten foam around the structural steel, Whilst there is certainly some danger the steel could sweat in chilly climate. I am assuming In addition, you intended to insulate the 2x12 joist bays to Get the total R-price to an inexpensive amount.
In the ultimate summary it reads: "In case you are using fluffy insulation, you may need two air obstacles: a single underneath the insulation, and just one previously mentioned the insulation.
an air barrier. If you intend to put in EnGard insulation batts in an unvented cathedral ceiling, You'll have to own an important layer of rigid foam insulation earlier mentioned the roof sheathing.