Your approach will perform fine, so long as the layer of rigid foam along with your roof sheathing has an R-value of no less than R-twenty. Should you be applying XPS, you would like at the least four inches of foam. If you are making use of polyisocyanurate, you require not less than three inches of foam.
Doug I agree, a lot of wrongs "overthinking" and overdoing. I when had to resupply a health care provider constructing an plane with dozens of AN plane bolts mainly because they had been tightened to the point of breaking the bolts. Considerably less is more occasionally... Along with the KISS rule.
As The top of our regional HBA, I have strenuously identified that foam around a vented flat roof assembly will not present the insulation values promised. Some builders have proposed they could only seal and stucco more than the stucco vents and reduce the ventilation.
If the weather isn't much too significant It truly is almost certainly okay to have just the R-ten foam around the structural metal, Even though you will find some hazard which the steel could sweat in chilly climate. I'm assuming Additionally you meant to insulate the 2x12 joist bays to get your overall R-worth to a reasonable amount.
Q. "I've a short while ago attained use of cheap roofing polyiso -- black backing on each side. My feeling is the fact that Placing this backing from the rafters in connection with that vented air may be inviting a mildew challenge, and when i confront it in the direction of the home i lose the radiant barrier."
You are right that such a roof assembly is not going to dry to the interior. But it is not alleged to. I would tape the polyiso -- the tape is not going to induce any troubles.
I've a fifty year-aged seasonal cottage in a very northern local climate. The easy six/12 gable roof is made up of precise 2x6 rafters (24" oc), sheathed with one/two" plywood and covered with asphalt shingles. There is no insulation within the ceiling and I believe tiny to no powerful insulation within the 2x4 partitions. In the summer the warmth get inside will make residing Pretty much unbearable. I think that the most important bang to the buck can be to handle the ceiling insulation problem initially, but want to retain the inside visual appearance.
In order to set up a combination of closed-cell spray-foam around the underside on the roof sheathing and air-permeable insulation concerning your rafters — an method from time to time identified as “flash and batt†— the creating code needs that spray foam (or, arguably, rigid foam insulation) be “utilized in direct connection with the underside in the structural roof sheathing†and which the foam insulation satisfy the necessities “laid out in Desk R806.
On an unrelated subject: read this post here The Cold Climate Housing Research Centre has manufactured a online video (beneath) showing 1 technique of setting up an insulated cathedral ceiling. The strategy shown during the video is especially suitable for builders in climates matter to ice dams.
and not less than within the ridge, in which joints are shut with each other, to can foam with low expansion flex foam Thoughts I've are
My impression would be that the steep facet of the mansard roof is actually a roof. This is often especially true if the outside with the sloped assembly is concluded with roofing.
On the subject of fluffy insulation, are there any sources it is possible to refer me to which deal with the differences involving lower, medium and large density fiberglass batt insulation from your standpoint of loss of R-Benefit as a consequence of wind-wash (whether due to air infiltration or convection as a result of considerable temperature variances entrance to back)?
Need to i totally assist sheathing seams parallel into the ridge line, for sheathing above an air gap? Wouldn't that isolate the air below Every sheet of sheathing, and is that okay?
Keep in mind: if you choose to set up rigid foam on top of your roof sheathing, don’t set up air flow channels underneath the roof sheathing; both of these procedures are incompatible.