While in the absence of the airtight ceiling, roof ventilation can do extra hurt than superior, due to the fact air motion in rafter bays can persuade indoor air to leak by ceiling cracks.
Like most mansard roofs, your roof is unvented. Your mansard roof has diverse sections -- the steep sections with the perimeter, and the low-slope part in the middle. Every one of these sections must be insulated in an analogous way, due to the fact every one of these roof assemblies are unvented.
Given that I have described the right way to get it done, I may also Allow you to understand that A lot of people have carried out Everything you propose.
In the event your climate is not really far too intense It is really most likely okay to have just the R-10 foam more than the structural steel, although there's some danger that the metal could sweat in chilly temperature. I'm assuming Additionally you intended to insulate the 2x12 joist bays to Obtain your total R-worth to a reasonable amount.
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Otherwise, he will not reach refuse to put foam higher than the sheathing, which would be superior and much less expensive than fitting it concerning the beams.
If you choose to set up open up-mobile spray foam as an alternative to shut-cell spray foam, your roof assembly will be able to dry rather to the inside. Just make sure that the spray foam layer is thick adequate to keep your rafter bays higher than the dew position over the Winter season.
Many thanks for finding the thread previously mentioned...note that in write-up #17, Robert Riversong talks in regards to the "vented about roof". I agree along with Clicking Here you that this process justifies some focus for cathedral ceilings.
We program to convert to an improperly vented cathedral ceiling to an unvented one particular. Sealing up the soffit vents is really a no-brainer. What is actually The simplest way to take care of the ridge vent? Thanks!
You will be proposing an abnormal approach to insulating your roof. If I recognize you effectively, you intend to set up EPS amongst the tops of your respective roof trusses as well as your roof sheathing.
Q. "For an unvented development without insulation earlier mentioned the sheathing, what about using wood fibreboard between the rafters directly under and in connection with the sheathing?"
I feel you mean this: Your cathedral ceiling is presently uninsulated. When you find yourself indoors on the lookout up, you can see your rafters. Over the rafters you can see a layer of boards. Is the fact that accurate?
You explain your proposed air barrier as "taped felt." I don't think asphalt felt can be properly taped, and I do not imagine that asphalt felt makes a very good air barrier.
Builders clear up this issue by furring down or scabbing on supplemental framing below the rafters to deepen the rafter bays.