I am with Martin on this just one, your depth is labor intense for small if any gain in my view. The vent channels we explain can be done once the roof is on within the underside (dry side). For anyone of us making in a chilly local weather that is a big edge, we invest as little time as is needed about the roof.
We've chose to insulate on the exterior with the roof sheathing all the way across both sides on the gable roof, in order to match up the roof lines.
Now that I've explained the right way to do it, I will also let you realize that Many individuals have performed Anything you propose.
You should use Ice & Water Protect as an air barrier If you would like. But when you select to employ that item, you'll need to eliminate the asphalt felt so which the Ice & H2o Defend is usually adhered towards the roof boards.
A. You must only use an set up approach that your insulation contractor is aware of. In this article from the Northeast, numerous contractors would possibly fill your rafter bays using the dense-pack strategy following your new roof sheathing was mounted.
If you need to use just one form of insulation in unvented rafter bays, you're limited to spray polyurethane foam. Another probability, obviously, is to create your roof with structural insulated panels (SIPs).
Q. "I'm wondering if I must furr out the rafters for getting the desired thickness of spray foam, or if setting up some inches of polyiso foam for the underside with the rafters, following the spray foam, could do the job?"
The old Canadian guideline -- not less than two/three of the total R-price on the outside side with the vapor barrier -- can be a tough-and-ready way to address this question; it's also feasible to strategy the dilemma by doing a dew-point analysis or simply a WUFI Investigation.
Should I use airtight baffles or not, I don't see a means to have humidity escaping inside of a assembly with airtight baffles, fiberglass and xps on The within, regardless of what the dew stage might be within this assembly and possibly create condensation that can't evaporate without having air flow.
four. Once you have R-20 or R-twenty five of rigid foam along with your sheathing, you are able to safely insulate beneath your sheathing with Nearly almost any insulation you wish to use to provide your insulation approximately minimum code specifications.
Martin, many thanks. I just talked towards the roofer and he turned down the concept of only putting the foam about the relatives area cathedral ceiling. That Odd "jog" during the roofline, getting it quickly bump up 4" or eight" where the household area begins, in the course of the back facet with the roof, would defeat the concept of a continual slope for rain to come down when it hits the upper Element of that again roof. Therefore the four" or 8" height addition demands to carry on across the overall 2nd Tale roof line.
Next, is it possible to please ensure this: "If you wish to use only one sort of see here insulation in unvented rafter bays, that you are restricted to spray polyurethane foam."
Be sure the roof assembly is as near to airtight as you can also make it. If you're applying fluffy insulation, you need two air barriers: one under the insulation, and a person higher than the insulation.
Thorsten Chlupp is in a Substantially more challenging weather and he appears to be accomplishing fine with simple loose fill to the attic floor....naturally he is working with "sufficient" quantities (cellulose galore)and he has baffles near the soffit.