In order to set up a mix of closed-cell spray-foam on the underside from the roof sheathing and air-permeable insulation in between your rafters — an solution often called “flash and batt†— the making code involves that spray foam (or, arguably, rigid foam insulation) be “utilized in direct connection with the underside on the structural roof sheathing†and that the foam insulation satisfy the requirements “laid out in Table R806.
Chuck- Google "reclaimed foam." There are a selection of sellers of reclaimed foam in MA. You'll preserve a bundle and aid the World to boot.
You can skip the tape on the very best layer of plywood to exact some time and money. That's most likely what I'd personally do if I ended up you. Having said that, there's no damage in taping the seams of the very best layer of plywood.
BTW, for the foam style, I'm leaning towards XPS due to the fact one) I possess the effect that ISO is rather fragile, like if it gets in the slightest degree moist, and a couple of) the opportunity of long term outgassing with ISO. Ideally any these outgassing would go upwards and outwards in lieu of downwards into the house inside, but the possibility that it might outgas into the inside definitely problems me.
Unbelievably beneficial (five*) thread. So, if you have to use fiberglass insulation batts, therefore you dont have entry to spray foam or closed mobile boards, what do you need to do? I assume The true secret is to really make it unvented and include in other air-impermeable layers. I am about to insulate a different all-metallic cathedral pitched gable roof within the Caribean. The system should be to fill the cavity between the 4" Z-purlins with R-eleven batting (vapor facet going through the residing Room). For extra heat conduction resistance we plan to roll An additional thinner (filleted?) layer of this batting excessive from the purlins (ie concerning the purlins and also the sheeting).
Remember: Because your roof assembly is dry, does not imply it can be perfectly insulated. Your assembly could have substantial air leaks that work as thermal bypasses. (Or not. It truly is difficult to notify with no internet site go to.)
In case you go in advance along with your system, you should incorporate a sensible vapor retarder on the inside aspect of the assembly, to minimize the transportation of dampness from the inside for the sheathing.
Inside a word, no — the code explicitly forbids this process. Cellulose can only be Utilized in an unvented roof assembly when there is an satisfactory layer of rigid foam higher than the roof sheathing Full Article or an ample layer of shut-mobile spray foam beneath the roof sheathing. Cellulose by itself won’t get the job done.
I feel you signify this: Your cathedral ceiling is presently uninsulated. While you are indoors wanting up, you could see your rafters. Above the rafters you are able to see a layer of boards. Is accurate?
My feeling is that if we've been concerned about air leakage compromising the insulation's usefulness, vent channels are problematic.
Utilizing ventilated nailbase panels is a perfectly good way to build a cathedral ceiling. The identical regulations utilize as when applying SIPs: make certain that the seams are sealed to be as airtight as you may make them, and be sure that the entire R-value of your roof assembly satisfies or exceeds minimal code R-price necessities.
I'm accomplishing precisely the same element on my new construction. I bought the insulation from David Volpe @ NationwideFoam.com. There's a area in Framingham, MA. I purchased quite a few tractor trailer masses to insulate my residence and barn for an exceptionally, pretty affordable cost.
To prevent moist inside air from making contact with cold surfaces close to the ridge, you need a true air barrier and an actual insulation layer. The appropriate way to fix this issue is to reveal the rafter bays -- either from over or under, It truly is your preference -- and pull out the fiberglass insulation. Set the fiberglass in a dumpster. Then fill image source the rafter bays with spray polyurethane foam.
Sorry, Martin, I now know that "new construction" won't essentially suggest "new home to get designed", and "an unvented attic, with R-fifty underneath the roof" ought to have been "an unvented attic, with an R-50 roof'. Because It really is obvious to me does not imply It can be very clear to Anyone else.