I'd personally include to Martin's list of elements for rafter vent channnels, fiberboard sheathing. I use I joists for vented cathedral ceilings and staple one/2" fiberboard to The underside of the very best wire from the I joists. It could be ripped on the desk saw and installs quickly, fiberboard does Possess a superior perm ranking and could allow smaller quantities of dampness to go through into your vent House.
If you'd like to build an unvented insulated roof assembly, you may have two options: (a) You are able to increase rigid foam to the outside aspect of one's roof sheathing, followed by a second layer of roof sheathing and new roofing, or (b) You could insulate the underside within your roof sheathing with spray polyurethane foam.
Your caveat is suitable and conservative. For your vast majority of builders, nevertheless, the code demands will preserve roofs free of troubles.
When your local climate is not really much too critical It really is likely all right to get just the R-ten foam around the structural steel, While you can find some threat that the metal could sweat in chilly weather conditions. I am assuming In addition, you meant to insulate the 2x12 joist bays to get your full R-worth to a reasonable amount.
I agree along with you: I might prefer to see more information on this issue. I'm not aware of any failures which have occurred in thoroughly dense-packed unventilated rafter bays.
You are describing a cathedral ceiling that comes with all achievable mistakes. There was no notice to air sealing. The worst possible insulation was used (fiberglass). Along with the roof assembly is unvented. So it is actually no surprise that you're observing condensation.
Except 1 uses Intense treatment with the warm aspect air barrier and this involves realizing that every one fastener penetrations are sealed at the same time you ought to presume some air movement. The set up referred to listed here While using the ice and water defend under the shingles clearly manufactured an even better air barrier than whatever was on the warm side.
A. This is the grey place within the making code. It truly is safe to say that no professional insulation contractor would use that system, which Lots of people connect with "Reduce and cobble.
Re: the air barrier being put previously mentioned the pine T&G ceiling and down below the foam, would you endorse that we use a little something which is both equally an air barrier along with a vapor barrier? Or can it be essential to ensure that the product or service we pick out isn't a vapor barrier, to make sure that any dampness that gets into your roof assembly can dry to the inside?
Most building codes call for one square foot of Internet cost-free air flow location for every 300 sq. ft of attic floor location, assuming that half in the air flow openings can be found within the soffit, and fifty percent along the ridge.
In the ultimate summary it reads: go to my site "For anyone who is making use of fluffy insulation, you would like two air limitations: a person down below the insulation, and 1 higher than the insulation.
On the other hand, in certain parts of the place, specifically in the Northeast, insulation contractors are actually dense-packing unvented rafter bays with cellulose For a long time. As the process has deep roots in New England, a lot of developing inspectors settle for this sort of installations.
My perception is the fact that if we are worried about air leakage compromising the insulation's usefulness, vent channels are problematic.
In the choice, if we can't do a ventless roof that way, can we obtain our whole insulation site here demands by combining the above and below deck R-Values if we prime it all which has a vented more than-roof? Thanks for your time and efforts plus your advice! Dan