I'm with Martin on this a person, your element is labor intensive for very little if any attain for my part. The vent channels we describe can be carried out once the roof is on within the underside (dry aspect). For people of us building in a cold climate this is the big advantage, we spend as small time as is necessary over the roof.
Having said that, I do think you might be Mistaken regarding your asphalt felt; I doubt Should the felt is impermeable to water vapor. Most sorts of asphalt felt are somewhat permeable -- usually 5 perms when dry and as much as 60 perms when soaked.
for an unvented development without having insulation previously mentioned the sheathing, how about applying Wooden fibreboard concerning the rafters directly under As well as in connection with the sheathing? All gaps between the boards plus the rafters full of expanding foam / sealant. You may then address the rafters with rigid foam to deliver your insulation as much as expected R amount and decrease the hazard to the rafters and sheathing, and afterwards put in your airtight drywall underneath this.
It seems if a single ended up to implement dense pack cellulose inside of a vented cathedral ceiling the vent channel substance ought to be rigid enough to face up to the force.
By Martin Holladay
If you wish to use just one kind of insulation in unvented rafter bays, that you are limited to spray polyurethane foam. Yet another possibility, certainly, is to make your roof with structural insulated panels (SIPs).
I have listened to a lot of reports of homeowners with problematic SIP roofs installed in the 1980s -- Many of these roofs are now rotting within the seams on account of condensation of moisture from exfiltrating interior air -- to feel cozy recommending a SIP roof.
If this were being my navigate to this website dwelling, and if the fiberglass batts are seen, I might pull most of the insulation out of some rafter bays to find out what's up there.
You say "You do not need an interior vapor barrier," but Additionally you express that "you need a excellent air barrier on either side of your fiberglass batts." The latter would turn into an interior vapor barrier not so?
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If you are doing when you propose, you should achieve an addition gain from the R-20 insulation over the roof sheathing. That said, the tactic you describe would not meet code demands for new design, simply because ideally any insulation used to nutritional supplement the rigid foam above the roof sheathing has to be in immediate connection with the underside with the roof sheathing.
one. Your suggestion is just a slight variation on the detail that is now talked over in my web site, specifically cellulose installed having a vent channel in between the very best of your cellulose and the roof sheathing.
A. Possibly approach will work, provided that you get not less than the bare minimum code R-benefit for your roof, and provided that you use development techniques that concentrate to airtightness.
That looks very attractive: go with R-30 on the underside on the deck at our home making use of a combination of fiberglass batts and XPS as I described previously mentioned, then incorporate a further R-ten (2" XPS) on the very best aspect after we tear down and re-roof? Unfortunately that sounds like It truly is too straightforward.