Dan Reams, many thanks for your remarks. I also reside in snow country around Yellowstone National Park. I usually have well around three ft of snow on my cathedral roof. I think the dew issue is commonly inside the snow rather than while in the roof. The R value of the snow is frequently near the R value of the roof. This can result in large ice dams. An easy thermal analysis displays that you cannot place a simple volume of insulation from the roof to avoid the ice dams and move the dew position in to the roof.
It is quite attainable to structure an unvented insulated roof assembly that performs perfectly, so long as you get the details proper.
The higher density fiberglass is so considerably more dense than the medium and minimal density fiberglass that it seems like it must reduce the probable for convection within the batts, but at 2 to three situations the cost of medium density fiberglass batts the achieve can be nominal and never definitely worth the additional Charge. Thanks for sharing your know-how,
Given that I've discussed the best way to make it happen, I will also let you realize that many people have finished Whatever you suggest.
To comply with the code -- also to undertake a making system that's considerably less risky -- you'll want to possibly consist of ventilation channels or you might want to install a layer of spray foam over the underside in the roof sheathing, adhering to the recommendations described inside the article on this site.
sips are excellent but in the coldest of climates they've encountered issues. google difficulty applications in alaska - apparently a gaggle of residences there were crafted but not sufficient attention to detail with the plumbing and roof vents have been taken into account (Definitely air tight foamed in penetrations), mated panel seams and fastener punctures triggered the best degree osb to rot. Of course The complete roofs required substitution.
I have a fifty year-previous seasonal cottage in a very northern weather. The easy 6/12 gable roof is composed of real 2x6 rafters (24" read more oc), sheathed with one/2" plywood and covered with asphalt shingles. There is absolutely no insulation from the ceiling and I think little to no effective insulation in the 2x4 walls. In the summer the heat acquire inside helps make dwelling Nearly unbearable. I suspect that the greatest bang to the buck could well be additional hints to deal with the ceiling insulation difficulty very first, but would want to manage the interior overall look.
Naturally, you may still have thermal bridging throughout the rafters. But you won't have any moisture issues.
I am acquainted with that method and have used it on former double partitions with flat ceiling/ truss roof assemblies. Labored superbly.
"R-19 batts are quite air permeable, and on extended unobstructed rafter bays you might have quite a stack result. It isn't going to take a massive quantity of air leakage to supply some drying there. Also, In the event the batts are unfaced or kraft-faced, the drying towards the inside could be significant.
The home is at about four,five hundred ft. We only get about 3' of snow a yr and it almost never stays within the roof for more than week a few situations a 12 months. I am on go an exceedingly tight funds, just endeavoring to make the location livable. Any tips are welcome.
Q. "You say 'You do not need an interior vapor barrier,' but In addition, you mention that 'you need a superior air barrier on either side of the fiberglass batts.' The latter would turn out to be an inside vapor barrier not so?"
I applied to work to be a roofer, and roofs which might be solely included with Ice & H2o Shield make me anxious. I see this type of layout as lazy and likely problematic.
one. You don't need an interior vapor barrier. Inside a warm humid climate, the vapor travel is usually from the outside towards the inside (assuming your creating is air conditioned). Should your creating isn't ever likely to be air conditioned, the vapor drive will nonetheless be from the exterior to the interior, but there won't be A great deal vapor travel.