Your system to setup eight inches of rigid foam is an effective a single, however you could possibly put in thinner foam when there is a powerful purpose to take action. Certainly, eight inches of rigid foam has a better R-worth, and can perform improved, than the usual thinner layer.
The main flaw in this roof looks to be the ice and drinking water membrane at the very best position while in the rafter bays. Would just standard felt paper have permitted ample humidity to dissipate throughout the roof sheathing averting rot?, I form of doubt it.
I am with Martin on this one, your detail is labor intense for minimal if any attain in my opinion. The vent channels we describe can be achieved after the roof is on in the underside (dry side). For the people of us developing in a cold climate this can be a enormous benefit, we expend as tiny time as is needed to the roof.
for an unvented construction with no insulation above the sheathing, what about utilizing Wooden fibreboard in between the rafters directly underneath and in connection with the sheathing? All gaps involving the boards and the rafters full of growing foam / sealant. You could potentially then address the rafters with rigid foam to convey your insulation up to expected R level and lessen the risk on the rafters and sheathing, and then put in your airtight drywall beneath this.
Does this strategy audio as successful as vent channels manufactured on The within with the roof sheathing? I'm battling to find out why this would not do the job in addition or in pretty much a similar manner being an in-board web page-crafted vent channel. It really is primarily just like a rain display or vented cavity, very same as to the walls. Any feelings on this?
I do not know very well what you suggest by "unveiled." In zone three, you will need at the very least R-thirty of insulation (which means six inches of XPS). Upon getting installed R-30 of spray foam or XPS, you are finished. You are able to depart an air Area involving the bottom of your foam along with the drywall If you need.
I am not a fan of total peel-and-stick roofs, for several different good reasons. But your program will probably be high-quality. Just Guantee that your roof sheathing is dry about the day you put in spray polyurethane foam -- because the sheathing will not be drying great site very much in both course immediately after It is really encapsulated amongst peel-and-adhere membrane and spray foam.
Thanks - This really is new design, I am the designer / builder, and the more I check out it, I am liking all rigid - much less fussy. The best layer of rigid around fluffy can make my eave far too thick anyways. The air barrier for that T&G ceiling is actually the sandwich of felt and taped three/8" CDX.
"When you have set up the code-mandated thickness of rigid foam earlier mentioned your roof sheathing, you’re free of charge to set up as much fluffy things as you'd like among the rafters."
Contemplating it by means of on my Cape, I'd prefer to return to the method you explain; make the air barrier bounce again inside of on the wall leading plate, vent the sloped ceilings that has a site-constructed vent channel between the rafters, and go back to a flat ceiling on the next flooring, applying gable wall vents to vent an unconditioned attic.
I'm sorry being the bearer of terrible news, nevertheless the sections of roof which can be insulated with six inches of fiberglass and inside polyethylene weren't insulated correctly. In People sections, the roof sheathing is susceptible to moisture accumulation and rot.
. Unvented roof assemblies are Harmless. The main reason that lots of people put in ventilation channels over the rigid foam is mainly because they live in places with a great deal of snowfall, and they like a "cold roof" to reduce ice damming complications. Many thanks for your remark. I'll edit my posting to test to explain any ambiguity on this difficulty. .
Your weblogs on this matter are actually exceptionally helpful And that i appreciate your suggestions. ( I do analyze prior to I post issues : )
I believe that most contractors would be worried about the buildability of the strategy. The Image exhibits a small-slope roof about a flat ceiling; this allows staff to stand to the ceiling joists.