Your prepare will operate good, assuming that the layer of rigid foam on top of your roof sheathing has an R-price of at the very least R-twenty. Should you be applying XPS, you require at the very least 4 inches of froth. Should you be utilizing polyisocyanurate, you may need at the very least three inches of froth.
Should you go in advance using your prepare, you must incorporate a sensible vapor retarder on the inside aspect in the assembly, to minimize the transportation of dampness from the interior into the sheathing.
Our cooler mornings could make the interior of my steel roof sheeting to sweat slightly since it will be in connection with the hotter unvented fiberglass-insulated purlin "cavity" beneath. As soon as our hot Caribbean sunshine begins to kick in I would like this humidity to dry and/or diffuse out of the cavity, through the gypsum sheeting, in the cathedral residing space underneath, to then be blown from my 4x3 gable window. A vapor barrier would completely retard this process.
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Even though the GBA website by now consists of several articles on the topic, we keep on to receive frequent questions on The obvious way to insulate a cathedral ceiling.
Am i able to get some far more commentary over the "entire roof" of Ice & Water Defend? I do think this had little or no to perform Along with the failure. The key reason why why I question is I have an identical "complete roof" layout arising, Nonetheless, the rafter bays are all straight operates with soffit vents, constant vent baffles (one/2" plywood) and ongoing ridge vent. Dense pack cellulose, two" XPS under 2x10's, air tight drywall (XPS can be sealed up far too).
A. Both tactic will operate, providing you get at the least the bare minimum code R-worth for your roof, and providing you use building methods that pay attention to airtightness.
Doug... For a few rationale I did't see your submit #17. Appears like two of us at the least Imagine there could be a really easy low-cost Resolution.
On an unrelated topic: The Chilly Weather Housing Analysis Centre has made a online video (under) displaying a person means of creating an insulated cathedral ceiling. The method proven from the online video is particularly appropriate for builders in climates subject to ice dams.
"R-19 batts are very air permeable, and on extended unobstructed rafter bays you might have quite a stack outcome. It isn't going to take a big quantity see this website of air leakage to offer some drying there. Also, When the batts are unfaced or kraft-faced, the drying toward the inside might be substantial.
It looks like a wonderful prepare. Based on what sort of rigid foam you select, you'll end up having insulation while in the variety of R-sixteen to R-24. While which is a lot less than code requirements, It is really Significantly, much better than what you've now.
If you wish to use just one form of insulation in unvented rafter bays, you are limited to spray polyurethane foam. A further possibility, of course, is to make your roof with structural insulated panels (SIPs).
I employed to work for a roofer, and roofs which are entirely included with Ice & H2o Protect make me nervous. I see this kind of style as lazy and probably problematic.
Because the point with the string is generating roofs that do not fall short, there are likely to be assemblies that really work well but are a little bit of a departure. If we had the very best tactics that we could at any time picture, now in hand and on position web sites, we would not be in this article (at GBA) and Martin would have far less to carry out.