Your program to setup eight inches of rigid foam is a good just one, however you may be able to put in thinner foam if there is a persuasive cause to take action. Not surprisingly, 8 inches of rigid foam has an increased R-benefit, and will conduct improved, than the usual thinner layer.
Needless to say, occasionally you'll want to strategy forward to be sure that your rafters are sized sufficiently to permit for insulation and venting. For more information on satisfactory tips on how to insulate small-slope roofs, see this information: Insulating Low-Slope Residential Roofs.
If you select not to extend the rigid foam over the portions of your roof that have a conventional vented attic, your builder (or an architect) can come up with a trim detail that you may be able to Stay with.
I have insulated the edges with R-19 fiberglass and now I'm thinking: was that a miscalculation? It's craft paper and I used to be planning with a plastic sheet in addition, really should I skip that?
Could you please provide a element of earlier mentioned sheathing ventilation employing a continuous Ice&Drinking water membrane, and metal roofing for any mixed weather? Thanks
Ken's detail (#ten) does a fantastic job of chilly local climate basic safety. It's what we are looking for: Fantastic airsealing at the inside, fluffy stuff in the center, and fantastic drying channels for h2o vapor at the very best. By transforming from the small permeability sheeting into a substantial permeability membrane (at prime) with venting earlier mentioned, there is absolutely no much more worry for roof rot even though simultaneously wind washing is prevented within the bays with the air & water limited membrane with taped edges and seams. It appears to me to be an exceptionally tough assembly.
Like Doug's style and design, the main focus is on developing a superior perm layer for drying to the exterior, that should nevertheless allow venting even though blocking wind washing inside weblink the fluffy things.
A. There's a code prerequisite to get a vapor retarder in some varieties of assemblies, but there's no need for just a vapor barrier. Your layer of rigid foam is by now a vapor retarder. No further more vapor retarding layer ought to be mounted.
Okay, I had been figuring that the whole with the rigid foam + cellulose had to be a certain R-value together and were pondering applying a lot less rigid foam. I have been studying about diverse varieties of cellulose. Given that I am putting in from earlier mentioned would a little something like stabilized cellulose function because it has a little water added?
The best strategy is to do all of the operate simultaneously: rigid foam higher than the roof sheathing (as proposed in the posting), and fluffy insulation underneath.
Martin, thanks to your fantastic and well timed guidance, we are actually headed towards an answer of rigid foam around the exterior with the ceiling. Thanks for pointing me In this particular new and enhanced route. We remain working out some facts, which include...
I would want to use the outside wall and roof sheathing as my primary air barrier; cdx plywood with all seams taped, which kind of forces me to help keep the roof venting in addition to the roof sheathing, when you explain in paragraph seven of this post. I'd wish to use Solitex Mento as being a permeable roofing underlayment, as well as a WRB on vertical walls, and 2 layers of cross hatched 1x4 strapping above roof ply and Mento; one particular running down the roof slope, nailed on the rafters, and the second run horizontally about them to assistance corrugated metal address roofing.
I do think you imply this: Your cathedral ceiling is presently uninsulated. If you find yourself indoors wanting up, you could see your rafters. Higher than the rafters it is possible to see a layer of boards. Is that accurate?
one. You don't need an inside vapor barrier. Inside a scorching humid climate, the vapor travel is often from the exterior towards the inside (assuming your building is air conditioned). If the setting up is not ever gonna be air conditioned, the vapor push will nevertheless be from the exterior to the inside, but there will not be A great deal vapor travel.