I thanks for this impeccably timed blog, as I am at present framing my semi-simple cathedral ceiling hip roof (with shorter ridge). I wish to describe my depth and try to grasp where I am on the proper observe and much more importantly, wherever I will likely have failures. Hope I can amuse a number of you...I really feel such as extra I attempt to deal with a concern, the greater of a concern it gets, And that i undoubtedly don't want to get terrific time, care, and element to aid the demise of my roof.
Like most mansard roofs, your roof is unvented. Your mansard roof has diverse sections -- the steep sections within the perimeter, as well as lower-slope segment in the center. These sections need to be insulated in an identical way, simply because most of these roof assemblies are unvented.
It is Secure to declare that an current house does not have very good roof air flow if there are no soffit vents or ridge vents. It is also Secure to express that, whether or not you can find soffit vents and ridge vents, the roof isn't ventilated if it incorporates valleys, hips, dormers, or skylights.
Thanks for your input. I see a stop by that has a structural engineer and 35 square of polyiso in my around foreseeable future.
You feel uncertain. By way of example, you wrote, "it's actually not vented in any way." But in my short article -- the short article on this website page, in which you posted your remark -- I wrote, "there are three ways to construct an unvented roof assembly." I then proceeded to clarify how to create such a roof. I claimed that it is feasible
The rationale to put the extra insulation in connection with the underside of the roof is usually that It really is not easy to validate that you've efficiently closed off all vents into the attic. But if you truly do reach performing that, there needs to be no difficulty. With a blower doorway can be done, however difficult.
Your plan to setup 8 inches of rigid foam is a good one particular, however, you could possibly set up thinner foam if there is a powerful cause to take action. Not surprisingly, eight inches of rigid foam has the next R-worth, and will carry out much better, than a thinner layer.
Thanks for finding the thread above...Take note that in submit #seventeen, Robert Riversong talks about the "vented above roof". I agree along with you that this process deserves some attention for cathedral ceilings.
The perimeters on the roof are included with asphalt shingled (GAF Slateline to be specific). It feels like I really should pull down the fiberglass and also have it spray-foamed ahead of I drywall.
You are proper that such a roof assembly won't dry to the inside. But it isn't alleged to. I'd personally tape the polyiso -- the tape would not cause any troubles.
Should you’re building a new dwelling, having said that, below’s my information: if you'd like to insulate with cellulose, help it become a ventilated roof by including air flow channels beneath your roof sheathing. Leaving out the ventilation channels is dangerous.
I'm addressing somewhat link various problem that I'd like some enter on. I'm developing a Vineyard tasting area within a masonry setting up (eight" monolithic concrete walls) in 4C/5B local weather zone in So. OR. I have received an uncovered 2x10 T&G ceiling around GLB purlins @ 5'oc, so I'm creating it from The underside up and the last layer to go on is the sheathing beneath the metal roofing. I had planned to install an air barrier around the T&G deck (taped felt) then body 2x8 @ 24"oc with significant density batts to fill the cavities, in excess of that is the sheathing underneath the steel roofing.
1. You don't want an inside vapor barrier. In the incredibly hot humid local climate, the vapor push is often from the outside toward the inside (assuming your setting up is air conditioned). When your building is not ever destined to be air conditioned, the vapor push will even now be from the exterior to the inside, but there won't be Significantly vapor generate.
As pointed out previously mentioned, we hope to exchange the roof this next calendar year. If so, at that time I'd prefer to up grade to either an unvented roof or if important a cold roof (a vented around-roof). (I don;t are aware that it matters in the equations, but we're investigating buying and setting up stamped steel shingles.