I've an unfinished attic, with cathedral ceiling, no insulation right now. in 5-10years we might be including dormers, but Meanwhile i want to add insulation and drywall in the simplest, most reversible/salvageable method. My approach is to hang two layers of two inch polyiso underneath the rafters, taped with staggered seams leaving the rafters empty, so effectively a vented assembly. I have extra blocking to the ground joists and is likely to make the polyiso steady within the knee walls. I believed I'd include furring strips in addition to the insulation then dangle drywall, thinking that the furring strips would make an airgap, making it possible for the foil to work as a radiant barrier.
My impression is that the steep aspect of a mansard roof is usually a roof. This can be especially true if the outside on the sloped assembly is finished with roofing.
We actually Do not know if these roofs have right vent channels, or which kind of vent baffles (if any) had been applied to maintain the ventilation hole in between the highest of the fiberglass insulation as well as underside of your roof sheathing.
[Editor's Notice: Monthly bill Rose just despatched me the next opinions in an e-mail; he involved his permission to put up the opinions.]
November eighteen, 2011 Graphic one of 3 A leaky ceiling doomed the roof sheathing. The ceiling of this ten-year-outdated house was Lower for an electrical box, and also the outsized hole was hardly ever caulked. Moisture-laden air entered the rafter bays by these cracks. If the moisture encountered chilly roof sheathing, it condensed, bringing about dampness accumulation and decay. (The rubberized membrane during the Picture was utilized as A brief patch for any hole during the roof, and didn't add on the failure mechanism.) Image Credit: Peter Yost A leaky ceiling doomed the roof sheathing. The ceiling of this 10-12 months-previous residence was Reduce for an electrical box, as well as outsized gap was never caulked. Humidity-laden air entered the rafter bays as a result of these cracks.
A. It makes sense for you since it meets your preferences. As that you are aware, it isn't an ideal approach to insulate your roof assembly. But you have got described it as a temporary prevent-gap evaluate.
Your prepare to setup 8 inches of rigid foam is a good a person, but you may be able to install thinner foam when there is a persuasive purpose to take action. Obviously, 8 inches of rigid foam has a higher R-value, and will execute improved, than the usual thinner layer.
Q. "I have already been utilizing rigid breadboard design expanded polystyrene inside the rim joists and considered the exact same can be put underneath the sheathing involving the rafter bays."
Recessed can lights acquire up space which need to be crammed with insulation; they offer off heat, producing thermal hot places as part of your insulated roof; and they leak air. They ought to be faraway from your ceiling and deposited before a relocating steam roller.
To forestall moist interior air from getting in contact with chilly surfaces close to the ridge, You'll need a true air barrier and a real insulation layer. The appropriate way to repair this issue is to reveal the rafter bays -- possibly from above or beneath, It truly is your decision -- and pull out the fiberglass insulation. Put the fiberglass inside a dumpster. Then fill the rafter bays with spray polyurethane foam.
The air leakage that Dana outlined would maintain your roof dry, but would undermine its thermal efficiency.
I have a partial cathedral ceiling during the finished attic of my home in zone 4 (TN). Each slope of the roof is divided around in thirds by 3 distinct situations: knee walls in the outer thirds, "cathedral" ceiling in the middle thirds, along with a vented "attic" in the center 3rd more info here using a ridge vent - a common circumstance with completed attics, at the least close to right here. I have a big trouble in the summer with overheating. The insulation just isn't Performing very well since it was poorly insulated with just R-19 fiberglass batts between the rafters and not using a air flow baffle or satisfactory soffit venting and only r-19 blown to the "attic Place". Furthermore, my upstairs HVAC ducts are operate inside the definitely sizzling "attic" Place beneath the ridge. According to what i haved discovered from various posts listed here, my planned Remedy should be to cathedralize the entire roof, eave to ridge: put in continous air-restricted site-developed 2" vent channels applying foil-confronted polyiso board (as suggested in ), setting up continual soffit vents to drastically Increase the airflow from soffit to ridge, generating an air-tight ceiling beneath the rafters, and, most of all, convey the ductwork inside the conditioned envelope.
My perception is if we are worried about air leakage compromising the insulation's performance, vent channels are problematic.
No matter whether you decide to really make it vented or unvented, get the small print right — mainly because each individual cathedral ceiling gives opportunities to produce major blunders