Vent Chute

April 18-28:  Icicles sparkling and draping from a roof on a vacay-snow-day is a beautiful sight, but when you know more you see trouble. You see heat loss, hidden pools of water, and stained ceilings.

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My super-insulated, super-airtight, super-vented roof will even out and slow down snow melt. Warm moist inside air won’t find a route through and condense on cold surfaces and soak insulation. If I worry about sealing up every single little-bitty gap now, I won’t have to worry about mold, mildew, or rotting structure later.

chute croppedA flat ceiling is easy to insulate and easy to ventilate. A sloped ceiling like mine takes extra steps. I’ll use eco-friendly cellulose, made from recycled newsprint. But there are two hurdles: it settles and drifts unless “dense-packed” into a cavity, and Code requires it be top-vented to allow any moisture migrating from below a route of escape. The usual solution is a manufactured “vent chute” made of cardboard, plastic or foam—but dense-pack would crush it.

materials deliveredI ordered up a few bundles of 1×2’s and a stack of fiberboard from the lumberyard and had on hand a case of low-VOC caulk (ChemLink NovaLink 35) from Green Building Supply. We air-stapled the 1×2’s to the sides of the top truss chord, fitted in rips of fiberboard, then went back to caulk the gaps and tape the seams. This left us with a 3 inch deep continuous chute separating the roof from the insulation. Any warm, moist air that migrates through will be whisked away, through soffit vents we’ll install in a few weeks.

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Fiberboard is an old-school building material and nowadays, a special order. It’s used for wall and roof sheathing, for insulation (R-2.5 per inch) and for sound-proofing. It’s classified as non-hazardous and is recyclable if you can find a facility. It’s made from recycled wood fibers, wax, and usually has a black asphalt coating on one side. It’s vapor-open and sturdy. I could have used OSB (oriented strand board) for slightly less cost and but greater environmental impact. We found the fiberboard easy to work with and not too dusty.

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We did a pretty good job with waste, although there were the inevitable cut-offs and caulk tubes that had to be landfilled.

wood scraps scrap rips

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