Replacing an Unvented Low-Slope Roof
Hello GBA Community-
I have a mid-century ranch house with a Japanese-inspired roof. It is long and relatively low-sloped 4/12 (?) with deep eaves and hip ends with large slated vented gables; there are no soffit vents. The prevailing winds are the same orientation as the gable vents. We are in the DC suburbs mixed-humid weather (climate zone 4A) with lots of rain storms, and every few years some large snow storms. The roof on the northern side keeps its snow without melting and no icicles and the southern side melts completely dry from the sun almost immediately. Summer is hot and humid.
We have two quotes for a new roof — one with a rigid Cor-A-Vent that slips under the shingles with a continuous cut in the plywood sheathing to provide venting to the attic, and the other replaces as-is with no soffit vents.
16+ years ago, a new roof was installed with a ridge vent and the former owners blew in a good amount of cellulose insulation into the attic. When we purchased the house in 2008, the first thing we did, which now seems regrettable after reading Lstiburek’s Rules for Venting Roofs, was to install recessed lights absolutely everywhere – kitchen, dining room, living room, hallway, bathrooms, bedrooms, and art lighting – which are all on the main level directly below the attic. There are metal boxes to separate the lights from the cellulose insulation, but our electrician said they were probably not air-tight.
Here are a few other considerations:
* It seems excessively hot in the attic in summer (but it’s DC – I’ve not taken a temp).
* Most of the plywood will need to be replaced as it is soft/spongy and from the outside, you can see the outlines of the roof trusses under the shingles.
* There are no visible leaks inside or evidence of any leaking.
* The soffits and the T1-11 siding is redwood plywood. A vinyl or plastic continuous soffit would not look good. In surveying the neighborhood with these similar style houses, there are no soffit vents.
Thanks for your patience through the long question…
Any advice on what to do?
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