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Monday, May 30, 2016
Helping the hot air escape

Q. I have to re-roof, and I’m being told to put a vent in the top of my roof instead of an attic vent fan that sticks up. They described it like a slit under the top shingles that is more hidden than the fan cover sticking up above the roof. What do you think of their idea? Is it just as good or better?

A. Many years ago I made the mistake of following the latest fad in roofing. Ridge venting was touted as a great way to vent the roof, since heat rises and the vent is located under the top shingles. What the roofer does is cut the wood sheathing at the peak to leave a 2-inch-or-so-wide gap that air can escape from. Next they place a specially made honeycomb-like filter over the gap and then nail the shingles to it.

The problem with this method is that it doesn’t allow for enough air movement. Your roof and attic get choked with heat buildup, the shingles heat up like strips of bacon on a frying pan and little by little they become brittle in the middle. Sounds like a song, but you won’t be singing when you see the pieces of shingles come rolling off your roof. If you have any doubt about what I’m saying, you only have to see my backyard after any windstorm and to count the flakes of roofing coming off while I try to settle with my insurance company from the “superstorm.”

The insurance company will probably give you a hard time about how your shingles weren’t installed correctly, without telling you why they think that. The installation of the shingles has to follow manufacturer’s requirements, which include proper venting of your roof. Whoever told you that the little strip of venting at the top of your roof would somehow be enough hasn’t yet learned the hard way what heat buildup can do.


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Forgive me, after years of thermodynamics education I cannot help myself. Heat does not rise, hot air rises. Heat conducts and radiates, convection being the conduction of gas molecules gets its own category but it still is conduction on a mass scale.

I read your answer, and I am curious what you thoughts are for a hot unvented roof. With the addition of closed cell spray foam under the roof sheathing, bringing the attic into the conditioned space. Seems that major roof tile companies are on board and is allowed under new codes. A few studies show roof temps not grossly above traditional vented roofing systems.

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