Roof vents

Published on April 15th, 2014 | by Henri

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Improving ventilation when re-roofing

Q.    In reading over your articles, you seem to be opposed to any kind of attic fan or roof venting fan as costly and ineffective for cooling off the rooms below.

Our roof’s shingles are over 20 years old and it would seem an opportune time to have an attic fan mounted that vents through the roof. If you feel this is an ineffective and costly solution, what do you recommend at this time since we’re considering having our shingles redone to help cool off the rooms below?

A.    Research has demonstrated that attic fans are seldom getting the replacement air they need from the attic itself. So they draw air from the conditioned living areas, robbing heated air from the house in winter and air-conditioned air in summer. That is why they are not considered the best way to go.

The best attic venting system is one consisting of continuous soffit vents (not a few holes here and there) and a continuous (also called “running”) externally baffled ridge vent. There must also be an uninterrupted air space a minimum of 1-1/2 inches above the insulation between the soffits and the ridge. Be sure that the selected ridge vent is externally baffled, such as Shinglevent II; unfortunately, most ridge-venting systems sold are not. With an externally baffled ridge vent, the wind is deflected over the vent. The result is an internal suction of the attic’s air through the soffit and the ridge vents, thus increasing its effectiveness — the Bernoulli Principle.

Venting drawing againNon-externally baffled ridge vents are ineffective in windy conditions, as the wind stops the exhausting of air through the ridge vent, which effectively stops the intake from the soffit vents — and they can get clogged with snow or admit it and rain.

The best way to increase the comfort in the bedrooms below the attic is to increase the level of insulation in the attic; it helps as much in summer as it does in winter. An additional way is to have light colored shingles installed.

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