Ask the Architect

Yes, roofs need venting

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Q. We need a new roof. I’ve always been told that roofs need vents. Ours has a ridge vent. Every time we have severe wind and rain, it leaks. I’ve been told it’s not steep enough. There are so many types of roof vents — fans (I’ve been told they’re a big cause of fires), ridge vents, the windows. Do roofs need to be vented, and what, in your opinion, is the best type?

A. Thank goodness for technology! And thank you for your return address. I was able to look at your roof from a satellite on the computer, and verify that you have an adequate attic area for venting. All roofs need to breathe, thus venting is necessary.

Without venting, many problems arise, such as heating up of the interior space through the attic floor by radiation. The heat given off by the attic can increase your air conditioning bills substantially and make you uncomfortable while trying to get a good night’s rest. The roof shingles above the attic begin to fry, like bacon strips, sizzling not only from the sun but the heat radiating upward. The wood roof structure collects humidity and becomes steamy, bowing if it’s under-sized, causing a rippling effect in the roof rafters that tears shingles down the middle after just a few years, in some cases. You could only see this if you got up close, like a roofer does, but you’ll feel the effects if a leak occurs. So, yes, you need venting.

The formula for venting is 1 square foot for 150 square feet of attic area, which means that just a ridge vent isn’t enough for most roofs. We calculate for something called “free area,” which means the little chambers or vent louvers have to be deducted, a common mistake that people make when figuring out required vent area. Depending on the type of vent louvers, the deduction of free area can be 15 to 20 percent.

Think of it as being like when you have a cold and your breathing passages are partially blocked. You work harder to breathe. So does your home. Ventilation fans reduce the need for larger vent openings by moving air mechanically, but do not eliminate the need for adequate cross-venting, or the fan will have to work harder and can wear out much more quickly. I like a vent fan, located at or near the center of the roof, with end vents at all end points of the roof. The further the air can move, the more heat it takes with it. Reflective roofing and insulation between the rafters will also reduce heating of the attic. Roof shingles do reflect heat, so ask about them or research the internet. They don’t need to be a light color to be reflective. Make sure that 3 feet of membrane covers the perimeter, including the ridge, ends and bottom edge just above the gutter. This is code required.

© 2016 Monte Leeper. Readers are encouraged to send questions to yourhousedr@aol.com, with “Herald question” in the subject line, or to Herald Homes, 2 Endo Blvd., Garden City, NY 11530, Attn: Monte Leeper, architect.