Expert Contributor by Kevin O’Donnell O’Donnell Roofing Co.
Why Proper Attic Ventilation is so Important, and a History as to why Yours Could be Faulty When performing the initial inspection at a residential building, a professional roofing contractor will almost immediately begin analyzing the existing roof ventilation design. There are often tell-tale signs of poor attic ventilation found during the initial site visit, mainly soft or delaminating plywood, mold, musty odor, and rust on the nails seen on the underside of the deck. When one, or all, of these conditions are present, it is time to improve. Let’s start at the beginning
Ridge vents
Soffit vents
Throughout the evolution of the construction industry, there have been some missteps, specifically in regards to the interaction between roofing and attic ventilation. Up until the 1950’s, when self- sealing asphalt shingles and plywood became the norm for most residential roofs, the typical materials were slate, tile, and cedar shake…all of which were typically installed on actual wood boards, and all of which “self-ventilated” or were more “breathable”. The attic conditions under these roofs would perform, even with just a couple gable vents or windows on the exterior walls. There was never a real concern for condensation or mold. During the construction boom of the 50’s, asphalt shingles and plywood were installed regularly, with minimal attic ventilation. Homes were still being built without overhangs (soffits). It took almost thirty years for the current ventilation model to be implemented regularly, which primarily includes soffit vents (intake air), and ridge vents (exhaust vents). The basic idea with attic ventilation is to have the same amount of “intake” air from the outside, as the amount of “exhaust” air.
In modern construction, the intake air comes typically from a continuous slot or perforated soffits… essentially holes to allow air into the attic space from under the overhangs. The exhaust is typically achieved by adding a “ridge vent” — another continuous slot at the peak of your roof where the air leaves the attic space. Though attic ventilation is important in the summer, it is crucially important in the winter months when the heat is on. Heat will rise through the walls and ceiling, and make its way into the attic space. With that heat loss is also vapor loss. When these warm vapors hit the cold underside of the plywood (snow on the roof), the effect of condensation will occur and can cause catastrophic water damage and mold. I always compare it to a cold glass of iced tea in the summer… the condensation will form on the outside (warm side) of the glass. The only way to stop these vapors from condensing into a liquid, is to combat them with cool fresh air from the outside. With this information on proper attic ventilation, you can monitor your own and see if yours needs an upgrade. NS
4th Generation Owned & Operated
www.ODonnellRoofingCo.com 610-449-8188
Historic Restoration & Metal Roof Specialist Senior Citizen Discount Residential & Commercial Roofing Solar Installation Windows / Skylights / Siding / Gutters
“We’ve repaired and replaced so many roofs in Marple Newtown, I moved my young family here to be closer to my work and to get more involved in the community.” ~ Kevin O’Donnell, Roofing Expert & Owner
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Newtown Square Friends & Neighbors
November 2018
