2 minute read
The Crucial Importance of Proper Attic Ventilation
by Expert Contributor Kevin O’Donnell, Owner of O’Donnell Roofing Co.
Late summer or early fall is a good time for homeowners to check out their attic or have it inspected so any repairs can be done before winter, when ventilation is most important. The initial inspection of a residential building starts by analyzing the existing roof ventilation design. Tell-tale signs of poor attic ventilation are soft or delaminating plywood, mold, musty odor, and rust on the nails seen on the underside of the deck. When one or more of those conditions is present, ventilation improvements are warranted.
A History About Why Your Attic Ventilation Could Be Faulty
Throughout the evolution of the construction industry, there have been some missteps, specifically in regards to the interaction between roofing and attic ventilation. Until the 1950s, 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 those 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 1950s, self-sealing asphalt shingles and plywood were installed regularly on residential roofs, with minimal attic ventilation. Homes were still being built without overhangs (soffits). It took almost 30 years for the current ventilation model to be regularly implemented. The basic idea with proper attic ventilation is to make sure the amount of “intake” airflow is greater than or equal to the amount of “exhaust” airflow. This is accomplished primarily by soffit vents for intake air and ridge vents for exhaust air.
In modern construction, the intake air typically comes from a continuous slot or perforated soffits, essentially holes that 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.
Attic ventilation is important in the summer, but it is crucially important in the winter months when the heat is on. As heat rises through the walls and ceiling, it makes its way into the attic space. With that heat loss is also vapor loss. When those warm vapors hit the cold underside of the plywood (cold due to, for example, snow on the roof), condensation will occur, which can cause catastrophic water damage and mold. This is similar to when condensation forms in the summer on the outside (warm side) of a cold glass of iced tea. The only way to stop these vapors from condensing into a liquid in your attic is to combat them with cool fresh air from the outside.
This information will help you monitor your own attic for proper ventilation, and help you determine if an upgrade would be a good way to protect your investment in your home.
Expert Contributor Kevin O’Donnell, Owner of O’Donnell Roofing Co.
O'DONNELL ROOFING CO.
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