2 minute read
Why Proper Attic Ventilation Is So Important
by Expert Contributor Kevin O’Donnell, Owner of O’Donnell Roofing Co.
When performing the initial inspection at a residential building, a professional roofing contractor will almost immediately begin analyzing the existing roof ventilation design. These tell-tale signs of poor attic ventilation are often found during the initial site visit: soft or delaminating plywood, mold, musty odor, and rust on the nails seen on the underside of the deck. When one or more of these conditions is present, it is time to improve. Let’s start at the beginning.
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. Up until the 1950s, 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 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.
Soffit vents
During the construction boom of the 1950s, asphalt shingles and plywood were installed regularly, with minimal attic ventilation. Homes were still being built without overhangs (soffits). It took almost 30 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.
Ridge vents
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. 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 those warm vapors hit the cold underside of the plywood (cold due to, for example, snow on the roof), the effect of condensation will occur and can cause catastrophic water damage and mold. This is similar to a cold glass of iced tea in the summer: The condensation forms 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.
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.
Kevin O'Donnell, Expert Contributor and Owner of O'Donnell Roofing Co.
O'DONNELL ROOFING CO. -- Since 1924
4th Generation Owned and Operated • Residential & Commercial Roofing • Windows, Skylights, Siding, Gutters • Historic Restoration • Metal Roof Specialist • Solar Installation • Senior Citizen Discount
610-449-8188
www.ODonnellRoofingCo.com
