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Basics of Roofing Ventilation

Although often overlooked, proper ventilation in your attic is essential to proper performance of any asphalt shingle roofing system. Popper ventilation can also decrease your monthly utility bills and even increase the comfort of your home. Perhaps the most common misconception about attic space is that you want your attic to be at the same temperature as your home. In fact the goal of any insulation and ventilation attic system is to have the temperature of the attic match the temperature outdoors. In the winter having your attic be too warm can lead directly to ice damming and cause water damage to your home. Conversely if your attic is cooler than the outside air that temperature differential can lead to condensation on the underside of your roof decking and cause

Pod vents/ Turtle vents

Pod vents are probably the most common form of ventilation on asphalt shingle roofs. They consist of square holes on the roof decking covered by metal or PVC perforated guards. If you bother to look up in your neighborhood you’ll likely see this form of ventilation dotting the roofs of the homes around you. They function as attic exhaust when there is adequate soffit ventilation to act as intake. They are ubiquitous because they work pretty well and are the least expensive form of attic ventilation. The downside is that they can still create hot-spots in your shingles leading to premature decay of the asphalt. In certain wind conditions can also act as intakes, sucking rain directly into your attic.

Gable vents

Probably the second most common for of ventilation. Gable vents are installed into the wall of the home at the peak of the roof. This type of passive ventilation does have a large area, but is less effective at ventilating the whole attic space because it’s not well set up to use convection but rather relies on ordinary air motion to ventilate the attic. This system can again cause hot-spots on your asphalt shingles and should not be used in combination with any ventilation system other than soffit vents. Like pod vents under certain wind conditions can cause ventilation that should function as an exhaust to instead become an intake and suck water into your home. When we are replacing roofs, it’s quite common for us to board up the inside of gable vents to allow the systems that we install to operate correctly.

Turbine vents, Whirleybirds

Turbine vents or “whirleybirds” as they are referred to in the industry are an effective form of passive ventilation that relies on convection in your attic. As warm aipasses over the fans as it rises it spins the turbine making a low pressure zone causing the whirleybird to spin faster. Although they are not the most attractive ventilation option they are about 40% more effective at circulating air in an attic than a typical box vent. Whirleybirds can be particularly useful on homes with little or no ridge lines.

Power Turbines

These function much like a whirleybird, except that they have a small electric motor powering the fan continuously or only when your attic reaches a certain temperature. Power turbines are overkill in most residential applications, but can still be useful if you have a very large attic space and little to no ridgeline.

Ridge vents

Ridge vents are the gold standard for passive ventilation in asphalt roofing systems assuming that you have a long enough ridge line on your home. The ridge vent is installed by cutting a gap along the whole ridge of your roof and covering it with a specialized ridge shingle that allows air to pass though. In combination with adequate soffit ventilation this causes continuous air flow from the soffit of your home straight along the underside of the decking. Because there is even ventilation on both sides of the ridge, varying pressure zones get equalized and it’s very unlikely to turn into an intake. The completely even distribution of exhaust at the highest point of the roof also avoids hot-spots in your attic, potentially prolonging the lifespan of asphalt shingles and, combined with sufficient insulation, can also decrease your energy bills.