Improving Attic Ventilation
Installing soffit vents is step one in increasing the level of ventilation in your attic
For most of us, the attic is a place to store clothes, luggage and old family photos, but for energy researchers it's a hot topic of discussion. In the last several decades, building codes have called for increased attic insulation. Most experts contend that a well-ventilated attic keeps the house more comfortable in summer and guards against moist, heated air building up in winter. There are also dissenting voices who say that the benefits of ventilation are overrated.
Who's right? Obviously more research is needed, but here's what we do know:
- Don't avoid ventilating your attic for fear you're letting cold air into the house. Your actual living space is sealed and insulated at the attic floor—the attic is outside this envelope.
- If there are asphalt shingles on your roof, the attic must be ventilated to comply with the terms of the manufacturer's warranty.
- One reason for the lack of agreement over attic ventilation is the tremendous variation in climate across North America. Rarely will you find a building practice that works everywhere.
For instance, attic ventilation is used widely in cold climates to evacuate the warm, moist air that escapes from the living space below. If this air lingers, it can condense on the underside of the roof sheathing and rot it. A healthy airflow also helps with ice dams, which begin to form when warm air in the attic melts the snow from beneath and creates runoff that refreezes on the colder eave. Great, but neither of these problems is experienced in warmer climates.
Our suggestion? If your home is fitted solely with small gable-end vents or a ventilator high in the roof, you might want to consider adding soffit vents to increase airflow. These vents allow outside air to enter the attic at the lowest point of the roof—along the underside of the eave. They're most effective when used in conjunction with a continuous ridge vent.
What to look for
Soffit vents come in several sizes and styles, including small round discs and rectangular grilles. We opted for aluminum strip vents that measure 3 in. wide x 8 ft. long. This style vent provides a quick way to ventilate every rafter bay. Strips vents come in white, brown and silver; you'll pay less than $3 for an 8-ft. length.
Mark two parallel lines
Start by using a chalk reel to snap two parallel lines down the center of the soffit. Space the lines 2 in. apart; that will allow the vent to overlap the cutout by ½ in. on each edge.