Most people have been taught that warmer air rises and escapes from the high vents, while cooler air enters in lower vents. Thermal buoyancy is a major cause of air leakage from the living space to the attic, but research at the BRC shows that wind is the major force driving air exchange between an attic and the outdoors.
“Our research shows that the role of thermal buoyancy in diluting attic air with outdoor air is negligible,” says Rose.
This requires rethinking about the design and location of attic vents. For example, some ridge vents may allow air to blow in one side and out the other, without drawing much air from the attic. Rose believes that ridge vents with baffles create better suction to draw air out.
**Rose considers soffit vents to be very important.
“If a roof had only one type of vent device, I would choose soffit vents,” he says, “because they work well as inlets and outlets.”**
There’s less problem with rain and snow getting in, because soffit vents point downward. To get maximum protection, locate soffit vents as far out from the wall as possible. If rain or snow blow into the soffit, it’s less likely to soak the insulation or drywall.
Soffit vents should always be installed whenever there are high vents. High vents, on ridges or gables, will pull air out of the attic. Without soffit vents, make-up air would be drawn through the ceiling, which increases heat loss and adds moisture to the attic.
Because of the importance of soffit vents, Rose believes that at least 50 percent of the vent area should be low on the roof.