- Q.Wouldn't a single-sided ridge vent
be more effective than a standard ridge vent for a home built
on a windy site? It seems that with openings on both sides of
the ridge, a standard vent would simply short-circuit when the
wind blows rather than draw air from the eaves
A.Paul Fisette, director of Building
Materials and Wood Technology at the University of
Massachusetts Amherst, responds: In order for a ridge vent
to exhaust, you need a pathway and a reliable driving force.
Both a single-sided and a double-sided ridge vent provide a
pathway, so the important question is this: What is the main
driving force that pushes attic air up and out of the ridge
While wind direction can induce roof venting — and it's
been shown that even soffit-only venting can draw air out of
roofs — most often the answer is the buoyancy of the
attic air. If there is a fair amount of heat loss from the
house into the attic, then the buoyancy of the warm air rising
causes it to escape at the highest point, the ridge.
However, a more energy-efficient house experiences less heat
loss, so in that case buoyancy becomes less of a driving force.
Based on some tests I've run, I think it's important to install
ridge vents that have an external baffle, like ShingleVent II
(Air Vent Inc., 800/247-8368, www.airvent.com). As wind passes over the
roof ridge, the airstream jumps over the vent's baffle, causing
suction as the air lifts upward — the same way an
airplane wing works (see illustration). Called the Bernoulli
effect, this driving exhaust force works regardless of wind
direction. Without an external baffle, either a single- or a
double-sided roof vent can allow outside air to come in and
short-circuit the venting process.