Know Your Roof · Attic Ventilation
Roof Ventilation and Ridge Vents: How Your Attic Breathes
Quick answer
A ridge vent is the exhaust vent along the peak of the roof. Air comes in low at the soffit, rises as it warms, and leaves through the ridge vent, so it only works if air can get in at the bottom. Together, the two carry heat and moisture out of the attic.
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What roof ventilation does
Attic ventilation moves outside air through the attic to carry off heat and moisture. In summer, that keeps the attic from baking the shingles from below. In winter, it keeps the roof deck cold and dry, which helps prevent ice dams and condensation.
How a ridge vent works
A ridge vent runs along the peak, under a row of ridge cap shingles, over a slot cut in the roof deck. Warm air rises to the highest point of the attic and escapes through it. Intake vents low on the roof, usually in the soffit, let fresh air in to replace it.
Balanced intake and exhaust
Ventilation works when intake and exhaust roughly match. A ridge vent can't pull air through the attic if the soffit vents are blocked or missing. Mixing exhaust types on one roof, like a ridge vent with box vents or a power attic vent, can short-circuit the airflow, with one exhaust vent pulling air in through another.
Other exhaust vents
Box vents are low, hooded vents with no moving parts. Turbine vents spin in the wind to pull air out. Power attic vents use a fan. Gable vents sit in the end walls. A ridge vent runs the length of the peak, is hard to see from the ground and has no moving parts.
Signs your attic ventilation isn't working
An attic that feels very hot in summer. Frost on nails or on the underside of the deck in winter. Mold or dark staining on rafters. Ice dams. Shingles curling or aging early. Soffit vents covered by insulation.
Looking for another word? See the roofing terms glossary, A to Z.