Do I need soffit vents if I have gable vents?
Short answer. Gable vents can ventilate an attic on their own through cross flow, but adding soffit vents improves airflow along the underside of the roof, especially near the eaves. If the house has or is getting a ridge vent, the usual recommendation is soffit intake with ridge exhaust and the gable vents closed off from inside.
Three common setups
- Gable vents only: wind blows through one gable and out the other. It moves air through the middle of the attic but leaves the lower roof deck near the eaves stagnant. Common on older Georgia homes and houses without overhangs.
- Soffit plus gable vents: cooler air enters at the eaves and warm air rises out the gables. Better than gables alone, though the gables sit lower than a ridge, so the exhaust pull is weaker.
- Soffit plus ridge vent: the setup most shingle manufacturers prefer. Air enters along every eave and leaves along the peak, washing the whole underside of the deck.
Why gables and ridge vents clash
A gable vent sits close to the ridge. When both are open, the ridge vent draws air in through the nearby gable instead of from the soffits, so airflow short-circuits across the top of the attic and the lower deck gets little. That is why roofers usually cover gable vents from inside when a ridge vent goes in, leaving the louvers outside for appearance.
What to do on your house
Look at the eaves first. If you have overhangs, adding soffit vents is usually worth it, with baffles at the top of each wall so insulation cannot block them. If the house has no overhang, intake vents installed along the roof's lower edge are an option. Size the intake to at least match the exhaust. For the full comparison see ridge vent vs box vents and roof ventilation basics.