Do I need gable vents if I have a ridge vent, or a ridge vent if I have gable vents?
Short answer. You do not need both. In an attic with soffit intake and a ridge vent, gable vents are usually closed off because they can short circuit the airflow, letting air enter at one end and leave at the ridge without sweeping the lower attic. Gable vents alone can be acceptable when there is no soffit intake, but they make a less effective system.
How each system moves air
- Soffit and ridge: air enters low along the eaves and exits high along the peak, washing the underside of the whole roof deck.
- Gable vents: openings at each end wall. Wind pushes air in one end and out the other, so they act as both intake and exhaust depending on wind direction. They mostly ventilate the upper middle of the attic.
Why combining them backfires
A ridge vent depends on air entering low. With gable vents open, the ridge vent can pull air from the gable openings instead, because they are closer and larger. The eaves, where moisture and heat often collect along the decking, get less flow. Many ridge vent manufacturers recommend closing gable vents when a ridge vent is installed with soffit intake.
How to close them
Leave the exterior louvers in place for appearance and block them from inside with rigid foam or plywood, sealed at the edges. If they are purely decorative, nothing needs to change.
When gable vents should stay
- The attic has no soffit intake and adding it is not practical. In that case, gable vents may be the whole system, and a ridge vent should not be added without intake.
- A section of attic is cut off from the main ridge, such as over a garage with a separate roof line.
Whatever you choose, size the system to code and use one exhaust approach per attic space. More in roof ventilation basics and ridge vent vs box vents.