What is ridge ventilation, and how does it work?
Short answer. Ridge ventilation is exhaust at the roof peak that works together with intake at the eaves: warm air rises and escapes along the ridge, pulling outside air in through the soffits and up along the underside of the roof deck. Wind blowing over the ridge adds suction, so the system works on hot still days and windy ones.
The two forces at work
- Stack effect: warm air is lighter than cool air, so attic air rises toward the peak and leaves through the highest opening. The greater the height between the soffit vents and the ridge, the stronger the draw.
- Wind effect: wind moving over the roof creates low pressure over the ridge and on the downwind side. A baffled ridge vent is shaped so wind from either side deflects up and over it, adding suction instead of blowing in.
What the airflow does
Air enters each rafter bay at the soffit, runs up under the deck along the baffle, and exits at the ridge. In a Georgia summer, that washes heat off the underside of the deck. In winter, it carries off moisture that drifts up from the house before it condenses on the cold deck. Because the opening is continuous, every bay gets airflow, not just the bays near a few vents.
Its limits
- It needs intake. Without soffit or edge intake, a ridge vent pulls from the house or from itself.
- It needs a ridge. Hip roofs with very short ridges may not have enough length.
- Box vents, gable vents or a power fan on the same attic short-circuit it.
- It cannot remove moisture faster than a bath fan dumping into the attic adds it.
- Cathedral ceilings need a clear vent channel from eave to ridge for it to do anything.
Compare it with the alternatives in ridge vent vs box vents and see how it fits the whole system in roof ventilation basics.