What Is a Ridge Vent?

A ridge vent works by convection. The installer cuts a narrow slot in the deck on both sides of the peak, sets a baffled vent product over it, and covers the vent with ridge cap shingles. Warm air gathers at the top of the attic and leaves through the slot, while cooler outside air is drawn in through intake vents low on the roof, usually in the soffit. The pair is what makes the system work. Building codes set a minimum amount of net free vent area relative to attic floor area, and the vent’s rated airflow is what gets counted against it.

The question homeowners actually ask is about attic heat, upstairs rooms that never cool, and sometimes mold or ice dams. On a reroof, ridge vent is a linear-foot line on the estimate, and the first thing to find out is what intake the attic has. Swapping box vents for a continuous ridge is a common upgrade pitch, and some shingle manufacturers tie warranty terms to adequate ventilation, so it is worth reading what the shingle line says.

Mixing exhaust types is the classic mistake. A ridge vent working alongside box vents or a powered fan lets the attic pull air from the nearby exhaust instead of the soffits, which short-circuits the airflow. Old vents have to be sealed up when a ridge is added. A ridge vent over blocked or missing intake does little, and on a short hip-roof ridge there may not be enough length to do the job alone.