Ridge Vent

A ridge vent is an exhaust vent installed along the full length, or most of the length, of a roof ridge. The roof deck is cut back on each side of the ridge to form a continuous slot, and a vented cap is fixed over it. The cap is then covered with ridge shingles, ridge tiles or a metal ridge cap so the vent is nearly invisible from the ground.

How it works

Warm air rises to the top of the roof space by stack effect, and wind blowing across the ridge creates suction that helps draw air out. Paired with continuous intake at the eaves, a ridge vent produces an even flow of air under the whole deck. Because it sits at the highest point, it is well placed to meet the US code option that allows the total vent area to be reduced from 1/150 to 1/300 of the attic area when 40% to 50% of the ventilation is located within 3 ft (914 mm) of the ridge, with the balance at the eaves.

Types

• Shingle-over ridge vents: rigid plastic or rolled fibrous mat products covered with cap shingles, common on asphalt roofs in North America.
• Externally baffled vents: designed so wind passing over the ridge accelerates past the opening, increasing suction and resisting rain and snow entry.
• Metal ridge vents: formed metal caps with perforated closures for metal roofs.
• Dry ridge vent systems: in the UK, ventilated dry ridge systems fix ridge tiles mechanically while providing high-level ventilation, typically rated as an equivalent continuous slot (for example 5 mm).

Considerations

• Ridge vents need adequate intake; without eave vents, they can draw air from the house.
• Hip roofs have short ridges, so ridge vents alone may not provide enough exhaust; alternatives include hip vents or individual roof vents.
• Mixing a ridge vent with gable louvres or powered fans can short-circuit the airflow.
• Net free vent area ratings, given per linear foot or metre, are used to size the installation.