What does a proper roof ridge vent detail look like?
The slot
The opening in the decking is what actually vents the attic. On most homes the cut leaves a gap of roughly an inch on each side of the peak; where a ridge board runs under the peak, manufacturers typically call for a wider cut so air can get around the board. The slot normally stops several inches short of each gable end and is left closed at chimneys, walls, and anywhere the space below is separate, such as a vaulted ceiling or a garage firewall. Follow the vent maker's sheet, because cut widths differ between products.
The vent and cap
- Shingle-over vents are rolled out or laid in sections centered on the slot and butted tightly at the joints.
- Ridge caps go over the vent with nails long enough to get through the vent and into the decking, often 1 3/4 inches or longer, placed on the nail lines marked on the vent.
- Ends get the plugs or closed end pieces the product provides so wind-driven rain and insects cannot enter from the side.
- An external baffle, the raised lip along the outer edge of better vents, helps wind pull air out instead of pushing rain in.
The parts people forget
A ridge vent needs intake. Without soffit or edge vents it draws air from the house through ceiling gaps, or pulls outside air backward through its own openings. Other exhaust on the same attic, such as box vents or a gable louver, should normally be closed so the ridge pulls from the eaves rather than from a nearby shortcut. The 1/300 ventilation rule and the balanced split are covered in roof ventilation basics, and the comparison with static vents is in ridge vent vs box vents.