How much should ridge cap overlap?
Short answer. For shingle ridge cap, overlap is set by the product's exposure, the visible part of each piece, which is printed in its installation instructions; cut three-tab pieces are commonly laid at about 5 inches of exposure, and thicker manufactured ridge caps often specify more. For metal ridge cap, laps are set by the panel manufacturer, commonly in the range of about 4 to 6 inches, with sealant or butyl tape in the lap.
Shingle ridge cap
- Exposure, not overlap, is the spec. Each piece covers the nails of the one before it. If the exposure is 5 inches on a 12-inch piece, the overlap is about 7 inches.
- Nail placement. Nails go in the spot the manufacturer marks, usually just above the exposed area and covered by the next piece. Exposed nails on a ridge are a common leak point.
- Direction. Start at the end of the ridge away from the prevailing wind, so each lap faces downwind and wind does not drive rain under the edges. On hips, start at the bottom and work up.
- Weather. Ridge caps applied in cold weather can crack when bent; manufacturers often recommend warming them first.
- Ridge vents. On a vented ridge, caps go over the vent using longer nails as the vent maker specifies.
Metal ridge cap
- Lap pieces by the amount in the panel manufacturer's details, commonly about 4 to 6 inches.
- Seal laps with butyl tape or approved sealant.
- Lap away from prevailing wind.
- Use foam or vented closures under the cap as specified to keep out wind-driven rain and insects.
- Fasten with the specified screws into the panel ribs or structure, not randomly.
Why the details matter
Ridges take the strongest wind and full sun. Short laps, wrong direction and exposed fasteners are typical causes of ridge leaks and blow-offs after Georgia thunderstorms. Using the manufacturer's matching ridge cap also matters for wind warranty coverage on many shingle lines. See ridge vent vs box vents and wind damage to roofs in Georgia.