How long is a piece of ridge vent, and how many pieces do you need?
Short answer. Rigid shingle-over ridge vent usually comes in pieces about 4 feet long, rolled vent in rolls of roughly 20 feet or more, and old style aluminum ridge vent commonly in 10 foot sections. To count pieces, measure every ridge, divide by the piece length, and round up, then check the cap shingle bundle label for linear feet per bundle.
Piece lengths by type
- Rigid plastic vent: about 4 foot sections that connect end to end, with the end pieces fitted with plugs.
- Rolled vent: commonly 20 feet or more per roll, unrolled along the ridge and cut to length.
- Aluminum ridge vent: exposed metal vent often sold in 10 foot lengths with connectors and end caps.
- Metal roof ridge systems: sized to match the ridge cap pieces from the panel maker.
Counting what you need
- Measure each ridge separately, end to end. A hip roof may have one short main ridge; a cut up roof may have several.
- Divide each ridge length by the piece length and round up. A 38 foot ridge needs ten 4 foot sections, with the last one trimmed.
- Add the cap shingles: the bundle wrapper states how many linear feet it covers.
- Count end plugs, two per separate ridge run if they are sold separately.
- Get nails long enough for the vent and caps.
The length that matters for airflow
The piece length you buy and the open slot you cut are different numbers. The vent usually runs the full ridge for looks, while the slot stops short of the ends. Airflow comes from the open slot length times the vent's rating per foot, so a 38 foot ridge with 6 inch setbacks at each end has about 37 feet of working vent.