How wide is a ridge vent?
Vent width vs cap width
The vent has to be covered by the cap shingles, with the caps' edges lapping a little past the vent onto the field shingles. That is why many vent lines come in two widths: a narrower version for 10 inch caps and a wider one for 12 inch caps. Pairing a wide vent with narrow caps leaves vent edges exposed to sun and rain; pairing a narrow vent with wide caps can leave the caps unsupported at the edges.
Typical numbers
- Rigid shingle-over vents: commonly in the 9 to 14 inch range, in 4 foot lengths.
- Rolled vents: similar widths, cut from the roll to length.
- Aluminum ridge vents: the older exposed metal style, with their own widths and no cap shingles on top.
The slot is a different number
- Truss roofs: about 1 inch on each side of the peak, for roughly 2 inches total, is a common manufacturer spec.
- Roofs with a ridge board: about 1 inch beyond each face of the board, with a maximum total opening set by the manufacturer.
The vent's width gives it room for nailing zones on both sides of the slot, where nails go into solid deck.
Why it matters to you
When cap shingles look too narrow for the vent, or vent edges are visible from the street, the pairing may be wrong. Exposed vent material weathers and can let wind under the caps. Ask your roofer which cap width the vent was designed for. See architectural vs 3-tab shingles and ridge vent vs box vents.