Ridge vent vs off ridge vent: what is the difference?
Short answer. A ridge vent runs continuously along the peak, while an off-ridge vent is a short, low-profile rectangular vent, usually a few feet long, installed on the slope just below the ridge. Off-ridge vents are a fallback for roofs with too little usable ridge, such as hip roofs, and each unit provides less exhaust than a long ridge vent.
How off-ridge vents work
The vent sits over a rectangular opening cut in the deck, usually within a couple of feet of the peak, with shingles lapping over its upper flange. Because it is near the top of the attic, it works as high exhaust like a ridge vent, just over a shorter length.
Comparison
- Location: ridge vents sit on the peak; off-ridge vents sit slightly down the slope.
- Coverage: ridge vents span the attic; off-ridge vents serve the area around them.
- Appearance: both are low profile; off-ridge vents show as short dark rectangles near the top.
- Leak points: off-ridge vents sit in the path of water running down the slope, so the upper flashing has to be done right.
- Use case: off-ridge vents fit hips, short ridges and ridges over finished rooms.
Can they be combined?
Treat them like any two exhaust types: avoid combining them over the same open attic unless the vent manufacturer approves it, because one can short circuit the other. On a hip roof, off-ridge vents may be the exhaust while the short ridge stays unvented.
Sizing
Check each product's net free area. You will often need several off-ridge units to match what a long ridge vent provides. See ridge vent vs box vents and roof ventilation basics.