What is a ridge vent?
Updated August 2026
A ridge vent is a continuous exhaust vent running the length of the roof peak, hidden under cap shingles, that lets hot and humid attic air escape. It only works as half of a pair. Soffit vents under the eaves admit cool outside air at the bottom, that air warms and rises, and the ridge vent releases it at the top, so the attic quietly exchanges its air all day with no fan and no power. Roofers size the pair by the 1:300 rule: 1 square foot of net free vent area per 300 square feet of attic floor, split about evenly between intake and exhaust.
Where it is
From the yard, a roof with a ridge vent looks like the peak is an inch or two thicker than the shingle field, with a faint shadow line running its whole length. Installers cut a 1 to 1-1/2 inch slot on each side of the ridge board, cap it with a baffled plastic or metal vent, and shingle over the top. The confirmation is inside: on a bright day, an unlit attic shows a thin ribbon of daylight along the peak. While you are up there, check the other half of the system. Look down the rafter bays toward the eaves and make sure blown insulation has not buried the soffit openings, and that rafter baffles hold a 1–2 inch air channel above the insulation.
What it does
Ventilation does two jobs in opposite seasons. In summer it dumps heat, since an unvented attic can push past 150 degrees on a 95-degree day, cooking shingles from below and pouring heat into the rooms underneath. In winter it removes the moisture that rises from showers, cooking, and laundry, which otherwise condenses on cold sheathing and shows up as frost on the roofing nails, then as black mold on the north slope, then as delaminated plywood. Trapped attic heat also melts the snowpack, which refreezes at the cold eave and builds ice dams. Blocked ventilation shortens shingle life by years, and most manufacturers make code-compliant ventilation a condition of the warranty. The classic tell of a dead ridge vent is a second floor that stays 8–10 degrees hotter than the first all summer.
Maintenance
Two checks keep it honest. From the ground each spring and fall, scan the ridge for lifted cap shingles or crushed sections; once a year, on a sunny day, confirm the daylight line from inside the attic. The ridge vent inspection guide covers both. The item to verify after any re-roof: some crews install the vent over solid decking and never cut the slot, so the roof looks vented and breathes nothing. Two rules follow. Never pair a ridge vent with a powered attic fan or open gable vents on the same attic, because the exhaust short-circuits and pulls air from the nearest hole instead of the soffits. And when airflow is poor, add intake, not more exhaust; continuous soffit venting runs $500–1,200.
What it costs to replace
A replacement ridge vent runs $8–15 per linear foot, or $300–650 to retrofit a typical 40-foot ridge.
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Frequently asked questions
Ridge vent or powered attic fan: which is better?
A balanced ridge and soffit system wins for most houses. It has no motor, no wiring, and nothing to fail, and it ventilates continuously rather than only above a thermostat setpoint. A powered fan at $300–600 installed can depressurize the attic enough to pull conditioned air out of the house through ceiling gaps, and in a worst case it can backdraft an atmospherically vented water heater. If you install one anyway, make sure intake venting is generous first.
Do I still need soffit vents if I have a ridge vent?
Yes, and this is the most common ventilation mistake in older houses. Without intake at the eaves, the ridge vent pulls its makeup air from wherever it can, which means recessed lights, the attic hatch, and bath fan gaps, dragging heated indoor air and its moisture up into the attic. Aim for at least as much net free intake area as exhaust. Adding continuous soffit vents or retrofitting round plug vents runs $500–1,200.
Can rain or snow blow in through a ridge vent?
A modern externally baffled vent deflects wind up and over the opening, so rain rarely enters. Failures trace back to cheap unbaffled vents, a slot cut wider than the vent covers, or missing end plugs. Wind-driven snow is the harder case, since fine powder can sift through any exhaust vent in blizzard conditions. Find a small drift under the ridge each winter and the answer is a vent with an internal weather filter, not a blocked one.
How do I know if my ridge vent is blocked?
Go into the attic at midday with the lights off. A working vent shows a continuous line of daylight at the peak; patchy or absent light means paint, debris, a wasp nest, or an uncut slot. Back that up with the physical signs: frosted nail tips in winter, insulation matted flat near the eaves, and an attic that bakes on a mild day. A roofer's inspection runs $150–300.