What does a ridge vent do?

A ridge vent lets hot, damp air leave your attic through a slot along the roof peak, while cooler outside air comes in at the eaves to replace it. Working as a pair, the intake and the exhaust keep the space under your roof closer to the outdoor temperature, which protects the roof deck, the insulation and the ceilings below.

How a ridge vent works

Warm air rises. In an attic that air carries heat in summer and household moisture in winter, from showers, cooking and laundry. A ridge vent is a continuous exhaust opening at the very top of the roof, covered by a vent product and capped with ridge shingles so rain does not get in. Because it sits at the highest point, the rising air has a clear way out.

An exhaust vent only works if air can get in. That intake is normally the soffit vents under the overhang. Most building codes require roof and soffit vents to exhaust humidity and moisture that could cause insulation or other building materials to deteriorate.^[1] Virginia Cooperative Extension says most homes should have a combination of a continuous ridge vent along the peak of the roof and continuous soffit vents at the eaves to provide the most effective ventilation.^[1]

How much vent area a house needs

Extension gives a general guide of approximately 1 ft2 of net vent opening for every 150 ft2 of ceiling or attic space, with some exceptions, so your local building code governs.^[1] Net vent opening means the open area air can actually pass through, not the size of the product. Extension adds that if individual vents are used instead of continuous ones, the vents should be divided equally between the ridge and soffits.^[1]

What a ridge vent does for you

It cools the roof deck. Heat and trapped moisture shorten the life of roofing and framing, and an attic that breathes is gentler on both.

It helps with ice dams. Snow melts on a roof that is warmed from below and refreezes at the eaves. The U.S. Department of Energy's Building America program says to vent the roof to keep the roof cool to minimize the snow melt that leads to ice dam formation.^[2] Ventilation is only half of the fix, though. The same source says the most important step is to seal all of the air leaks from the conditioned space into the attic space to keep warm air from entering the attic in the first place.^[2] See why ice dams form on a roof and how to prevent them.

It moves moisture out. That helps protect insulation and wood from damp, which is a common root of attic mold and rot.

Why a ridge vent may not be working

A ridge vent is only as good as the path of air leading to it.

• Blocked intake. Insulation pushed against the eaves can smother the soffit vents. The Building America guide says baffles and insulation dams should be installed to keep insulation out of the soffit vents and to direct cooling air flow from the soffit vents up along the underside of the roof deck to the ridge vents,^[2] and that an air gap of at least 2 inches should be provided between the top of the insulation and the underside of the roof deck.^[2]
• No intake at all. Some houses have a ridge vent and no soffit openings, or soffits painted or boxed shut. Air then has nowhere to come from.
• Moisture dumped into the attic. ENERGY STAR lists kitchen, bathroom or clothes dryer vents that exhaust moist air directly into the attic space instead of outdoors as a problem to correct.^[3] A ridge vent cannot keep up with that.
• Damage. A cracked, crushed or torn-off section, or a ridge cap that has lifted, can let in weather and pests.

Signs worth a look include frost on the underside of the deck in cold weather, stained or dark sheathing, and rust on nail points. ENERGY STAR also names wet or damp insulation, indicating a leaky roof,^[3] and moldy or rotted attic rafters or floor joists, indicating moisture problems,^[3] as conditions to have a professional deal with.

When to call a licensed pro

Inspecting, repairing or replacing a ridge vent means working on the roof ridge, which is a fall hazard, so leave it to a roofer. In Virginia, the Board for Contractors defines roofing contracting as the service that provides for the installation, repair, removal, or improvement of materials common to the industry that form a watertight, weather resistant surface for roofs and decks.^[4] In the Board's classes, Class C covers a single contract over $1,000 but less than $30,000, with higher classes above that,^[5] so check the licence on DPOR's lookup before you sign.

Ask the roofer to look at the attic as well as the roof. A good inspection covers the soffit intake, the insulation at the eaves and what the bath and kitchen fans vent into.

Next steps: read how much ridge vent repair costs in Virginia, see whether a new roof is the time to replace the vent, browse roofing repair answers or roofing repair services. To have licensed local roofers look at yours, describe the job once.