What Is a Ridge Vent?

What a ridge vent is

A ridge vent is a long strip that sits over the peak of the roof. Under it, the roofer cuts a narrow gap in the roof deck along the ridge.

The vent covers that gap, keeps rain and bugs out, and lets air pass out through small openings along its sides.

On most shingle roofs the vent is then covered with cap shingles, so from the street it looks like a slightly raised ridge line.

It is one type of exhaust vent. Exhaust vents are the high openings that let air out. They work with intake vents, the low openings that let air in.

Our roof ventilation guide covers the whole system and the code math. This page is about the ridge vent itself: how it is rated, the main types, how it is installed, and the mistakes that stop it working.

How a ridge vent moves air

Warm air rises. In an attic, the warmest and dampest air collects right under the peak. A ridge vent gives that air a way out at the highest point, along the whole length of the roof.

As it leaves, cooler outside air is drawn in through the intake vents near the eaves. The result is a steady flow from low to high under the whole roof deck.

Wind helps too. When wind blows across the ridge, it creates lower pressure on the sheltered side of the vent, which pulls more air out.

Some vents add a baffle, a small raised lip along the outer edge, to shape that wind flow. A plain gap with no baffle can let wind push straight into the vent instead.

The key point is that a ridge vent cannot pull more air out than the intake lets in.

The shingle makers' association says intake should supply 50 to 60 percent of the open venting area and exhaust 40 to 50 percent, so intake always matches or beats exhaust ⁴.

A long ridge vent over a house with blocked or missing soffit vents is mostly decoration.

Types of ridge vents

Ridge vents differ in what they are made of, what covers them, and how they handle wind and weather. Read the maker's data sheet for the exact rating; the figures below are from the product sheets we read.

Ratings differ between models from the same maker. One evaluation report lists an 18 sq in per foot model and two narrower models at 16 sq in per foot ³.

Baffled vs unbaffled ridge vents

Worked example: how much ridge vent an attic needs

Take a 1,500-square-foot attic under a simple gable roof. The ridge is 40 feet long. The code's base rule is 1/150 of the vented area ¹. Using a vent rated at 18 sq in per linear foot ³:

Here the ridge comes up just short, so the plan either adds intake, uses the 1/300 rule if its conditions are met, or accepts a small shortfall in exhaust while keeping intake larger. Illustrative house. Run your own numbers in our attic vent sizing tool.

Where a ridge vent works, and where it does not

A ridge vent works best on a gable roof with a long, level ridge and a vented attic below it. The longer the ridge, the more exhaust it can give. Hip roofs have short ridges, so a ridge vent alone may not reach the area needed; some makers sell hip-ridge vents for that case.

It does not belong over a sealed, unvented attic, where insulation sits right under the roof deck by design. It also needs open air under the ridge. A vaulted ceiling with no air channel between rafters, or a ridge blocked by framing, leaves nothing for the vent to draw from.

Roof slope matters. One evaluation report limits its vents to slopes between 3 in 12 and 16 in 12, or 3 in 12 and 12 in 12 for narrower models ³. A very flat or very steep roof may need another product.

Benefits of a ridge vent

• It vents along the whole length of the ridge, the highest and warmest part of the attic.
• It is low and covered with cap shingles, so it blends into the roof line.
• It has no motor and no moving parts.
• It needs few holes in the field of the roof, unlike rows of box vents.
• Paired with continuous soffit vents, it can wash air evenly under the whole deck ⁸.

Limits of a ridge vent

• It is only as good as the intake below it.
• A short ridge, as on many hip roofs, may not give enough length.
• It cannot be added where the ridge is blocked by framing or where the attic is sealed by design.
• Very fine filters can clog with dust or pollen over time.
• It needs a careful slot cut and correct nailing, so it is a job for a roofer, not a weekend project.

What drives the cost of a ridge vent

We do not publish dollar prices for this item. These are the things that move the price on a quote:

• Length of ridge to be vented, measured in linear feet.
• Whether it goes in during a full reroof or as a separate job, which means removing and replacing cap shingles.
• Vent type: plain shingle-over, filtered, baffled, or exposed metal.
• Whether the deck slot already exists or must be cut.
• Removing old box vents or turbines and patching those holes.
• Adding or opening soffit intake to balance the new exhaust.
• Roof height, pitch and access, which affect labor and safety setup.

How a roofer installs a ridge vent

This is what you should see happen. It is not a do-it-yourself guide: ridge work is high and steep, and a licensed roofer with fall protection does it. The steps follow one evaluated product's instructions ³; always follow the maker's own sheet.

1. The roofer measures the attic and checks there is enough intake to match.
2. Old exhaust vents in the field of the roof, such as box vents or turbines, are removed and the holes are decked and shingled over.
3. A slot is cut along the ridge. For one product it is ¾ inch on each side of a ridge board, or 1½ inches centered where there is no ridge board ³.
4. The last 6 inches of deck inside the outside wall line at each end are left uncut ³.
5. The vent sections are centered over the slot and butted end to end, with no gaps. In cold weather that maker recommends a ⅛-inch gap between sections for expansion ³.
6. The vent is nailed through its pre-drilled holes with long roofing nails, and cap shingles are nailed over it, six nails per cap shingle on that product ³.

Why a wider slot does not help

It is tempting to think a wider cut lets more air out. It does not. The air still has to pass through the vent's own openings, and the net free area is set by those openings.

One vent maker says plainly that a wider slot will not add net free area, and that a slot cut too wide can put the opening too close to the vent's edges and let weather in ⁵.

So the slot width on the maker's sheet is not a minimum to beat. It is the size the rating was built around. Ask your roofer which product they are using and what slot width its instructions call for.

Keeping a ridge vent working

• From the attic on a bright day, look up at the ridge. You should see light or feel air along the slot.
• Check that soffit vents are open and not painted over or buried in insulation.
• After a big storm, look from the ground for cap shingles that have lifted or blown off the ridge.
• Watch for stains on the ridge board or rafters, a sign of weather getting in.
• Do not add a power fan or new box vents later without asking how they will interact with the ridge vent.

What goes wrong with ridge vents

• Mixed exhaust: a ridge vent plus box vents, a turbine, gable vents or a power fan over one attic. Air flows by the shortest path between them, so one exhaust can act as intake and pull weather in ^{6 4}.
• A power fan pulling air in through the ridge vent from outside. One trade article reports a case where this clogged the ridge vent ⁹.
• No intake. The vent has little to draw from, and the attic stays hot and damp.
• Slot not cut, or cut too short. The vent is on the roof but sits over solid deck.
• Slot cut too wide, putting the gap close to the vent's open edges ⁵.
• Snow or wind-driven rain entering an unbaffled or unfiltered vent.

Why you should not mix exhaust vents

Each kind of exhaust vent works in its own way. A power fan uses a motor. A turbine spins in the wind. A ridge vent relies on rising heat and wind pressure across the peak.

Put two kinds over the same open attic and the stronger one can draw air in through the weaker one, instead of from the soffits ⁹.

The Asphalt Roofing Manufacturers Association warns that combining different exhaust vents on the same roof over a common attic can short-circuit the system ⁴.

A large vent maker goes further and says it is never OK to mix two different types of attic exhaust vents ⁶.

When a ridge vent goes in, the old box vents and turbines usually come out.

Weather and snow filtration

A ridge vent is an opening at the most exposed spot on the roof, so keeping weather out is part of the design. Makers use three main tools: baffles that turn the wind, filters that catch blown rain and snow, and narrow openings.

One maker says its vent uses outer and inner baffles to prevent wind-driven rain and snow from getting in, with vent holes only ⅛ inch wide ⁷. Another vent is built with a nonwoven fiberglass weather filter ³.

No vent is perfect in every storm. Fine powder snow can blow through many vents in a hard wind. If you live where that happens often, ask your roofer which ridge vents they have seen hold up locally, and check the attic after the first big storm.

Code rules that apply to ridge vents

The International Residential Code does not name ridge vents. It sets how much vent area an attic needs and where it goes, and a ridge vent is one way to supply the top part.

This is model code. States and cities adopt and amend it on their own schedule, so confirm the edition with your building department.

Ridge vent compared with other exhaust vents

Common misconceptions

Myth More exhaust is always better.

Reality Exhaust without matching intake does little, and intake should be equal or larger ⁴.

Myth A wider slot gives more airflow.

Reality Net free area is set by the vent's openings, not the slot ⁵.

Myth Adding a power fan helps a ridge vent.

Reality Mixing exhaust types can short-circuit the attic ⁶.

Myth Every ridge vent is rated the same.

Reality Ratings vary by model; one report lists 18 and 16 sq in per foot models ³.

Myth A ridge vent fixes ice dams on its own.

Reality Ice dams also depend on insulation and air sealing below the roof.

Local rules and climate

Whether your attic needs 1/150 or can use 1/300 depends on your climate zone and on vent placement, under the code your jurisdiction adopted ¹. Some states and cities run older editions or add amendments. Your building department can tell you which applies.

Climate also shapes the product choice. In snowy places, filtered and baffled vents matter more.

In high-wind areas, ask whether the vent has a wind rating; one evaluation report limits certain uses to set design wind speeds and roof heights ³.

We do not list local adoption here because it changes; ask the department or your roofer.

When a ridge vent matters, and what to ask

A ridge vent is worth a close look when you are reroofing, when the attic is hot or damp, or when you see frost or mold on the underside of the deck. Ask your roofer:

• Which ridge vent product will you use, and what is its net free area per foot?
• How many linear feet of ridge can be vented after the uncut ends?
• How much intake do I have now, and will you add or open soffit vents to match?
• Will you remove my box vents, turbines or gable vents, and patch them?
• Is the vent baffled or filtered for snow and wind-driven rain?

Keep going

• Ventilation calculatorWork out intake and exhaust for your attic
• Roof replacementThe best time to add a ridge vent
• Roof inspectionCheck vents, intake and attic moisture
• Asphalt shinglesThe roof most shingle-over vents are made for

Related terms

Roof Ventilation

Roof ventilation is the system of vents that lets outside air enter an attic low, near the eaves, and leave high, near the ridge, so heat and moisture do not build up under the roof deck.

Soffit Vent

A soffit vent is an opening in the underside of a roof's overhang, the soffit, that lets outside air flow into the attic so it can sweep up under the roof deck and leave through exhaust vents near the peak.

Intake Vent

Any vent low on the roof, usually in the soffit or at the eave, that lets outside air into the attic.

Asphalt Shingles

Asphalt shingles are roofing pieces made from a fiberglass mat coated with asphalt and topped with mineral granules, laid in overlapping rows so water runs off the roof.

Roof Sheathing

Roof sheathing is the layer of plywood, OSB or wood boards nailed across the rafters or trusses.

Reroofing

Reroofing is the work of putting a new roof covering on a house that already has one, either by tearing the old covering off down to the deck (a replacement) or by laying the new covering over the old one (a recover, often called an overlay).

Roof Underlayment

Roof underlayment is a sheet laid over the whole roof deck before the shingles or other roof covering go on.

Also referenced from: Ridge Cap, Roof Ventilation, Soffit Vent, Roof Wind Uplift