How Many Roof Vents Do I Need?

two roof vents that are side-by-side

A roof vent is a type of fixture installed on your roof that exhausts hot air. The size of your roof and attic space will determine how many roof vents you need. Luckily, there is a basic formula you can use to determine this. Read on to learn which kinds of vents will work best for your roof and how many vents you will need to install one of these systems.

Roof Vent Types

Ridge Vents

Ridge vents run along the apex of your roof and are long and narrow.

Gable Vents

Gable vents, as the name suggests, attach to the gables rather than the roof itself and go through the siding. They come in a number of shapes, such as squares, rectangles, and triangles.

Soffit Vents

Soffit vents, or under-eave vents, are installed on the underside of the roof that hangs over the siding — the eaves.

Other Vents

There are also box- or dome-shaped vents that go through the roof itself. There are also gable and roof fans, which actively pull the hot air out of the attic.

Fan Calculation

As a general rule, your roof needs 1 square foot of vent area for every 150 square feet of attic space. Thus, if your attic is 450 square feet, you need roof vents equaling 3 square feet. They should be divided equally between inlet and outlet vents, and they can be used in any combination that will work with your roof's design.