How to Calculate Attic Vent Area Needed When Adding Soffit Vents
By: Ben Erickson
Keeping your attic cooler in the summer can increase the life of the roof as well as saving money on your air conditioning bill. To effectively cool the attic, outside air needs to circulate through it. One solution is to use the natural circulation caused by hot air rising to bring fresh air into the attic through soffit vents under the eaves, then expel the hot air through ridge or gable vents near the peak of the roof.
The general rule of thumb on the amount of total attic vent space needed is to have at least one square foot of vent space for every 150 square feet of attic area. Ideally, half the vents should be located in the soffit at the bottom of the roof and half in gable or ridge vents near the top to allow for natural circulation of air through the attic.
To find out how many soffit vents you need to install:
- Determine the number of soffit vents needed: Divide the total soffit vent area by the area of each vent. [soffit vent area in sq. ft. ÷ individual vent area in sq. ft. = number of vents needed].
Example: 5 sq. ft. soffit vent area divided by 0.5 sq. ft. vent area equals 10 soffit vents needed.
Space the soffit vents evenly around the bottom of the low sides of your roof.
There are several different types of soffit vents available including continuous, circular, and perforated vents made for vinyl siding. We’ll discuss the easiest to install, standard 8″ x 16″ vents.
- Screw or nail the vent into place.
The fresh air the soffit vents draw in should be expelled near the peak of the attic through vents in the gables, ridge vents in the roof, wind turbines, or power vent fans.
- Attic Ventilation (article)
- Adding Soffit and Ridge Vents (video)
- How to Install Soffit Eave Vents (video)
- Which Way to Face Soffit Eave Vents? (article)