Our homes need to breathe, and that includes your attic. Soffit vents are found below the eaves of your roof, to allow fresh air from outside to flow into your attic and replace the air there.
The process of exchanging attic air is called ventilation. In addition to soffit vents, your house also needs ridge at the top of the roof and/or gable vents near the peak of your roof on the gable ends. Soffits allow air to enter your attic … and the air leaves the attic through the vents above, either ridge or gable.
Benefits of Soffit Vents for Ventilation
Ventilation is key to increasing the life of your roof, because moisture trapped inside your attic may allow wood rot to begin. In the summer, you can save money on air conditioning while in the winter, soffit vents can help prevent ice dams.
Types of Soffit Vents
Soffit vents come in different colors to coordinate with the color of your roof, siding and exterior trim. They're made of aluminum, galvanized steel and some are made from plastic which I'm weary of because of my experience running a handyman business.
More important are the various shapes and sizes of vents. The continuous vents are the easiest to install as other shapes require the supporting plywood/OSB to be manually cut for the shape chosen. The shapes (you can find them at HomeDepot.com) include:
- Continuous soffits – run along the edge of your roof as shown in the photo above. However, if you look closely at the photo, you'll see that perforations in the material occur one out of every six sections.
- Rectangular soffits – are popular and using the calculation below, you can determine how many of these soffits need to be installed. Master Flow also has a soffit with a built-in screen that can be closed to prevent embers from getting into your attic when there's a wildfire threat.
- Round/circular soffit vents – are preferred by some for the look although they may take more work to install. Air Vent also offers these with/without screening.
Calculating The Amount of Soffit Vents Needed
You need some math to calculate the number of soffit vents needed to provide enough attic ventilation. When calculating the area of the vent, you should only count the actual open area versus the size of the vent.
Here are the numbers you need to calculate. For a more detailed description, check out TodaysHomeowner.com‘s article.
- Calculate the volume (cubic feet) of air in your attic.
- Divide the cubic feet by 150 square feet, to determine how much vent space your need.
- Divide the vent space by two, as you need equal vent capacity at the bottom of the attic (soffit vents) and near the roof (ridge and gable vents).