How Many Soffit Vents Do I Need?

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How many soffit vents do I need and what is considered a waste of money? This is your guide to determining how many soffit vents you should have.

3 min read

What Are Soffit Vents and Do I Need Them?

Soffit vents are the vents in the underside of your roof overhang. They allow for air to flow from within your attic to outside and vice versa. Having the correct amount of vents can give you several benefits.

  • Extend the life of your roof
  • Reduce energy costs
  • Prevent ice dams
  • Prevent mold growth
  • Keep your roof cooler

As you can see, having vents that increase the airflow through your attic is a must.

How Many Soffit Vents Do I Need?

You could start by asking your contractor, as they should have the answer to this question. But it's also smart to educate yourself so that you can hold your contractor accountable.

Local Building Code

Your first step is to check the local building code. You may find that there are regulations about how many you should have. If your local building code dictates this, then you need to follow these guidelines.

The General Rule

The general industry rule is that you should have one square foot of venting space for every 150 square feet of attic area. About half of the vent space should be on the bottom of your roof in the soffit. The other half should be at the top of your roof in the gable or ridge.

This encourages a circular motion of airflow through the space.

Do Your Own Calculations

Start by multiplying the length and width of your attic. Now you have your attic's square footage. Divide this number by 150. Now you have the total amount of venting square footage needed.

(length x width) ÷ 150 = sq. ft. vent area needed

Your next step is to divide your total area of venting needed by two. This resulting number will tell you how much soffit venting area you need.

sq. ft. vent area needed ÷ 2 = soffit vent sq. ft. needed

You'll need to look for the "net free area" listed by your vent's manufacturer. This is the actual opening square footage and not the dimension of the entire vent.

Calculate how many vents you need based on the measurement of this open space when compared to your total soffit vent space needed. Keep in mind that different soffit vent types have different open spaces, so you'll need the exact measurement for the vent you intend to use.

Check Your Roofing Soffit Today

Now that you're no longer asking how many soffit vents do I need, it's time to take a look at your roof. Walk outside and look up at your soffit. Check for vents and count how many you have. You can perform your own square footage calculations, or have a roofing professional come out and do the calculations for you.

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