How Much Ventilation Will You Need for Your Space?

Selecting the correct amount and type of roof vents for your home can be based on a number of different factors. Things to consider are climate zone, length of ridge, open or vaulted attic spaces to name a few.


So how do you know how to get the perfect number of vents to have your home breathing right?

Here’s our guide on calculating the correct amount of ventilation for your home. You can also use the calculator on our website to calculate your ventilation requirements.

Calculating area of house


What to know before starting – mixing ventilation

We do not recommend mixing different types of ventilation on the same attic space. Choose a single type of ventilation and apply the correct amount evenly on the same side of the ridge. You want to have a balanced system of intake air from the soffit and exhaust air through the roof vents.

Steps to calculate the appropriate amount of ventilation needed in your home

  1. Calculate the square footage of your attic space. To do this, measure the length and width of your home. 
  2. For example:

    Width: 40 ft, Length: 30 ft (40ft x 30 ft = 1200 sq. ft.)

  3. Find the amount of ventilation needed for intake and exhaust. According to the National Building Code, you need 1 sq. ft. of ventilation for every 300 sq. ft. of attic space. Divide your square footage by 300 sq. ft., then round up to make sure you’re getting enough ventilation. 
  4. 1200 sq. ft./300 sq. ft.= 4 sq. ft. of required ventilation (Intake and Exhaust)

  5. Convert square feet of Net Free Area (NFA) to square inches. Multiply square feet of NFA by 144. 
  6. 4.00 sq. ft. x 144 = 576 square inches of NFA needed

  7. Calculate the optimal amount of ventilation required. To ensure your roof vents are drawing from your soffits and not your other roof vents, we recommend that 50% of your ventilation should be provided by your soffits, and 50% should be provided by your roof vents (50/50). This means you should divide this number by two.
  8. 576 sq. in. /2= 288 sq. in. of ventilation is required on the roof

  9. Determine the number of vents required. The number of vents required for your home depends on the vent selected.
  10. For example, if you are choosing a 50 square inch roof vent, 6 vents are required for a 1200 sq. ft. application:

    288 square inches divided by 50= 5.76 vents ~6 vents (rounded up)

It is important to note that if your roof pitch is less than 4/12 or you have a vaulted or cathedral ceiling you will have to double the amount of ventilation needed.

Duraflo® offers a range of ventilation products in varied sizes, styles and heights. Check out your options here.

Share on:

Newest Posts

Sign Up to our Newsletter

Trade resources, industry news, product updates and more.

Can’t find what you need?

We’re here to help! Drop us a message and we’ll do our best to get you the answer or information you need.