How Much Ventilation Does Your Attic Actually Need?

Jenna Jonaitis
Written by Jenna Jonaitis
Updated November 15, 2021
Bright attic bedroom with sofa and bed
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  • Your attic needs 1 square foot of ventilation per 300 square feet of attic space.

  • Your ventilation should be split equally between intake and exhaust vents.

  • Poor ventilation leads to roof damage, higher energy bills, and reduced air quality.

  • Determine if your attic is properly ventilated using 7 simple tests.

  • Improve your attic ventilation by adding roof and soffit vents, installing fans, and ensuring your vents aren’t dirty or blocked. 

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The attic is often one of the most overlooked spaces in the home. But proper ventilation improves energy efficiency, increases your roof’s lifespan, and reduces the chance of water damage. Learn exactly how much ventilation your space needs and how to know if you have enough already. We also cover ways to increase your intake and exhaust ventilation.

How Much Ventilation Does Your Attic Need?

Your attic needs at least 1 square foot of ventilation for every 300 square feet of attic space. That means the typical ratio of attic area to attic ventilation is 300-to-1. Half of your ventilation should be exhaust vents, and half should be intake vents.

To determine the square feet of your attic, multiply the length by the width. For example, if your attic is 30 feet by 50 feet, it has an area of 1,500 square feet. Divide that number by 300. For a 1,500-square foot attic, that means you need 5 feet of ventilation. Half of those feet (2 1/2) should be intake vents, and the other 2 1/2 feet should be exhaust vents.

Your vent may have a label noting the square feet, or you can measure the opening yourself. But if the vent has grates, subtract the grates from the vent size. The vent openings are what count toward the ventilation square footage. Any air resistance or interference, such as grates, doesn't count.

7 Ways to Help Determine If Your Attic Has Enough Ventilation

You have a few options for checking to see if your attic has enough ventilation. These simple tests can give you big answers about your attic—and ultimately, your home.

1. Check Out Your Roof and Eaves

If you have few or no vents in the eaves or on the roof, it’s time to add some. Roof vents vary. Some are ridge vents, and others are gable vents. Talk with a local roofer to determine what’s right for your home.

2. Touch Your Ceiling on a Hot Summer Day

If your ceiling is hot to the touch, your attic is too warm and not getting enough airflow. Your energy bills are probably higher than they need to be because your AC is working overtime. Plus, your shingles are likely getting hot and could deteriorate your roof.

3. Look for Ice on Your Eaves in the Winter

If there are icicles or thick ridges of ice on your eaves, your attic doesn't have enough ventilation. Warm air is getting trapped in your attic. So when the snow melts, the water refreezes on the eaves and creates ice dams.

4. Perform a Smoke Test

Complete a smoke test using incense, a match, and a flashlight on a non-windy day, so you know how air typically travels. Watch how the smoke travels in and out of your attic to get a good idea of the ventilation.

5. Watch for Frost and Dampness in the Winter

If you notice frost or dampness in your attic during the winter, it’s a sign that warm air is exiting the rooms in your home. The moisture is condensing on your roof sheathing or rafters.

6. Note Temperature Differences Between Rooms

Is there a room in your home that always feels cooler or hotter than the others? Poor attic ventilation might be the culprit. You may also want to contact a local insulation contractor who can check to see if your home could benefit from more insulation.

7. Your Air Conditioner Is Working in Overdrive

If you don’t have proper ventilation, your AC might be working extra hard to keep your house cool. If your AC unit seems to be running all the time or is breaking down more often, it could be a sign you need more attic ventilation.

Why Attic Ventilation Is Critical

Attic ventilation helps your home perform at optimal efficiency. Here are some of the major benefits of proper attic ventilation:

  • Helps prolong the life of your roof

  • Prevents ice dams, interior leaking, and roof damage

  • Helps keep your home temperature more comfortable

  • Reduces energy bills

  • Reduces chance of mildew, rusty nails, wood rot, and deterioration in the attic

  • Prevents shingles from scorching in the summer and deteriorating the roof

  • Helps maintain roof warranties (improper ventilation can void them)

How to Improve Ventilation

Increasing the ventilation in your attic has huge payoffs. While you can add vents and fans yourself, be aware of safety concerns. Working on tall ladders can be dangerous, and exposing yourself to insulation can cause health issues. That’s why we recommend working with a local roofing company who can handle tricky aspects of the work. Some houses are more challenging to ventilate properly than others, which is another reason to get a pro for the job.

No matter who tackles the work, here are the easiest ways to improve your ventilation.

Insert Roof Vents

Typically placed on a roof’s peak, roof vents and exhaust vents help ensure warm, moist air can flow outside. Depending on your home, you may need ridge vents, roof turbines, or another type of exhaust event. Ridge vents run the length of your attic, while turbines sit at the top of your roof and use the wind to pull hot air out of the attic.

Install Intake Vents

Insert intake vents above your eaves, also known as soffit vents. Soffit vents allow for air from the outside to enter your attic. They work in correlation with roof vents for proper airflow.

Consider Gable Vents

Detail of a gable roof vent
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Beyond roof and soffit vents, your house may need extra airflow. A contractor can place these at the gable ends of your roof to help drive air out of the attic.

Install Fans

Attics typically ventilate well on their own naturally. But if you live in a hot or humid climate, you may need fans to aid in the ventilation process. Fans can help draw air out of your attic. You can have a thermostat activate the fans when the attic is too warm or choose a manual model. Attic fan installation costs $370 to $880 on average.

Ensure Vents and Fans Aren’t Blocked or Dirty

Dirt, insulation, and your belongings can all get in the way of attic airflow. While you can store boxes and items in your attic, be sure they don't block your vents or fans. If they’re dirty, clean them to allow for the greatest airflow.

Contact a Roofing Professional

A roofing pro can assess your home and determine what ventilation solutions your space needs. A roofing professional usually charges $45 to $75 per hour to install roof and gable vents, but they can save you thousands in lower energy bills and roof longevity.

Can You Have Too Much Attic Ventilation?

Yes, you can have too much exhaust ventilation in your attic, which can deteriorate your roof and raise your energy bills. When too much air circulates in your attic, your roof collects moisture—leading to damages and leaking.

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