How Much Ventilation Does Your Attic Need?
Poor attic ventilation can push your energy bills through the roof
Highlights
An attic needs one square foot of ventilation per 300 square feet of attic space.
Ventilation should be split equally between intake and exhaust vents.
Poor ventilation leads to roof damage, higher energy bills, and reduced air quality.
You can determine if your attic is properly ventilated using some simple tests.
Improve ventilation by adding vents, ensuring they’re not blocks, and installing fans.
The attic is often one of the most overlooked spaces in a home. This is unfortunate, since 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 will also cover ways to increase your intake and exhaust ventilation.
How to Calculate How Many Roof Vents You Need
To calculate how many roof vents you need, you must know the attic’s square footage. This enables you to determine how many exhaust and intake vents you need. Next, you must convert the measurement into square inches to determine the exact amount of ventilation required.
Here’s a quick sample calculation:
([Attic square footage/300]/2) x 144 = Total number of square inches of ventilation required per exhaust and intake
| Attic Square Footage | Square Inches of Ventilation Required per Exhaust and Intake |
|---|---|
| 1000 | 240 |
| 2000 | 480 |
| 3000 | 720 |
How Much Ventilation Does Your Attic Need?
An attic needs at least one square foot of ventilation for every 300 square feet of attic space. That means the typical ratio of attic area to attic ventilation is 300:1. Half of your ventilation should be exhaust vents and half should be intake vents.
To determine the square footage of your attic, multiply the length by the width. For example, if your attic is 30 feet by 50 feet, it has a total area of 1500 square feet. Divide that number by 300. For a 1500-square-foot attic, that means you need five square feet (or 720 square inches) of ventilation in total. Half of that (350 square inches) should be intake vents, and the other half should be exhaust vents.
Your vent may have a label noting the square footage, 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, does not count.
7 Ways to Help Determine If Your Attic Has Enough Ventilation
There are 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 is time to add some. Roof vents vary. Some are ridge vents and others are gable vents. Talk with a local roofer to determine what is 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 compromise your roof.
3. Look for Ice on Your Eaves in the Winter
If there are icicles or thick ridges of ice on your eaves, the attic does not 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 is a sign that warm air is exiting the rooms in your home. The moisture is condensing on the 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 lack 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.
Do You Need Attic Ventilation?
Yes, you definitely need attic ventilation. Attic ventilation is crucial to lengthen your roof’s lifespan and to reduce wear and tear on your HVAC system. Given the high HVAC and roof replacement cost, attic ventilation can help you save money.
A lack of ventilation in the summer can cause excessive heat inside a home, damaging a roof’s adhesive and causing shingles to curl. In the winter, trapped heat and moisture can cause the roof’s decking to swell, leading to premature roof deterioration and necessary replacement.
Here are some specific ways attic ventilation helps your home:
Can 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 causing roof to deteriorate
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 is 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 to 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 roof, while turbines sit at the top of a 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
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. 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. Find an attic fan installer near you to ensure the job is done right.
Ensure Vents and Fans Are Not 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 do not block vents or fans. If they are dirty, clean them to allow for the greatest airflow.
When to Contact a Roofing Professional
A roofing professional can measure your attic and determine how much ventilation your attic requires. Not only will you have an accurate measurement of what is needed to keep your attic properly ventilated, but you will know that the vents are properly installed and functioning well.
It is especially important to contact a roofing professional if you notice interior leaking, damaged roofing materials, or ice dams. It is also a good idea if you notice your energy bills are higher than normal or you suspect mold growth in the attic.
Can You Have Too Much Attic Ventilation?
Yes, you can have too much exhaust ventilation in your attic, which can cause your roof to degrade prematurely and increase your heating and cooling bills. You may also run into pressure issues when ventilation is unbalanced. If there is too much intake and insufficient exhaust, the attic becomes uncomfortable, shingle integrity can be compromised, and the warranty may be voided. If you have too much exhaust and not enough intake, the attic will depressurize and pull air from your home into the attic, which increases energy costs (and may cause problems with moisture and ice dams).