How Many Soffit Vents Do I Need for My Attic?
Vent your condensation frustrations by installing these necessary air outlets
Highlights
Soffit vents rely on air rising.
Their purpose is to flush old air out of an attic.
Checking soffit vents often is important to keep out pests.
A good ratio is 1.2 vents for every 150 square feet of attic space.
Chances are you’ve seen thousands of soffit vents in your life but just didn’t know what they were. They are designed to blend into the roofline and gutters of a house so well that you might not know they’re even there unless you know what to look for. These vents—designed to move air throughout the attic—cover one square foot. That means that on a 1,700-square-foot house, you’ll need between 13 and 15 soffit vents.
How Does a Soffit Vent Work?
A professional roofer near you should install a soffit vent in the area that connects the edge of your roof to the underside of the roof eaves. A soffit vent then relies on air movement to flush stagnant air inside an attic. Air rises through the vent outside the attic, pushing the old air through alternate vents. These passive airflow vents help keep the attic cool in the summer, reducing air conditioning bills. In the winter, the effect is felt less as you lose some hot air, but proper ventilation is even more important in the winter when condensation is more likely.
Types of Soffit Vents
A soffit vent is an attic vent, not a roof vent. That means there is limited space to install a soffit vent, which is why they’re often placed on the horizontal area underneath where the roof extends beyond the home's wall.
Single
Single soffit vents are the most commonly seen soffit vents, and with good reason. It used to be much less expensive to simply cut out a space for the vent and install it. Now, with more modern building materials, many homeowners opt for continuous soffit vents, which wrap around the entire home.
Continuous
Continuous soffit vents are rising in popularity due to their efficacy—they work better than single vents—and their style. Continuous vents run the entire length of the roofline where the attic is, so they blend in much better with the rest of the home. They’re hard to notice unless you're directly underneath them.
How Many Soffit Vents Do I Need?
| Attic Square Footage | Square Footage of Ventilation Required | Vents Required |
|---|---|---|
| 800 | 5.35 | 7 |
| 1,200 | 8 | 10 |
| 1,500 | 10 | 12 |
| 1,800 | 12 | 15 |
| 2,200 | 14.66 | 17 |
| 2,800 | 18.66 | 22 |
The amount of ventilation your attic needs depends mostly on the size of your attic. There’s an excellent rule for determining the required number of soffit vents. Every 150 square feet of attic space needs 1 square foot of ventilation. Since a soffit vent is just under 1 square foot, you can divide the square footage of your attic by 150, then add 2 (since you can’t have too many vents).
The height of your attic doesn’t factor into the calculation, as once air enters the attic, it’s usually enough to disturb and shuffle the existing air around. The reason you need more vents than you may think is that air doesn’t always rise at the same rate throughout your house. Any side with consistent wind will see movement. For this reason, soffit vents are spread evenly around your attic’s perimeter.
Common Soffit Vent Problems
Pest Infestation
This is the biggest problem with soffit vents. In the summer, cool air falls from soffit vents and attracts pests trying to stay cool. In the winter, the opposite happens, and the comfortable warm air can be a magnet for unwanted invaders. Soffit vents often have a tight mesh installed that helps prevent critters from entering, but persistent pests can easily chew through them. Check your soffit vents at least once a season to prevent an infestation.
Blocked Ventilation
Soffit vents don’t really collect leaves or other debris as they’re under the house, but they can still get clogged from years of dust buildup. Another common cause of a blockage is if the vent is flush with the floor inside an attic and you accidentally kick or knock something in front of the vent.
Frequently Asked Questions
One of the disadvantages of soffit vents is they can bleed warm air from the attic during winter, resulting in slightly higher energy bills and a colder house. There are ways to mitigate this effect—mostly just closing the vent in the fall. What’s most important is your attic is ventilated to some degree in the winter.
The short answer is no, you can’t install too many soffit vents. The air is cleaner and there is a nice breeze when the house is properly ventilated. This same practice applies to soffit vents, and it’s much better to overventilate than to have air sit in the attic without movement.
When comparing soffit vents and fascia vents, the difference lies in their air channeling. Soffit vents depend on air rising into the vent and therefore the attic, while fascia vents rely on wind to blow air in. Fascia vents are often simpler to install and appear as a gap between the roof and the soffit.
The best way to ventilate an attic will depend on your individual space, but it’s usually a combination of different vent types. Soffit vents, fascia vents, and roof vents should be enough for almost every space. If that isn’t working, consider adding a fan or two inside the attic to keep the air moving.