Attic Ventilation: A Guide For Homeowners

Attic ventilation is an important component in keeping your home’s air flowing and keeping the interior temperature balanced. A properly ventilated attic can save you money on energy bills and can help avoid moisture damage.

In this guide, we’ll look at what exactly attic ventilation is, and how to tell if you need more ventilation in your home attic. We’ll look at how to calculate how much ventilation you need. We’ll also look at different kinds of vents and answer some common questions.

What Is Attic Ventilation?

Attic ventilation balances the flow of air in your home and reduces moisture in your attic. This is accomplished with intake vents that take in the air and exhaust vents that push out the air.

In the summer, the sun heats up the roof, which heats up the air in your attic. This hot air gets pushed down into your house, raising the temperature. Because hot air is also full of moisture, this means your attic is also now full of moisture, which can cause mold to grow and condensation to damage your attic materials. Proper ventilation ensures the moisture is moved out of the attic space and that the temperature can be more regulated without running your air conditioning system to the max or running up your energy bills.

In the winter, proper attic ventilation can keep the moisture from that hot air from damaging the attic and roof. Proper ventilation is also key in preventing ice dams, which occur when snow melts on the roof and then re-freezes on the eaves and in gutters. These dams can grow so large that water can’t run off the roof, and instead it goes underneath the shingles, damaging them and the roof.

Keep in mind that attic ventilation is different from attic insulation. Insulation helps maintain the temperature of your attic, while ventilation keeps the air moving. They work together to make your attic’s atmosphere consistent!

How To Tell If You Need More Attic Ventilation

How can you tell if your attic needs more ventilation? Look for these signs:

• Look at the roof to see if any vents are installed.
• Pay attention in winter for ice dams forming.
• Use your hand to see if the attic ceiling is hot.
• Look for moisture or mold on the attic’s materials.
• Keep an eye on your HVAC system – if your air conditioning breaks down, it could be a sign that it’s working overtime to cool down your house.

How To Calculate Your Attic Ventilation Needs

Generally, you’ll want one square foot of ventilation for every 300 square feet of attic space. This number is called net-free area, or NFA. Use this number to calculate the number of vents you need. Your vents should be divided equally between intake vents and exhaust vents.

Let’s walk through how to calculate this, with example numbers:

• First, measure the length of your attic, and then the width.
  • Ex: 50 feet long, 40 feet wide
• Multiply the two numbers to get the attic’s area in square feet.
  • Ex: 50 x 40 = 2,000 square feet
• Then, divide that number by 300. This gives you the NFA in square feet.
  • Ex: 2,000 ÷ 300 = 6.67 square feet
• Since most vents are NFA rated in square inches, you’ll convert the NFA by multiplying it by 144, the number of square inches in a square foot.
  • Ex: 6.67 x 144 = 960.48 square inches
• Finally, divide this number by two to calculate the coverage you’ll need by the two types of vents.
  • Ex: 960.48 ÷ 2 = 480.24 square inches covered by each type of vent.
• Once you’ve selected the type of vent you want, divide that number by the NFA rating of your vent.
  • Ex: You choose an 18-square-inch exhaust vent. 480.24 ÷ 18 = 26.68, meaning you’ll need 27 of these exhaust vents.

Roof Intake Vents

Let’s look at a quick overview of the most common types of intake vents. These pull in the air from outside.

Gable Vents

These vents are usually found on homes with one long roof ridge. These vents are placed on either end of the roof, under the peak. Gable vents are passive ventilators, meaning they act in much the same way that an open window does. Depending on which way the wind is blowing, they can act as exhaust vents, too.

Shingle-Over Vents

Shingle-over vents are used in homes with little or no roof overhang, and are designed to be covered with shingles, to camouflage them on the roof. They are often installed at the roof’s edge or on the peak, or ridge, of the roof.

Roof Edge Vents

The areas where your roof overhangs the house are called the eaves, or soffits, and it’s where you’ll find roof edge vents, also known as soffit vents. These intake vents are lower than exhaust vents because the cooler air they pull in will force the hot air out of the exhaust vents.

Exhaust Vents

Let’s take a quick look at the most common types of exhaust vents. These vents push interior air outside.

Powered Exhaust Vents

These vents operate much like a fan in a window does. They are typically electrically powered fans that pull stale air up and out through the exhaust vent. They’re effective, but they do raise your energy costs. You can also install more energy-efficient solar-powered or wind turbine exhaust vents (like the one pictured) to help keep that cost down.

Ridge Vents

A ridge vent is one long continuous vent at the very peak of your roof. It’s the most common type of exhaust vent, and it’s extremely effective. Because there’s so much surface area, they let a good amount of hot air out, and their position at the roof’s peak means they let out the hottest air.

Static Vents

Static vents operate much like powered vents, but don’t require electricity. Instead, they use vertical ventilation (where the cold air pulled in by the intake vents pushes the hot air out). They’re generally installed near the peak of the roof, where the hottest air is.

Attic Ventilation FAQs

What is the best way to ventilate an attic?

While having an equal number of intake and exhaust vents, and calculating if you have enough ventilation, is a huge step in making sure your home is ventilated properly, vertical ventilation is the best way to efficiently vent your attic. This harnesses the power of gravity, by having intake vents installed near the bottom of the roof, and exhaust vents near the peak. Cold air comes in and forces the hot air out. Science!

What happens if an attic isn’t vented? 

Attics that aren’t vented can have all kinds of issues, including trapped moisture, which leads to mold, mildew and wood rot. In the winter, this can also lead to ice dams forming.

Do attic vents work?

Yes! Moving the stale air out of your attic is essential to maintaining a healthy environment in your home. Having both intake vents and exhaust vents prevents that air from standing in your attic.

How can I tell if my attic is properly vented?

You can do a visual check – make sure the vents on your roof aren’t blocked by trees or clogged with debris, and in winter, check for ice dams. You can also check when you’re inside by feeling the ceiling underneath the attic. If it’s hot, your attic might need more ventilation.

Should I install vents myself or hire a professional?

While vents aren’t wildly difficult to install, it’s probably best left to a roofing professional. They’ll be able to recommend which vent types are best for your roof, and can make sure they’re installed properly with no leaks!

The Bottom Line

Attic ventilation is essential to the health of your home and the quality of your air. There are many kinds of vents to ensure your house is ventilated properly, and a roofing professional can help you decide which ones to choose. Attic ventilation is usually affordable compared to other home projects, but if improving ventilation is part of a larger home renovation effort, you might consider getting a cash-out refinance.