How Many Vents Does a Roof Need?

vent on a house roof

Roof vents are those boxes and turbines you see on top of houses but you probably don’t think much about, if you think of them at all. Although you may not pay much attention to roof vents, did you know that they are a crucial part of your roofing system? 

Roof vents cool down your attic space and prevent moisture buildup in your home by improving air circulation. To operate efficiently, a home needs the right amount of exhaust vents and intake vents. 

How many vents a roof needs depends on factors such as the size or shape of the roof. Here’s a guide to help you calculate how many vents you need for your home.

illustration of a turbine roof vent
Photo Credit: Juan Rodriguez

What Is a Roof Vent?

A roof vent is a device that allows air to pass in and out of your attic. This system pulls in cool air to freshen up the attic airflow. This keeps air circulation from getting stale or too hot. 

A ventilation system consists of two types of vents

  • Intake vents are placed near the bottom of the attic. They push fresh air into the attic.
  • Exhaust vents are located at the top of the roof, usually placed along the ridges of the roof. Exhaust vents expel stale air from the attic so that new, fresh air can come in through the intake vents. 

The different types of exhaust vents include:

  • Box vents
  • Cupola vents
  • Dormer vents
  • Gable vents
  • Power vents
  • Ridge vents
  • Solar vents
  • Turbine vents (also known as whirlybirds)

And the types of intake vents are:

  • Gable vents
  • Soffit vents

Good ventilation lowers the temperature of the attic. Without a roof vent system, your attic would get too hot during the summer and the heat would get trapped in your attic with nowhere to go. In wintertime, ventilation keeps the attic temperature cool, which reduces the chance of ice dams forming on your roof.

Proper ventilation protects the attic from water damage. Home activities such as washing dishes, doing laundry, showering, or cooking produce moisture that travels up and gets caught in the attic. Without a place to go, this moisture stays trapped in the attic space. A roof vent helps release this moisture.

How Does a Roof Vent Work?

vents on a roof
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A roof vent that requires a power source such as electricity or solar power to work is an active vent. Without a power source, active roof vents won’t work. 

Passive vents don’t require electricity to work. Instead, passive vents rely on wind to operate, as wind blows air in and out of passive vents.  

Active roof vents can come with a built-in thermostat, which monitors the temperature of the attic. When interior temperatures get too hot, the roof vent automatically turns on and circulates the air to cool down the attic.

Another handy tool roof vents are often equipped with is a humidistat, which regulates moisture levels in the attic so they don’t get too high. 

Hot air rises, which is why exhaust fans are placed near the top of the roof or along roof ridges, so that naturally rising hot air can easily escape back outside while cool air enters from the bottom of the roof. 

How Many Vents Does a Roof Need?

It’s important to install the right number of roof vents on top of your house. A roofing system needs to be balanced so that it will keep your house effectively ventilated.

If there is too little ventilation, your roof will have moisture and overheating problems. On the other hand, large drafts of air filtering through your attic also cause moisture buildup, leading to water damage in your attic. 

The general rule of thumb is that if your house has a vapor barrier and is insulated, it needs one roof vent  for every 300 square feet of attic floor space.

For uninsulated attics without a vapor barrier, the formula calculation should be one roof vent for every 150 square feet of attic flooring. 

To calculate how many vents your roof needs, follow these steps:

  1. Determine how many square feet your attic floor has. To calculate this, multiply the width of your attic by the length of your attic. 
  2. Then divide that number by 300 ft. (or 150 ft. if your roof doesn’t have a vapor barrier) to figure out how many roof vents you need. 
  3. Then divide that number by 2, since half of the vents should be intake vents and the other half should be exhaust vents. Dividing by 2 will tell you how many of each type of vent you need for your roof. 

When installed, the roof vents should be evenly spaced. Placement is key, and it does little good for your attic if all the roof vents are crowded together in the same spot. 

If you aren’t sure about the number of vents your roof needs, consult a local roofing contractor for help. 

How Do You Know If Your Roof Has Enough Vents?

Poor ventilation causes your attic to overheat or results in too much condensation buildup, but having too few roof vents isn’t the only concern. Homeowners should be wary of adding too many roof vents to their house, otherwise large drafts and excess air circulation might cause damage to their roof. 

If you notice these signs of poor ventilation in your home, you need to add more roof vents to your home:

  • Leaks
  • Water damage
  • Condensation in your attic
  • Frost in your attic
  • Mold, mildew, fungus, or rust
  • Sagging or spongy roof
  • Loose shingles
  • Visible flashing
  • Energy bills increasing
  • Ice dams
  • Pockets of hold or cold areas indoors
  • Hot ceiling
  • Overworked HVAC unit
  • Roof is hot to the touch
  • Wildlife in your house

Too much ventilation strains your HVAC unit. Intake and exhaust roof vents should have a 1:1 ratio, so for every exhaust vent, you should have one intake vent. Although in some cases certain homes may need an intake and exhaust roof vent ratio of 2:1 instead. Remember that it is always better to have more intake vents than exhaust vents. 

Benefits of Roof Ventilation

vent on top of a roof
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Roof vents are a critical component to your roofing system that offer a variety of benefits. 

  • Extends roof lifespan. Without roofing ventilation, heat trapped in your attic bakes roof shingles from below, causing shingles to age prematurely, which decreases the overall life of your roof. Overheated attics can damage rafters, wood framing, underlayment, insulation, and shingles. 
  • Prevents mold. Without a channel for moisture to exit your attic, moisture gets trapped in your attic and results in mold growth. This damages the attic space and poses a health risk to the home’s inhabitants.
  • Reduces energy bills. Proper ventilation keeps the attic cool by stopping it from overheating, which puts less strain on the air conditioning unit. This in turn decreases the amount homeowners have to spend on energy bills. 
  • Prevents ice dams. During a snowstorm, heat rises to the top of your roof and melts the snow, which slides down and refreezes at the edge of the roof. All this icemelt refreezing eventually creates an ice dam that stops ice and snow from draining off your roof. To prevent this, roof vents even out temperatures between your attic and the outside air so that trapped warm air isn’t melting snow at the top of your roof. 
  • Regulates room temperatures. If you have bad attic ventilation, you might notice that some of your rooms have pockets that are a significantly lower or higher temperature than the rest of the house. These uneven temperatures are usually caused by poor ventilation. 
  • Avoids overworking the HVAC unit. Roof vents keep the house cooler, which puts much less strain on your air conditioner. The HVAC unit will last longer and require fewer repairs.

Cost to Install a Roof Vent

The price of a roof vent varies depending on the type of vent, but roof vent prices usually range from $297 to $583. The national average price for a new roof vent is $440. Adding a roof vent cover or an attic fan will be additional expenses. Some other factors that affect roof vents prices are:

  • Roof size
  • Pitch of the roof
  • Roof design 

If you’re trying to decide what type of roof vent to get, here a list of the different types of roof vents and their prices:

Type of Roof VentTypical Price Range (including labor)
Box$53 – $197
Turbine$58 – $250
Dormer$73 – $283
Power$233 – $1,100
Cupola$163 – $837
Gable$85 – $265
Ridge$297 – $583
Solar$318 – $1,200
Soffit$297 – $413

FAQs About Roof Vents

Do flat roofs need ventilation?

There are two types of  flat roofs: warm roofs and cold roofs. The distinction between the types is based on the difference in their construction, as the insulation is located in different places for both flat roof types:

Hot flat roofs have insulation placed on top of the roof deck, which gives them better thermal efficiency. Hot flat roofs don’t need roof ventilation. 
Cold flat roofs have insulation installed underneath the roof deck. This allows air to pass through the roof decking on top, cooling down your roof, though it isn’t as energy efficient as a hot roof. They need roof vents to prevent moisture buildup and to keep the air inside from getting stale.

Should you cover roof vents during the winter?

Don’t cover your roof vents during winter. Although it may sound like a good way to keep your house warmer during the winter, good roof ventilation is just as necessary during the winter as it is in the summer. It’s actually better for your ventilation system to keep the attic temperature cool during the winter, as this reduces the chance of ice dams forming on your roof. 

Additionally, condensation is especially likely to build up in your attic during damp winters, so your roofing system will need good airflow to prevent water damage in your attic. 

What if rain gets into a roof vent?

Rain shouldn’t get into a roof vent, since roof vents are sealed to prevent rain from leaking inside. If a roof vent leaks, it means the roof vent is damaged or has been knocked askew by rough weather conditions. If rainwater is leaking into your attic, you should see about getting your roof vent repaired or replaced. 

Get Your Roof Vents Installed

There are many different types of roof vents, and roofs need the right number of intake and exhaust vents for proper ventilation. Roof vents improve your attic air circulation and are always working to protect your home from water damage and overheating. 
If you want to install roof vents on your home or if your current roof vent needs repairs, don’t hesitate to find a local roofing professional right away.

Photo Credit: Onfokus / Canva Pro / License

Danielle Gorski

Danielle Gorski lives with her family in Texas. She has a degree in Professional Studies and a minor in marketing. Her hobbies include reading, drawing, and writing.