Roof Ventilation 101

When you own a home, one of the first things you learn is the importance of ventilation. If your bathroom isn’t properly vented, you’ll wage never-ending war against mildew growth. If your kitchen ventilation system is inadequate (or nonexistent), the smells from each night’s dinner will linger for days. And if your roof isn’t vented, you’ll face a host of problems, on both the inside and the outside of your house.

Fortunately, ventilation problems around the house aren’t too difficult for an experienced contractor to correct. Should the builder have ensured that the correct ventilation systems were in place from the very beginning? Or course. But things don’t always go that smoothly.

If you find that your home is warmer in the summer and chillier in the winter than you’d prefer, or if you’ve ventured into the attic in July only to be hit with a wall of staggeringly hot air, your roof may not be vented adequately (or at all).

How will you know if your roof needs ventilation? Not sure which ventilation system will work best for your house? Keep reading!

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Why Is Roof Ventilation Important?

In spite of the emphasis on air sealing and insulation to increase your home’s energy efficiency, your house isn’t actually meant to be a hermetically sealed box. Airflow is important in a house, especially through the attic and roof.

Warm air rises, so if your attic isn’t properly insulated or vented, your home will be subject to the negative effects of trapped hot air throughout the year.

In the summer:

• Heat builds up in the attic, overheating the roof decking and the ceilings in your home
• Exterior roofing materials and shingles age more quickly due to prolonged heat exposure
• Heat buildup in the attic transfers to the interior of the house, which forces the air conditioning system to work harder

In the winter:

• Warm, moist air from the house seeps into the attic
• Condensation develops in the attic and on the roof’s interior structural elements, which can cause wood rot and deterioration as well as mold and mildew growth on attic insulation
• Warm air causes snow on the roof to melt and refreeze at the eaves in the form of ice dams

An adequately vented roof and attic helps extend the lifespan of two of the most expensive systems in your house: the HVAC system and the roof. It also helps maintain good indoor air quality, since stuffy, humid air is continuously moved through the house into the outdoors.

If you want a healthier, more efficient home, put roof ventilation on your home improvement priority list.

Signs of Inadequate Roof Ventilation

If you’re not sure you would recognize an inadequately vented roof and attic area, keep these giveaway signs in mind:

1. Ice dams in the winter

Ice dams occur when snow melts on a roof, runs down the roof’s slope, and freezes at the eaves. Water expands as it freezes, and these patches of ice can damage roofing materials and cause leaks. A poorly vented roof and attic is warm at the top and cold at the bottom, which allows this melt/freeze cycle to continue.

2. Compressed or damp insulation

Insulation needs to stay fluffy and dry to do its job. When insulation gets wet, it compresses and loses some of its insulating ability. Wet or damp insulation is often a sign of condensation in the attic, which is a result of inadequate ventilation.

3. Water stains, mildew, or mold on wooden rafters, beams, and decking

Water (or even excess moisture) has no place in your attic. If you see signs of water damage on attic structural elements or the underside of your roof, your home likely needs better roof ventilation.

4. Frost on wooden rafters and beams

Frost in your attic or on the underside of your roof is a clear sign that moist air is getting trapped in your attic.

If your attic is accessible, taking a look around periodically is a good idea. Take note of anything that looks out of the ordinary, and call an experienced roofing contractor to investigate further.

Roof Ventilation Options

If you suspect that your roof needs additional ventilation, your first step should be to arrange a roof inspection with an experienced, reliable local roofing contractor.

Roof problems aren’t easy to diagnose on your own, and the heights involved in taking a close look at the condition of the shingles require extension ladders and safety equipment. Don’t risk your safety—let the pros take the lead.

Once your roofing contractor confirms the need for a ventilation system, he or she will recommend a type of vent (or a combination of different types of vents). There are a variety of roof vents on the market, and they all do essentially the same thing: Circulate hot, moist air out of your attic.

The key to getting the best roof ventilation system is to work with a roofer who will customize the project to the design of your roof. Here are the types of vents your roofer will discuss with you:

Ridge vent

A ridge vent has a low profile, so unless you’ve been driving around your neighborhood looking carefully at your neighbors’ roofs, you probably haven’t seen one up close. Ridge vents are installed at the very top of a roof, along the ridgeline.

Think of a ridge vent as a stationary hinge: It covers the space where the two sides of a roof meet and provides a way for stale air to circulate out of the attic while preventing precipitation and critters from getting in.

Soffit vent

Soffit vents are sometimes installed alone to increase the flow of fresh air into an attic space, but they are most effective when used in combination with ridge or box vents. While most vents are installed at the top of the roof, soffit vents are installed at the bottom edge, just under the eaves.

Box vent

Box vents look just as you might expect. They are low-profile boxes installed toward the top of the roof to vent hot air out of the attic space.

An individual box vent does not provide much venting space, so depending on the size of your roof, your roofer will likely recommend installing multiple box vents. Your roofer will help you decide on the best color for the vents as well as whether to purchase the metal or plastic version.

Turbine vent

Turbine vents are not low profile, but in windy climates, they provide more ventilation than other types of roof vents. On a windy day, the vent’s turbine mechanism spins, which moves hot attic air up and out.

The downside to turbine vents is that they don’t provide much venting power on calm days. As the vents age, their moving parts can start to break down, causing the turbine to be noisy or stop working altogether.

Off-ridge vent

From a distance, off-ridge vents look similar to box vents, but their design is slightly different. Off-ridge vents are usually rectangular in shape. They fill the same function as box vents and often need to be installed in multiples to provide sufficient ventilation for the average roof.

Gable vent

This type of vent is typically installed while a house is built and serves both a functional and aesthetic purpose.

Cupola vent

Cupola vents are similar to gable vents in that they’re usually part of the home’s original architecture. These vents provide a space for hot air to exit the attic, but because there is usually only one cupola per roof, they work best when used with another vent type.

Power vent

Power vents require electricity to function. In most cases, this type of vent is wired directly into the home’s electrical system, but solar options are gaining market share.

For efficiency purposes, power vents should be controlled by both a thermometer and a humidistat to ensure that the vent does not run when it isn’t needed. If the vent’s use of electricity is a concern, opt for a solar-powered version.

Best Roof Ventilation Methods

The truth is that there really isn’t a “better” or “worse” ventilation method that applies to all roofs. Regional climates and house architectural styles differ widely across the US, so what works for your relatives in the Northeast may not be the best option for your home in the deep South.

For all roof designs, however, the most important feature of a roof ventilation system is adequate and balanced airflow. What exactly does that mean? In short, an adequate and balanced ventilation system is one that allows an equal amount of air to enter and exit the attic area. The exact number of intake and exhaust vents your roof needs is figured based on the square footage and volume of the attic area.

The goal of roof ventilation is to get fresh, relatively cool air into the attic and vent out hot, moist air. And since hot air rises—and is exactly what you want to vent out of your attic—exhaust vents should always be installed at or near the top of the roof. Intake vents work best when installed at the soffits, which are the roof’s lowest points.

Regardless of the exact vent styles your contractor recommends, a roof ventilation system that does its job must include intake vents and exhaust vents.

The Bottom Line

An unvented (or poorly vented) roof and attic area is a ticking time bomb of sorts. Over time, moist, hot air trapped in the attic will cause serious problems, including mildew growth, structural deterioration, and degradation of important roofing materials.

Have your roof inspected by a professional every few years to catch small problems before they worsen, and always have any signs of moisture intrusion in the attic checked out. Installing or upgrading your roof ventilation system might not be the flashiest home improvement you can make, but the benefits for your home and its major systems are undeniable.