What Roof Vents are Best?
Attic cutaway showing how air moves through the soffit and exhausts through a ridge-vent style roof vent Image Credit: A Crash Course in Roof Venting-Joseph Lstiburek
Learn How Different Roof Vents Work and Which is Best For You
The most important thing with roof vents is making sure the home actually has them! Several cheap plastic roof vents are better than not having anything at all. To dive into what makes one vent better than another is understanding the science behind roof ventilation first. Roof vents have a purpose that is about as important as the shingle themselves. In many instances, building inspectors couldn’t care less about the shingles but focus on whether the ventilation was done properly and the pictures of the underlayment and roof deck are available. Most of the roof vents don’t work effectively by themselves. Two parts are required for effective attic ventilation: Intake (soffits) and Exhaust (Roof vents). Ventilation that is not adequate will resort to all kinds of problems that may not be seen in the summer months but ultimately manifests in the winter forming ice dams and condensation. Ice dams and fixing them covers this common ventilation issue.
Roof ventilation is the system that allows air to exchange in the attic space. The goal of the attic space is to match the ambient temperature outside the structure. When attic spaces get too hot, asphalt shingles can cook and blister from beneath, especially pre 2000 shingles. In the winter, an attic that’s missing key elements such as ventilation will cause frost in the attic. Why is Frost in my Attic? To reiterate, any vents are better than no vents, but there is a method to making them perform.
When installing a new roof, ventilation is often mimicked to what the home had on it before. This is often wrong! Simply hiring a company that only thinks roofing is laying one shingle next to the other without understanding building science can end in disaster.
Roof vents, ridge vents, power roof vents, and bathroom vents are the exhaust of your home. They get the moisture out of the attic keeping mold at bay and keeping the roof deck intact and rot-free! If you’ve ever wondered what those perforations are under the overhang along with your house, they are an important part of the system. They are the intake. Air sucks in those little holes and circulates through the attic, and exhausts out the roof vent. Without this system, the air stays stagnant. The system hangs in the balance and can be disrupted by anyone who doesn’t understand how roof ventilation works. A guy blowing insulation into an attic can block off the intake where the soffit vents are and stop air circulation instantly. A roofer who decides the more roof vents, the merrier can reverse the whole system. How, you might ask? A roof vent that was exhausting is now intaking air. Snow, rain, and dust can enter through the vents and collect on the insulation. Mixing roof vents also have repercussions. In conjunction with a standard box vent, a ridge-vent will exchange air with each other rendering the soffit ventilation unused until the situation changes. Low roof vents and high roof vents will do the same thing. At times, box vents can be used deliberately to help circulate air. We have installed low box vents and high box vents to achieve ventilation. Be aware of this because it is a good thing and maybe the only option in older homes.
Roof Vents for Every Situation and Application
Here are the most common roof vents and their application. Most exhaust vents can only operate effectively when there is an intake for them to pull air from. Without soffit vents, the air can “stack up” in the attic minimizing the effectiveness of exhaust vents. There is the best roof vent for different roof applications.
Ridge vents Popular because it looks good. This seems pretty shallow, but that is the case. These vents run along the ridge or peak of the home and exhaust heat via a long opening cut before installing on the roof. Ridge vents are often plastic and are used in conjunction with the cap shingles chosen to blend into the roof. These vents do offer a slight performance edge over typical box vents because they can draw air out on their own if the soffit vents are marginal. Certain ridge-vents have an external baffle that creates a low-pressure pocket to help move the air. Ridge-vents are not all created equal. I know of two that perform as advertised!
Box Vents or Turtle Vents Box roof vents are often used in groups and with homes with cut-up roofs or hip-style roofs without long ridge areas. Box vents are quite common and perform well only when a working soffit is available. They can be used to exchange air with each other on purpose in the attic and accidentally. The construction of these vents is plastic, aluminum, or galvanized. Galvanized is the best.
Gable Vents Gable vents commonly occur in older homes. These vents are not on the roof but cut in the sidewall of the home. Sometimes they are wooden with slats, sometimes metal. They are in pairs and transfer air through cross ventilation. Farmhouses or story and half homes did not have working soffits, as shown in the diagram. These vents took on the role of intake and exhaust. It can change daily by whatever direction the wind was from. This vent can work independently without soffit vents.
Power Vent: Power vents are just like big box vents with a built-in motor. Instead of needing multiples of the small vents, one power vent can do the job. Power vents can be solar-powered or be 110v and wired in the attic. They often run off of humidistat or temperature-controlled switches. Power vents physically pull air out of the attic. This vent can work well with a balanced ventilation system and marginal with minimal soffit ventilation. Marginal will result in limited motor life. The motor often overheats from an attic starved of fresh air. When the motor fails, nobody usually knows, and condensation and ice dams can be the result.
Whirly Bird or Wind Turbine: These roof vents are pulling air out of the attic as well. Instead of an electric motor, the wind spins the turbine creating a suction that pulls the air out. The best option with zero soffit ventilation. They are not an elegant addition to a roof and can be cumbersome and noisy when bearings go out. They do work!
Left to Right: Whirly Bird Vent, Powered Roof Vent, Ridge-Vent, Gable Vent, Box Vent
Bathroom and Range Roof Vents
Not having range vents or bathroom vents exhaust through the roof is detrimental to any attic. This causes moisture which will promote mold growth. Addressing this issue is important and the most commonly forgotten thing to do with any of these vents. “We always planned on hooking that up.” is a phrase I hear from homeowners all the time. Often I see the vent pipe lying in the soffit space, hoping this would remedy the situation. It is just the same as if in the middle of the attic! I hope an understanding is gaining some traction on what role the soffits play in ventilation.
Terminating these roof vents properly through the roof is a forgotten art. I’ve seen plastic vent pipes hanging on drywall screws in hopes exhausted air will magically find a way out. It’s as comparable as getting the sprayer nozzle close to hook up on the garden hose!
A bathroom roof vent terminated properly through the roof deck
The Importance of Roof Vents and Ventilation System Should Not Be Overlooked!
A ventilation system can be the difference between having weather actually occur inside your attic instead of keeping it outside the home where it belongs. Our job is to understand this part of the puzzle, which is far more complicated than just nailing shingles down.
Call Rooftop Solutions at (507) 400-ROOF to discuss how proper roof ventilation can solve potential headaches.
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