Everything You Need To Know About Roof Ventilation

by Editor on June 7, 2013

arne jacobsen, almegaarden farmhouse, lumsås 1951-1953

A poorly constructed roof and attic can lead to destructive forces easily causing damage on your home, not to mention a lot of headache. Many times roof damage is a result of poor ventilation on the roof or in the attic. An unventilated or improperly ventilated roof can lead to problems such as mold, rot, and ice dams.

Roof Ventilation is Important No Matter Where You Live

Roof venting varies depending on where you live and climate conditions, but all roofs need some type of venting.

In cold climates, you need ventilation to avoid those ice dams that are created by melting snow. Any moisture that moves from the house to the attic to the roof and from outside can cause damage if the roof isn’t properly ventilated.

In hot climates, proper roof ventilation will release heat, moisture, and vapor buildup from the house and attic, which will also help to relieve the strain on the building’s cooling systems.

Your Existing Ventilation Depends on The Age of Your Home

Today’s building codes specify an exact minimum amount of attic ventilation needed to prevent moisture buildup on the roof, but older homes are often built without adequate attic and roof ventilation.

The Types of Roof Ventilation

The concept of venting is to create a continuous flow of air along the underside of the roof, with enough openings to completely recycle the air in your attic every few minutes. Most roof ventilation systems are categorized into two types for summer and winter needs:

  • Exhaust vents – vents that are installed in the roof to allow attic air to escape.
  • Intake vents – vents placed along the soffit, or the arch, to allow fresh air into the attic.

The Types of Intake Vents

Let’s look at the three types of intake vents out there:

Gable vents are the least effective type of vent because they circulate air only near the gables below the peak of the roof and not the entire roof expanse. These triangular-shaped vents are installed in the gable wall and can be good for high-peaked roofs.

Static vents, or “eyebrow vents,” are installed directly into the roof in rows by cutting holes into the fact of the roof and attaching them to the roof sheathing. They can be quite effective if many are installed, but as with any roof penetration, they can cause roof leakage.

Soffit vents are installed into rectangular openings cut into the soffit, or the underside of the roof arches. They usually include a screen to keep away insects and are made to fit between 16” and 24” center rafters. One type of soffit vent is a circular vent that is installed by drilling holes around one to eight inches in diameter in the soffit and positioning the vent into the holes.

Exhaust Vents

There are two types of exhaust vents: static vents, which just release air, and power vents, which actively suck air out. Both of these types of vents can include:

Ridge vents are installed along the length of the roof peak. Most builders agree that a ridge vent system, combined with under eave or soffit venting is not only the most effective type of vent out there but also less costly to install.

Power Ventilators are good for windy areas and high buildings. They are installed along the face of the roof similar to roof line venting and consist of a sheet metal cylinder with a mounted turbine engine. Wind spins the turbine, drawing air out of the attic.

The number of vents you will need depends on the type and size of the vents. Vents are rated by their “free vent area” (FVA), or the amount of square inches of open space the vent provides. Almost all manufacturers provide product FVA ratings as well as ventilation recommendations.

About the Author

This article was contributed to by blogger and home improvement expert Nicole Johnson. Nicole is part of the team at AirRoofing.com, a company that installs whirlybirds in Perth, Australia.

photo by: seier+seier

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