Common Residential Roof Vent Install Mistakes

Roof vents form the base of a home’s attic ventilation system, helping it breathe while preventing roof system damage year-round. That’s why it’s important to understand how the various components work together to create a balanced, effective attic ventilation system. Here are roofers’ most common residential roof vent install mistakes and how to avoid them.

Mistake #1 – Intake Vents Too High, or Exhaust Vents Too Low

A balanced attic ventilation system draws in fresh, cool air at the lowest part of the attic space and exhausts warm, moist air at the highest point. Incorrectly positioned exhaust or intake vents compromise the entire attic space’s exposure to continuous airflow, reducing overall system effectiveness.

Exhaust vents placed too low on the roof, two or more vents stacked, and consequently, one of the exhaust vents acting as an intake might disrupt—or short-circuit—the airflow path through the entire attic space.

Place intake vents at the lowest possible points of the roof, usually at or near soffits or fascia. Conversely, place exhaust vents at the highest possible point on the roof, always at or near the ridge.

Mistake #2 – Mixing Exhaust Vent Types Within the Same Attic Space

Two or more different exhaust vent types within the same attic space can also short-circuit proper airflow. When this happens, some of the exhaust vents may act as intake vents, restricting airflow to only the part of the attic space underneath those exhaust vents. Mixing exhaust products could also allow weather or debris to infiltrate the home.

Installing the wrong type of roof vent for a specific roof design can lead to mixing vent types to attempt correction. For example, a ridge vent installed on a hip roof with very little ridge line, may not provide enough exhaust for the attic space. Additional louvers or power vents may add more exhaust but disrupt the airflow volume or balance. Mixing Vent products or types requires careful planning, or it can lead to problems.

A best practice is to install one type of exhaust vent in the attic space that meets the exhaust NFVA (net-free ventilating area) requirements, allowing the air to flow continuously throughout the space.

Mistake #3 – Ridge Vent Opening Too Long

Long ridge vents installed across long roof ridge lines should have only enough vent slots open to provide the required amount of exhaust. Installing a ridge vent along an entire roof ridge is nice for a consistent look, but opening too much vent to exhaust is a common mistake. Cutting an opening that’s too long leads to too much exhaust, disrupting the balance of the entire ventilation system.

The opening of the ridge air slot needs to match the amount of exhaust NFVA required for a specific attic space. For example, an attic space requiring 288 square inches of exhaust has a 40ft long ridge. 4-foot plastic ridge vents each provide 18 sq. in. per linear foot. Of the 10 sections of ridge vent, only 4 sections or 16 ft will have the slots cut open. Only 16 ft. of the 40-ft. ridge. 16ft x 18 sq in. = 288 sq in. of exhaust.

Open Ridge Vent air slots according to the required exhaust NFVA for the attic space and balanced with the same intake NFVA.

Mistake #4 – Clogged or Blocked Intake Vents

Intake vents become ineffective if the outside portion becomes clogged with paint, dirt, dust, or spiderwebs. Vents commonly become blocked from the inside when attic insulation covers them.

Remove debris accumulated over time and keep the intake vents clean. Likewise, attic baffles should keep insulation away from the intake vents. Check that a hole has been properly cut in the soffits to allow air to enter via the intake vents.

Mistake #5 – Missing or Inadequate Intake Vents

Arguably, intake is the most important part of an attic ventilation system. Therefore, when there is inadequate intake—or none—an exhaust vent may not function properly.

Static exhaust vents, like ridge vents or roof louvers, hinge on adequate intake. Similarly, the same goes for powered exhaust vents, which will have to work too hard to pull air through the attic space, resulting in the premature failure of the power vent’s motor.

Always check that you have a balanced attic ventilation system with the proper intake and exhaust ventilation for the ventilated attic space.

Mistake #6 – Blindly Copying Existing Vents Without Checking

Another common residential roof vent installation mistake is not double-checking ventilation requirements before writing the proposal. Homeowners depend on roofing professionals to guide and advise them on maximizing the value and function of their replacement roofs. It’s a mistake to ignore this important responsibility. Do not assume the current installation of vents is correct or balanced. Double-check.

There is no better time than during a roof replacement to correct any wrongs or to make aesthetic improvements to the roof hardware. Most homeowners do not know what options they might have to improve their roof’s look.

Free Online Ventilation Calculators

Most homeowners have a file stowed away with important papers and key information about their home. So, information like ventilation requirements is easily calculated (Button Below) once, recorded in the file, and stashed until the next roof repair or replacement. You just need measurements of your home’s attic area(s) in square feet.

The U.S. Federal Housing Authority recommends a minimum of 1 square foot of attic ventilation (evenly split between intake and exhaust) for every 300 square feet of attic floor space. Always have a balanced ventilation system. In no case should the amount of exhaust ventilation exceed the amount of intake ventilation. You can calculate the “Net Free Ventilating Area” or NFVA based on your attic measurements. Typically, you are looking for 1 sq foot of NFVA per 300 sq ft of attic*.

Divide the total NFVA evenly between the exhaust and intake. Your roof style will indicate the total intake and exhaust required in square inches. The intake and exhaust amounts should be balanced closely for optimal performance and benefit.

Knowing the required intake and exhaust your attic space(s) should have means you can evaluate what you currently have versus any changes you’d like to make.

You prefer replacing the gable vents with ridge vents for exhaust and soffit vents for intake. This change is no problem as long as the total meets your NFVA needs and the balance between exhaust and intake is preserved.

The GAF Ventilation Calculator button is free of charge to use.

* The local building code sometimes calls for 1 sq ft per 150 sq ft. Always follow local code.