Explained: Active, Passive, and Mechanical Roof Ventilators

Written By Kenneth Wilson | 0 Comments

Proper roof ventilation is essential for maintaining clean, healthy air in our homes, aids energy efficiency, and can even affect your roof's structural health. That said, how do we achieve good ventilation? Roof ventilators come in three broad categories: active, passive, and mechanical, differing in how they operate.

Active, passive, and mechanical roof ventilators use different methods to exchange warm, stuffy air for clean, outdoor air via the attic. Passive ventilators rely on wind and convection; active types use intake and exhaust vents. Mechanical ventilators rely on power sources to move air around.

When renovating your roof, installing ventilators will ensure proper airflow, temperature control, and the removal of potentially hazardous pollutants from your home. To make an informed decision on which roof ventilator to choose, it's helpful to understand the different types and their pros and cons.

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Understanding Active, Passive, and Mechanical Roof Ventilators

Active roof ventilators use intake and exhaust vents.

Passive roof ventilation is also called natural ventilation.

Mechanical roof ventilators require power sources.

Final Thoughts

Understanding Active, Passive, and Mechanical Roof Ventilators

We can define ventilation as the exchange process between outdoor and indoor air. Roof ventilators allow buildings to breathe and minimize the risks of moisture buildup in the attic and the insulated house sealing in harmful pollutants and gases. Each type of roof ventilation system has its pros and cons.

Active roof ventilators use intake and exhaust vents.

Active roof ventilators can consist of moving or non-moving parts but do not depend on power sources to ventilate the attic. This type of ventilation draws fresh air from outside through intake vents and expels the warm, stale attic air via exhaust vents.

Different types of active roof ventilators are available on the market, with the turbine (whirlybird) and ridge (with baffles) varieties being the more popular options.

The whirlybird vent is wind-powered with a bulbous shape. The turbine has fins on the exterior, causing it to spin when the wind blows. It creates a vacuum, pushing warm air through the roof vents and cools the building while circulating the attic air 10–12 times per hour.

Many people believe the structure of these turbine systems allows debris, rain, snow, and birds to enter your attic, but this only happens with damaged ventilators, which you would then need to replace.

Homeowners often choose roof ridge vents with baffles (plastic flaps) because they don't compromise the roof's aesthetic. The contractors cut them into the roof ridge, making them inconspicuous, unlike other types that protrude from the roof. These vents need mechanical fans in the attic for optimal ventilation.

If you're considering active roof ventilation systems, keep the following pros and cons in mind:

BENEFITS

Some active roof ventilators, such as the tower variety, don't have moving parts. Its height allows it to consistently remove heat from the attic throughout the year because it sticks out above the snow accumulations.
Tower ventilators also prevent water or snow infiltrations because of their anti-gust deflectors.
Active ventilators don't require energy to operate, so they can help reduce energy bills during the summer.
Active roof ventilators are usually constructed of aluminum or galvanized steel, making them resistant to rodent penetration.

DRAWBACKS

Active ventilators with moving parts can be noisy.
Whirlybirds depend on their turbines to ventilate the attic but may freeze during harsh winter conditions. This reduces their efficiency.
Some active roof ventilators are not as pleasing to the eye because they stand out above the rooftop. The Whirlybird and tower ventilators are examples.

Passive roof ventilation is also called natural ventilation.

Passive ventilation means natural sources like wind and convection to shift the air around in the attic. Fresh air typically flows through soffit vents, causing the hot, humid air to rise and escape via the passive vents at the roof's highest points.

Passive systems also sometimes depend on wind-driven ventilation, with winds entering the soffits in cross-sectional directions, causing a positive pressure inside the attic. This forces the moisture and heat to rise, where it escapes through the high vents.

Examples of passive roof ventilators include gable vents, soffit vents, static or turtle vents, dormer vents, and ridge vents without baffles.

BENEFITS

They don't have moving parts.
Passive roof ventilators are not noisy.
They require very little maintenance.
Passive ventilators are more pleasing to the eye because they are discretely placed and blend in with the building.

DRAWBACKS

Plastic vents are more prone to rodent intrusions.
Snow quickly covers passive ventilators, and the attic heat causes ice dams.
Often, there are insufficient vents to evacuate the air from the attic adequately.
If there's not enough wind to force fresh air into the attic, ventilation will be slow and inefficient.

Mechanical roof ventilators require power sources.

Mechanical roof ventilators require energy to operate. Power sources could be electricity or solar power. These vents operate in the same manner as their passive and active cousins, except that the power vents draw the moist air from the attic at a specific volume.

Power vents are round, sit near the roof ridge, and use electricity to cool your attic and reduce the humidity, minimizing the risk of damaged timber and drywall. Using a humidistat with power vents during winter is advisable to maintain appropriate humidity levels.

Solar-powered vents rely on the sun to generate the energy necessary to run. Many homeowners opt for solar power instead of electricity, which extends to the vents.

BENEFITS

They can offer energy bill savings during summer.
Mechanical vents are very efficient at keeping attics cool and controlling the humidity.

DRAWBACKS

Some mechanical ventilation systems are noisy.
You can expect the motors to fail after a few years due to continuous running.
Solar-powered vents don't work while the battery charges, leaving it less efficient on cloudy days. They also won't work during the night.

Final Thoughts

Homeowners may sometimes dismiss the attic as an insignificant part of the house. However, it plays a vital role in efficient roof ventilation, providing healthy indoor air quality and energy efficiency.

Now that the differences between active, passive, and mechanical roof ventilators and their pros and cons are apparent, making the appropriate choice for your home will be simple. (Related article: Can Attic Ventilation Save Cooling Costs?)

About the Author

Kenneth Wilson

I can build it, and I can help you get the patio enclosure you want! I got my start in the Florida patio industry back in the 70s as a young general laborer looking for something to make a few bucks. At the time I never thought it would end up as my career. Over the years I grew beyond the laborer position, becoming a foreman, superintendent, and then into executive management for some of the largest patio contractors, and material vendors. Now into retirement and slightly bored, I offer consulting services to new and existing contractors, and publish this website to help the people who love their patio's and screen enclosures the most - YOU!