Roof Ventilation

A healthy roofing system begins with good ventilation. Proper ventilation helps to prevent damage, costly repairs and premature aging caused by moisture in the winter and excess heat in the summer. Good home ventilation also helps to regulate temperature, reduce backdrafts and protect respiratory health by venting stale air and lowering emissions and indoor pollutants.

So why is ventilation crucial when it comes to your roof? Let’s start with history and science.

Starting in the early- to mid-20th century then need for roofing ventilation was documented. That’s when organizations like the American Society of Heating, Refrigerating & Air-Conditioning Engineers (formerly ASHVE) and Forest Products Laboratory identified that building condensation problems could be caused by poor roof ventilation.

The basics of ventilation are pretty simple: it is the flow of air through a system of intake and exhaust. Proper ventilation only works when air flows. There are two key methods to create airflow within an attic:

  • Mechanical – this requires a power source.
  • Natural – natural roof ventilation is used whenever possible.

When creating natural ventilation, the stack effect and the wind effect work together to naturally circulate air. The stack effect happens when hot air rises and creates a higher pressure at high points in the attic. The hot air that escapes is exhaust. However, this hot air cannot get out without an inlet for cooler, low-pressure air. This cool air that enters is referred to as intake.

When wind blows against the outside of a roof and increases the volume of intake and exhaust, this is called the wind effect. Intake and exhaust produce the natural flow of air to create a well-vented attic.

Roof ventilation at work

Roof ventilation systems are unique to your home. Many factors including code requirements, regional climate and roof and ceiling designs all need to be considered when venting your roof.

There are two main types of roof ventilation – exhaust vents and intake vents.

Exhaust vents allow exhaust to escape.

Ridge vents are the most common type of exhaust vents. They are installed at the intersection of two roof planes (also known as ridges). They are usually made of molded, high-impact copolymer and are installed underneath a final layer of shingles giving the roof a seamless look.  To the untrained eye, ridge vents are almost invisible.

Visible exhaust vents that are mounted on the outside of your roof include louvers, gable louvers, wind turbines and power attic ventilators. Similar to ridge vents, roof louvers and gable louvers work without the use of electricity.

Wind turbines also do not need a power source, but they work best with a constant source of wind and are not as effective as ridge vents. Power attic ventilators require a power source and are an exhaust vent option for certain roof designs or areas without much wind.

Intake vents can be even harder to spot that exhaust vents.

Similar to the ridge vents, edge vents are also made of a copolymer material.  They are located at the edges of the roof, these intake vents can be installed at the eaves under the soffit, at the drip edge, or under the shingles at the roof’s edge. The intake vents work in conjunction with ridge vents to allow cool air to enter the attic space, forcing warm air to exit through the ridge vents.

Now that we’ve reviewed how ventilation works and how a roof can be properly vented, here are the benefits of roof ventilation.

1. Extends the life of your roof.

Have you had icicles build up on the edges of roofs and gutters? This buildup is known as ice damming and you can see the icicles, but you can’t see the damage that they’re doing to the edge of your roof.

Ice damming occurs when heat from inside your attic combines with heat from the sun to melt snow and ice on your warm roof. When that water runs to the edge of the roof, it begins to refreeze. As the ice and water build up at the edges of your roof, it can back up both behind and underneath the roofing materials, causing damage to your whole roof system, your attic and even the walls of your home.

Proper ventilation lets this warm air escape before it has a chance to melt the snow and ice on your roof.  A well-vented roof is easy to see in the winter months – it may have snow on the roof but there is not an icicle in sight.

Ventilation matters when it is hot outside as well. When it is hot outside, the temperature on your roof can be nearly double and a hot roof over a poorly vented attic translates into a very hot attic.

Why? Poor ventilated attic spaces don’t have an escape route for the heat that builds up. This buildup of heat can cause damage to your shingles from the inside out. An evenly vented roof lets the hot air escape keeping your roof and attic cooler.

2. Reduces energy costs.

When the temperatures start to climb outside, we all want to stay cool inside. A properly vented roof allows heat to escape, which in turn reduces the workload on your air conditioner. This impacts your wallet: an air conditioner that’s running less means a lower electric bill.

3. Reduces extremes in indoor temperatures.

When you walk upstairs does it feel at least 10 degrees warmer than it was in your living room? If you live in a ranch-style homes you may also notice that although the room doesn’t feel cool, your feet are as cold as ice.

These indoor temperature extremes are typically the result of poorly vented roofs. When your roof is adequately vented to allow the hot air to escape and the cool air to enter the attic space, your home will be more comfortable year-round.