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Roof Ventilation: The Good, Bad and Ugly

Posted March 8, 2011 by Patrick Morin
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The roof is typically a second thought for many homeowners. However, it’s one of the most important parts of a home that protects you and your family from things like harsh weather conditions and wild animals. 

One of the most important ways to ensure your roof stays in top condition is to have adequate roof ventilation. It not only prolongs its lifetime use but also helps your HVAC system, not to overwork.

But what exactly is a proper roof or attic ventilation system? At its most basic, it’s essentially a system that uses intake and exhaust vents to ensure fresh air circulation. 

Every home in the US will use one of two systems:

  • Natural
  • Mechanical

The first type, natural attic ventilation systems, seem to contradict themselves. Roofs and attics that use a natural system need to be insulated for warmth but simultaneously require soffit and rafter vents to maintain airflow. 

It may not seem evident at first, but the combination of insulation and airflow through the vents helps create a durable roof and an energy-efficient home. 

For example, during winter, the natural outdoor air helps keep the attic cold, reducing and even preventing damages caused by ice damming. The airflow also helps keep the hot air moving out of the attic during the summer, preventing moisture from collecting and protecting the roof shingles. 

Essentially, these systems use natural airflow and thermodynamics to regulate ventilation. 

Unlike natural systems that use passive airflow, mechanical systems take a more controlled approach by using a fan or motor-driven vent. These vents or fans cool hot attics and roofs by drawing in cool air and pushing out hot air. 

However, these motorized fans may suck up cool air from your air conditioner into the attic if your home isn’t appropriately sealed or if your soffit vents are blocked. This is something to be aware of because it will use more energy and increase your summer utility bills. 

Why Roof Ventilation Is So Important

Roof ventilation is important for many reasons. The most significant benefits of roof vents include:

  • An increased roof lifespan
  • Reduced HVAC workload
  • Ice dam protection
  • Reduced energy costs
  • Protection from extreme indoor temperatures

Increased Roof Lifespan

As briefly mentioned earlier, inadequate ventilation can dramatically reduce your roof’s lifetime use. Oftentimes, the reduction is due to excess heat in attics. The extreme heat will eventually cause damage to the interior surface, including the underlayment, framing and rafters. 

The interior damage will then cause the shingles on your roof to dry and crack much sooner than expected. Of course, all roofs will deteriorate over time, but that timeline is rapidly brought forward without proper ventilation.

Less Work for HVAC System

Excess heat drastically reduces your roof’s lifespan and can also affect your HVAC system’s energy efficiency. As briefly mentioned earlier, blocked vents and improper sealing can cause your HVAC system to overwork and use more energy. 

To prevent your attic from being cooled by your air conditioner, ensure your attic is sealed off from the rest of the house and that all vents have an unobstructed flow of passive air. 

Ultimately, proper ventilation helps reduces your summer energy bills and keeps the rest of the house nice and cool. 

Moisture & Mold

One of the most important reasons to have adequate roof ventilation is to prevent damage caused by mold and moisture. Whether you live in a rainier climate like Portland, Oregon or a state that goes through harsh winters, condensation will present a mold problem. 

Condensation from the warm air rising and hitting the cold surface of your attic and roof will lead to moisture build-up if there isn’t proper ventilation. The moisture build-up will then lead to costly damages like mold, structural damage to the roof itself and stained ceilings. 

Generally, if the moisture and mold go undetected for some time, you may end up having to replace your entire roof. 

Ice Dams

Although icicles are beautiful in paintings and something you’d expect to see on a cabin deep in the woods, they’re not something you want hanging off your roof. 

If your roof has icicles, it’s a sure sign of ice damming caused by inadequate roof ventilation. This occurs when your attic’s airflow is blocked and retains all the hot air generated by your heating system from below. 

Eventually, the trapped hot air will heat your roof and cause the snow to melt. The melted water will then flow into the gutter system, where it will refreeze. 

Each melting and refreezing cycle will eventually cause water to back up and flow into the attic, causing expensive water damage. 

Attic Vent Types

Roof ventilation is clearly an important part of keeping your home intact and in top shape. But what about the vents themselves? Which one is the most beneficial for your specific home? 

When discussing a new vent with a roofing specialist, you’ll likely discuss one of the following: 

  • Louvers
  • Turbines
  • Gable vents
  • Power fans
  • Ridge vents


A louver is a type of vent that allows air to flow through while keeping out dirt and debris. It’s the most economical option, and homes that use this vent type will either use a series of box vents or an Italian-style copula louver vent. 

A home using box vents will require them to be installed in groups across the roof for extra ventilation. Having one or two boxes is never enough to vent an entire roof or attic! 

Although their smaller size may be a drawback, it offers excellent versatility due to their ability to be strategically placed in smaller areas. However, with louvers, dead spots are unavoidable, and the multiple vents may end up fighting each other for airflow.  

The second type of louver is a cupola vent, and it’s also the least common. This is because cupola vents were designed specifically for barns and can be costly and complex to install. 

Generally, cupola vents don’t make much sense for most homes unless you’re looking to add curb appeal.


Roof turbines are an extremely efficient and low-cost solution to ventilate your roof or attic year-round. However, there are a few drawbacks to this type of vent. 

First, roof turbines require a minimum of five miles per hour winds to activate and spin. That means on low or no wind days; it won’t be effective at all. 

If you happen to live in a low-wind area, then you may want to consider another vent option in addition to the roof turbines to help air circulation on hot summer days. Roof turbines are also prone to noise and squeaking and will require occasional lubing.

However, overall, turbines are an effective and eco-friendly way to ventilate your roof with minimal maintenance and upkeep. 

Gable Vents

Gable vents are an older but reliable form of intake vent. These vents use cross ventilation to keep air flowing and are usually only used on gable-style roofs. This is because gable roofs allow these vents to be placed on either side. 

Although low-maintenance, it’s not ideal for more complex designs like hip or valley roofs. This is because the other design features may impede the cross breeze, leading to inadequate airflow.  

Power Fans

Power fans or attic power vents use electricity to power the propellers to pull air out of an attic. These low-profile vents are thermostat-controlled and pull the stale attic air from a central point but come at the cost of higher utility bills. 

However, power fans have the potential to create negative pressure, which can lead to gas intrusions such as radon or natural gas. If you use a power fan, you must also ensure that it’s powerful enough to actually dispel the stale air. 

If you have a weaker power fan, it can be just as damaging as having a strong one. Weak fans will circulate the air rather than carry it out of the attic space, making it not worth the cost. 

Ridge Vents

The most common type of exhaust vent for modern homes is a ridge vent. Although it’s the most expensive option, it provides constant, passive airflow throughout the length of the entire roof. 

That means you won’t find any dead spots with a ridge vent. This is important because ridge and other types of exhaust vents dispel the hot, humid air that causes all the potential damage to your roof!

Roof & Attic Ventilation in Portland, OR

Each home will have its own airflow and a specific roof design. That’s why it’s essential to use the right type of vent to reap all the benefits of roof ventilation. If you think you may have a ventilation issue, get in contact with our specialists for expertise in determining the best and most efficient vent for your roof in Portland, you can count on.

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