Attic Ventilation Do’s and Don’ts

Attic ventilation is a confusing subject to most homeowners residing in the suburbs of Chicago. Some, especially those with newer roofing systems that use advanced insulation materials, tend to think that their attics are fine and they don’t need to take any extra measures to keep their attic sufficiently ventilated. Others care about attic ventilation only during the hot summer months, while a handful of homeowners are actually overdoing it regardless of the season.

Either way, it’s estimated that 90 percent of homes in the United States have unreasonably high levels of moisture in their attic. Moisture has a direct effect on their roofing structures and results in shorter lifespan of the roof or ends up causing mold all over the home. Below are some do’s and don’ts when it comes to your attic ventilation.

1. Do use proper attic fans in the winter, not only in the summer.

Most homeowners buy attic fans in the summer. That’s when they’re most concerned about venting hot air before it can build up and overheat their homes. But here’s a fact many people don’t know: attic fans are just as important, if not more so, in the winter. That’s when moisture accumulation tends to increase due to extreme temperature variances, and it can be just as damaging to a home as heat. This silent menace can prompt leaks, mold and fungus growth, insulation damage, and wood rot. 

An attic fan helps by equalizing the indoor and outdoor temperatures. By continually exchanging warm, moist air from inside the attic with cooler, drier air from the outside of the home, it prevents condensation from occurring. The ventilation process also helps to maintain even attic temperatures, which keeps ice dams from forming (the latter is super important during harsh Chicago winters).  

2. Don’t go crazy with roof vents.

Too many people believe the importance of roof ventilation is to increase energy efficiency during the summer. Good roof ventilation can do this, but shingle color, sun exposure and insulation are exponentially more important to overall energy efficiency than ventilation. Meanwhile, preventing moisture damage is a much greater benefit and applies to colder climates like the one in Chicago more than warmer ones. In fact, the colder the climate, the more likely it is that your home will benefit from proper attic ventilation. In order to install an unvented roofing system in colder climates, you’ll need highly rated, rigid insulation to prevent condensation on your roof sheathing. In warmer climates, you don’t need to worry about condensation.

3. Don’t assume that more ventilation is better.

Just like properly sizing your furnace and air conditioning unit, you want precisely the right amount of attic ventilation for your home. Insufficient ventilation can lead to moisture problems during the winter and decreased energy efficiency during the summer but too much ventilation can be just as bad, if not worse. Roof vents create an additional roof penetration, essentially another place of vulnerability where leaks can occur. Some vents are necessary, but you don’t want to needlessly increase the number of roof penetrations. More than leaks, these seams can cause blowouts during a hurricane or allow sparks from a wildfire to enter your home and set it ablaze.

3. Do ensure proper insulation.

Some homeowners believe that because heat rises, ventilating an attic space during the winter means you’re releasing warm air. However, poor insulation is usually the culprit, although if you enter the attic on a sunny winter day, your attic space can be warmed by the sun more than your furnace. Unless your roofing system has insulation on the roofing deck and is designed without ventilation, your furnace should not be heating your attic. Worse yet, inadequate insulation is almost surely allowing moisture-laden air into your attic. When this warm, moist air hits your roof, it’s likely to form condensation that will lead to further deterioration of your insulation and/or wood rot. If you think this might be a concern, wait till the sun goes down and measure the temperature in your attic. It should be pretty close to the outdoor temperature.

4. Don’t assume that roof vents equal ventilation.

OK, this one’s tricky. Vents=ventilation, right? Wrong! While hardly anybody agrees on the best roof ventilation system, everybody agrees some roof vents do hardly any good at all. Take, for example, ridge vents. The majority of roofing experts agree that ridge vents are the most effective and cost-effective roof vents available. Without baffles (blinders that prevent outside air from crossing over the vent), a ridge vent may create almost no ventilation at all. Gable vents may circulate air through only a small percentage of your attic. Static, roof-line, vents are effective for ventilation but generally aren’t recommended due to issues with leaks. Soffit vents may leave air trapped at the top of your attic. Most effective ventilation uses a ridge-and-soffit continuous ventilation system, but even these designs can vary from roof to roof.