Attic Ventilation BasicsReed Herman
Sep 03, 2020
When you think of your home, the last thing you probably imagine is that it can breathe. Well, maybe not literally breathe, but it does have a way of moving air in and out, whether you like it or not. One of the most important, and intentional, places for this to happen is in your attic. Attic ventilation is key to exceptional climate control in your home. This may seem a bit counter-intuitive; wouldn’t you want to keep all the warm air trapped up there when it’s cold?
Attics and Heat Retention
In an unfinished attic, the insulation that lays on top of your living areas is generally what keeps your home warm. The space above that is kind of a heat sink, just a place for the warm air in the summer (and, on a bright day, in the winter) to collect and move out of your living space. Since you can’t really have a safe indoor space without a roof on it, it makes sense to have a holding space that keeps all the warm and moist air tucked out of the way.
But the more of that hot air that accumulates in your attic, the warmer your home can become. In the summer, that excess heat can cause your shingles to age prematurely. In the winter, extra heat may not seem like a bad thing, but hot attics with poor rafter insulation can cause rapid roof snow melts, which turn into ice dams when the water refreezes at night. On top of that, warm air can hold a lot more moisture than cooler air; that moisture is the absolute enemy of wood, especially in an unfinished space. In short, overheated attic spaces aren’t great for your house, inside or out.
Attic vents were developed to help deal with this problem of too much heat accumulating in unfinished attics, where it doesn’t belong. There are many different kinds on the market today, but they all have the same end goal of moving cooler outside air into your attic and pushing that hotter air out (known as the stack effect).
When you’re looking for an attic vent, remember that it’s more than just the exit vent; you’ll need vents to bring cool air in, too. In many homes, these intake vents come in the form of soffit vents. These simple, easy to install vents let cool air come in to replace the hot air in your attic, which escapes through either a roof-mounted vent or a gable-mounted vent. That’s how a house breathes: soffit vents bring in cool air and roof vents let out warm air. In and out, in and out, helping to keep the climate in your home much more stable and drier than an exit vent alone would allow.
In older homes, enlarging your gable vents may be enough to create the airflow you need, especially if your home is short on overhangs to install soffit vents. How much to enlarge them is pretty subjective, but a good rule of thumb is that you should have one square foot of attic ventilation per 300 square feet of ceiling space. A lot of factors can influence this number, but it’ll never be lower than 1:300.
Venting your attic can be a challenge, even for the most experienced homeowner. Getting things just right can require complicated calculations based on the unique geometry of your attic and a solid understanding of the latest ventilation technology available.