Understanding Attic Ventilation
Attic ventilation is a confusing topic for many people, and not many actually understand how a well-ventilated attic contributes to a comfortable home. If attic insulation keeps your house warm, why should attic ventilation let in cold air? It seems counterintuitive, however, proper and continuous attic ventilation is a vital component in making your home comfortable all year round, so it's worth a little time to understand how it works. Here's the basics.
Why Is Attic Ventilation So Important?
Proper attic ventilation will ensure the the temperature and dew point of the air inside your attic and that of the air outside are close together. Wide variations will lead to higher heating and cooling bills as well as increased repair bills.
In warm climates, hot attics make your air conditioner work longer and harder and also shorten shingle life by heating them from the underside. In colder climates, moisture in your attic can cause condensation and frost to form on the underside of your roof. When the temperature warms up, the moisture drips onto the attic floor and gets into the insulation, reducing it's effectiveness.
Components of a Proper System
Insulation in the attic floor (the ceiling in your home) helps keep the treated (heated or cooled) air from your living space from getting up into the attic space. Likewise, vapor barriers keep the moisture in the air of your home from getting into the attic.
Because of the large number of openings in your ceiling (light fixtures, exhaust fans, attic door opening) some moisture will inevitably get into your attic. That's where ventilation comes into play. In the summer, it keeps the attic as cool as possible without air conditioning, and, in the winter, it gets rid of moisture and keeps the temperature in the attic the same as the outside.
So How Do You Get Proper Ventilation?
Air enters the attic at the bottom edge of the roof through openings called soffits and then flows up toward the top of the roof, where it exits through another vent (along with any heat or moisture it has picked up). Older homes usually have some form of attic ventilation (roof vents, whirlybirds), but since the rule of thumb for proper ventilation is to have 1 square foot of ventilation for every 300 square feet of space, this often isn't enough.
It's possible and relatively inexpensive to get better attic ventilation by adding vents, either through openings in the roof or in the end walls of the attic. However, many experts feel the best way to ventilate an attic is using ridge vents installed along the peak, or ridge, of the roof.