Attic ventilation is a critical component to maintaining even temperatures in your attic all year long. In the summer it saves on the life of your shingles by keeping the boards cooler and decreases your cooling costs in the winter weather by diminishing the temperature difference which in turn prevents moisture build up in the form of condensation. Did you know that having a proper amount of attic ventilation is even required to enforce the warranty of most shingle manufacturers?? When it comes to mold the most import ventilation concerns occur in the winter. In the winter during the coldest months as we run our furnaces, hot air escapes into the cold unheated attic space. When the escaping hot air emerges into the cold attic it rises as heat always does. It seeks out the highest portions of the attic where it then coalesces against the cold boards of the roof. This hot- air-mass-meets-cold-surface phenomena results in a condition known as dew point, which creates moisture in the form of water droplets and ice crystals. The nails themselves also will contribute to this moisture problem as iron is a good conductor of temperature and will readily convey the biting chill of cold winter air directly inside the attic. The evidence of this can be seen in the form of drips and of drip spots underneath the nails themselves.
Bathroom fans vented directly into the attic or Soffet areas rather than straight through the roof are also to blame for exacerbated moisture problems which lead to mold, wood- rot and health problems. The more adults showering in the house and the longer the showers the more moisture will enter an attic. In fact in some families the bathroom fans alone are the sole culprit responsible for major mold infestations!
If you want to eliminate attic mold permanently you need to get equal amounts of intake air and exhaust or out-take air into your attic.
Building scientists have proven that using a balanced ventilation system that utilizes equal amounts incoming and out going air. Incoming air comes in from under the eves through vents cut in the underside of the roof overhangs which are called soffets. Proper Soffet ventilation is essential to large amounts of incoming air needed for intake. Many attics were originally vented properly but have become packed with insulation along the way by an over-zealous insulation contractor or homeowner, in an attempt to actually stop air from coming in, sadly a common mistake. This mistake was very common in the 80's and 90's.
There are two basic types of Soffet vents: either a contiguous vent or a individual vents which come in round and square varieties. I generally prefer to use 6 inch by 12 inch square vents because of the ease of installation and the low material cost. They work surprisingly well and offer a lot of surface area. They can be purchased easily in brown white and silver to match virtually any siding.