Attic Ventilation - Why It Is So Important

By Author: Ron Williams
Total Articles: 3
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.Every area of your home is effected by attic moisture, heat, and air flow.

Houses are built much "tighter" today than they were 20 or 30 years ago.

Windows are more efficient, house wraps are now commonly used, the R value of insulation has increased, overall, our homes are more weather-tight. In doing this we trap the moisture in the home. Indoor moisture is generated by many things. The normal perspiration and breathing of a family of four adds about ½ pint of water to the air every hour. Cooking three meals a day adds four or five pints of water to the air. Each shower contributes ½ pint. In fact, every activity that uses water, (like dishwashing, mopping floors, doing laundry) adds moisture to the air. Experts say that the daily living activities of a family of four can add more than 18 gallons of water a week into the air of a home. Air moisture will flow toward drier air to equalize itself. This equalization process actually forces the indoor moisture through the ceiling and insulation into the attic area.

The Benefits of Roof Ventilation

Allows outside air to flow naturally ...
... upward and out of attic.
Promotes a cooler, drier attic.
Helps prevent moisture from becoming trapped in insulation, structural wood, shingles and roof deck.
Helps prevent rotting, mildew, drywall damage, peeling paint and warped siding.
Provides year-round performance for consistent ventilation without energy consumption.

For a balanced ventilation system, you should have 50% of your NFV (net free ventilation) at the upper third of the roof and 50% at the lower third.

Balancing ventilation in this manner allows for air intake to occur at the low points and exhaust to take place at high points. Air movement from low to high points is aided by natural convection.

In attics which are not properly vented, moisture is also created by simple condensation. The air inside an improperly vented attic will be warmer than the air outside. When this warmer, moist air comes in contact with the colder roof sheathing condensation will occur. In effect, it can actually "rain" in your attic.
Ron Williams, "The Roof Doctor" has been involved in the Roofing Industry for over 38 years. Coming from a family of roofers, with two brothers, one a Sacramento roofing contractor, one a San Jose roofer, his father, and uncle all roofing contractors, Ron has developed a broad spectrum of roofing experience. The Roof Doctor has the knowledge to diagnose those tricky problems and get the job done right the first time.