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Ventilation

Attic ventilation might seem like a minor consideration, but when properly installed, it can extend the life of your attic and roof structure -- saving you hundreds of dollars in repair costs.

During warmer months, ventilation helps keep attics cool. It helps prevent hot, moist summer air from warping the roof sheathing. It also stops shingles from deteriorating prematurely. What's more, fresh air in the attic makes a home much easier to cool, which can result in lower energy costs.

In winter months, ventilation helps reduce moisture to keep attics dry. It stops water from backing up under shingles, damaging insulation, and rotting the roof structure itself. It also helps prevent ice dams from forming. Ice dams occur in areas where snowfall and cold temperatures are common and pose a special problem because they prevent melt water from running off the roof. They can even cause leaks inside your home, resulting in drywall damage. For more information on preventing ice dams, click here.

There are a number of variables to consider when selecting the most effective ventilation system for your home. Before you make any decisions, go up into your attic and take a look around. A sure sign of poor ventilation is an unbearably hot attic in the summer or frost on the nails in the winter. Another thing to check is evidence of moisture, such as mold, mildew, rusted nail heads, damp or compressed insulation and wood rot.

Once you've completed a general inspection of your attic, look for ventilation systems already in place, such as gabel vents or roof louvers. Note the size and location of each. Do the same with intake vents, including  soffit and eave vents.

Finally, make an estimate of the square footage of your attic. Most are slightly larger than the size of one floor of your home. You will need this figure to make sure you install adaquate ventilation. If your roof pitch is 7/12 to 10/20 add 20% to your calculation for vent requirements; 30% for roof pitches of 11/12 or steeper.

Vent Requirements
According to most building codes, you need one square foot of vent area for each 150 square feet of attic floor space. The minimum is one square foot for every 300 square feet of attic floor space if there is a vapor retarder or the space is balanced between the ridge and intake vents. A balanced ventilation system means about 50 percent of the required ventilating area should be provided by the exhaust vents in the upper portion of your attic with the remaining 50 percent provided by the intake vents. Please remember, building codes specify the minimum amount of ventilation. You may want to increase the requirement to ensure proper ventilation.

Common Mistakes
Too many times, homeowners install products that short-circuit their ventilation system. When designing a ventilation system, avoid these common mistakes:

  • Using a combination of different types of exhaust vents, like turbines and louver vents. In this case, competing vents pull air from each other instead of pulling air from the intake vents.
  • Underestimating your ventilation needs. Remember that 15 roof louvers or 5 turbine vents would be needed to provide the same ventilation as 42 feet of ridge vent on the same house
  • Installing exhaust vents without adequate intake. An effective balance of intake and exhaust must be acheived to properly ventilate your home. The flow of air in your attic is limited to the amount of intake air.

Additional Ventilation Information

All ventilation information has been provided by Air Vent Inc., for more information please visit www.airvent.com.

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