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. Another thing to check is evidence of moisture, such as mold, mildew, rusted nail heads, damp or compressed insulation or wood rot.
Once you've completed a general inspection of your attic, look for ventilation systems already in place, such as gable vents or roof louvers. Note the size and locations 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 in your home. You'll need this figure to make sure you install adequate ventilation.
If your roof pitch is 7/12 to 10/12, plan to add 20% to your calculation for vent requirements; 30% for roof pitches of 11/12 and 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 exhaust vents in the upper portion of your attic with the remaining 50 percent provided by 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 pitfalls
- Using a combination of different types of exhaust vents, like power vents with ridge vents.
- Underestimating your ventilation needs. Remember that 15 roof louvers or 5 turbine vents would be needed to provide the same ventilation ast 42 feet of ridge vent on the same house.
- Installing exhaust vents without adequate intake. An effective balance of intake and exhaust must be achieved to properly ventilate your home. The flow of air in your attic is limited to the amount of intake.
