Choosing the Most Effective Roof Ventilation System for Your Structure
Intake and Exhaust
“Ventilate” comes from the Latin word for “to fan.” Simply put, it’s the action of moving air. Out with the hot. In with the cool. And that’s exactly how ventilation works. It provides conditions that allow air to flow. Every time stale, overheated air in your home or attic is vented out and fresh air is pulled in to replace it, you have what is known as an “air exchange.”
But ventilation is much more than a simple breeze blowing through your house. It’s a process that provides a steady, high volume of air movement. Think about it as a system of components, all sized and positioned to provide constant intake and exhaust of air.
Evaluate your needs.
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.
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.
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. In this case, competing vents pull air from each other instead of from soffit 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 achieved to properly ventilate your home. The flow of air in your attic is limited to the amount of intake.
Installing a ridge vent that doesn’t have an external baffle to increase air flow and protect from weather infiltration.