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Ventilation Systems and Requirements

FHA minimum property standards state ventilation should be one square foot of ventilation for each 150 square feet of insulated attic surface area.

Added Costs? No more than 15-20.00 per linear foot in most cases!

Savings? Tremendous reduction in  Air Conditioning, much longer life cycle of the roof system. Prevention of damaging other critical areas of the attic, such as attic insulations and or framing due to trapped moisture

Roof ventilation in Texas has not been a standard business practice with the serious lack of over all quality control. With the added costs to properly install a venting system. Most Texans are not even being offered the Shingle Vent Systems today. Did you know that Manufacturer specifications these days specify using adequate ventilation systems?

What is attic ventilation? By AirVent ®

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.

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. 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.

Types of Vents

(Click here to learn about a variety of ventilation products from Air Vent.)

Roofing Ventilation Solutions by GAF: Why Use a System - Attic Ventilation

Proper attic ventilation is crucial for a long-lasting roofing system!
Select from the following topics to learn more:

  • Why attic ventilation is important
  • How to estimate your attic ventilation requirements
  • Select the right exhaust ventilation option
    (ridge vents, power vents, louvers, turbines... see chart below)
  • View additional products
    Chimney / Roof Caps & Other Accessories
    Gable Louver (Intake/Exhaust)
    Soffit/ Undereave Vents (Intake)
  • How to save energy by installing a whole house fan

Check out the latest ventilation products
by GAF

• Snow Country Advanced™
• Cobra® Rigid Vents™
• Cobra® Ridge Runner™
• MasterFlow® Intake Booster
• MasterFlow® Exhaust Vent



Calculating Your Ventilation Requirements
Example: Calculating the number of lineal feet of Cobra® Exhaust Vent needed for a 30’x 40’ attic:

Step 1

Step 2

Step 3

Step 4


Step 5




Calculate attic square footage
How: Multiply length of attic (in feet) times width of attic (in feet)
30’ x 40’ = 1,200 square feet

Calculate NFA (Net Free Area) needed for this attic by using the “1 in 300” rule
How: Divide attic square footage by 300
1,200 sq. ft. ÷ 300 = 4 square feet of NFA needed

Convert square feet of NFA to square inches

How: Multiply square feet of NFA by 144
4 sq. ft. x 144 = 576 square inches of NFA needed

Split the amount of NFA needed equally between the intake and the exhaust
How: Divide square inches of NFA needed by 2
576 sq. in. ÷ 2 = 288 square inches of NFA needed equally for exhaust & intake

Calculate # of lineal feet of Cobra® Exhaust Vent needed
How: Divide the square inches of NFA needed at the ridge by the NFA of the Cobra® Exhaust Vent
(Cobra® Exhaust Vent has 16.9 sq. inches of NFA per lineal foot)
288 sq. in. ÷ 16.9 = 17 lineal feet

This attic requires seventeen (17) lineal feet of Cobra® Exhaust Vent to meet FHA minimum requirements.

Intake ventilation MUST be at least equal to exhaust ventilation. To determine the number of intake vents needed, select your vent on page 12, and install enough vents so that their combined NFA is at least 288 square inches.

have a balanced ventilation
system. In no case should the amount of exhaust ventilation exceed the amount of intake


If you have needs for a truly Qualified Contractor in the Dallas Ft-Worth area. Please don't hesitate to CONTACT US for your free consultation and evaluation.






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