Attic Ventilation Calculator
How to Calculate
Measure the length and width of the attic floor space to be ventilated.
Enter the length and width or the total square footage of the attic floor space to be ventilated.
See recommended quantities below for each GAF Ventilation Product (typically rounded up).
Use this calculator to help determine the proper amount of attic ventilation based on U.S. FHA 1/300 guidelines.*
Suggestions for ' x ' Area
Suggestions for sq. ft. Area
Numbers shown represent the recommended total number of units required for a single product.
384 Minimum Sq. In. of Net Free Area of exhaust needed at or near the ridge.
384 Minimum Sq. In. of Net Free Area of intake needed at or near the soffit.
Some local building codes require the 1/150 attic ventilation rule, which increases the minimum attic ventilation needed. Always consult local building code requirements in your area for details.
Note: N/R = not recommended
cobra® & truslate® plastic vents (Lineal Feet)
Cobra® Exhaust Vent - Mesh Rolls (Lineal Feet)
Master Flow® Aluminum Ridge Vent (Lineal Feet)
Master Flow® Roof Louvers (# of Vents)
Cobra® Intake Vents (Lineal Feet)
Master Flow® Soffit/Undereave Vents (# of Vents, except for LSV8)
Intake or Exhaust Ventilation
Note: Gable louvers are typically installed in pairs
Master Flow® Metal Gable Louvers (# of Vents)
MasterFlow® Plastic Gable Louvers (# of Vents)
MasterFlow® Plastic Circular Louvers (# of Vents)
Master Flow® Power Attic Vents - Roof Mount (# of Vents)
Master Flow® Power Attic Vents - Gable Mount (# of Vents)
Master Flow® Green Machine™ Solar Vents (# of Vents)
Master Flow® Wind Turbines (# of Vents)
Cobra IntakePro® (Lineal Feet)
LSV8 Metal Continuous Soffit Vents (Lineal Feet)
EAP 4x12 Plastic Soffit Vents (# Of Vents)
EAC 16x4 Metal Soffit Vents (# Of Vents)
EAC 16x8 Metal Soffit Vents (# Of Vents)
EmberShield® Closeable Soffit Vents (# Of Vents)
The 1/300 Balanced Attic Ventilation RuleProper attic ventilation consists of a balance between air intake (at or near your soffits) and air exhaust (at or near your roof ridge). The U.S. Federal Housing authority recommends a minimum of 1 square foot of attic ventilation (evenly split between intake and exhaust) for every 300 square feet of attic floor space. Always have a balanced ventilation system. In no case should the amount of exhaust ventilation exceed the amount of intake ventilation.
*Note: The 1/300 rule is a general rule and does not apply to all situations. Local building codes, when stricter, take precedence. Always consult a design professional for cathedral ceilings, insulated roof decks, etc.
Learn About Attic Vent OptionsAre you confused about the many attic ventilation solutions available? Curious why one roof would get ridge ventilation and another would incorporate power vents or a roof louver? Watch this video for a great introduction to the art and science of choosing the right attic ventilation components for your roof.
Your Top Attic Ventilation Questions Answered
Among the potential issues homeowners need to deal with in colder weather, few are quite as troublesome as ice dams. When winter arrives, the roof is a home's first line of defense against nature. Changing temperatures can force water to inconsistently melt and freeze once more, causing water leaks and icy blockages that may be responsible for causing damage to roof shingles, wood decking, gutters, and insulation down the line.
By Mark Soto
Your attic needs to breathe. Poor ventilation may lead to excess heat and moisture and potential roof system degradation. The attic ventilation options that are best for your home will vary based on the style of your roof to ensure that each attic space has a balanced system for intake and exhaust. Balanced systems need to draw in fresh air and export hot, moist air.
A balanced attic ventilation system helps reduce damaging heat and moisture in attic spaces, which may help reduce the load on air conditioning systems and lower the risk of ice dam formation in the winter.
When considering replacing your roof, you'll need to calculate the amount of attic ventilation needed to help reduce excess heat and moisture in your attic. Excess heat and moisture can lead to premature roof system degradation and damaging ice dams in the winter.