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.
For the 1/150 attic ventilation requirement, simply double the amount of exhaust and intake calculated.
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 great introduction the art and science of choosing the right attic ventilation components for your roof.
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