Most industry authorities and Local Building Codes recommend a minimum of 1 sq. ft. (144 sq. in.) of Net Free Area (NFA) per 300 sq. ft. of attic floor space. This should be split evenly between intake and exhaust.
The SNOWVENTCO ventilation calculator will determine how much NFA is needed and how many roof vents are required based on this general rule. More ventilation area is preferred to less and you can not have too much ventilation or too many vents.
Step 1 – Determine Ventilation Area
Determine the square footage of the attic you wish to ventilate, or you can put the length and width of your attic space into our calculator to estimate the square footage of your attic.
Note: Be sure to factor the amount of soffit overhang into your calculation if applicable.
Step 2 – Calculate NFA Needed
Calculation is length X width / 300 * 144 = total NFA needed. This number should be split between intake and exhaust
Step 3 – Calculate Number of Vents Needed
Since all SNOWVENTCO vents are rated as 50 sq. in. of NFA, you will need to divide the number above by 50.
Half of the vents should be intake vents and half should be exhaust vents.
Other Calculation Considerations
The majority of roofs have soffit vents sufficient for attic intake ventilation. If your roof has soffit intake vents and they are functioning correctly, you will not need roof mounted intake vents.
When planning your roof ventilation needs, more ventilation is considered better than less.
The above NFA requirements are estimates and there is no need to follow the calculations exactly to ensure proper ventilation.