Enter the total attic floor space (ft^2) into the Calculator. The calculator will evaluate the Net Free Air. 

Net Free Air Formula

NFA = FP/150


  • NFA is the Net Free Air (ft^2)
  • FP is the total attic floor space (ft^2)

To calculate Net Free Air, divide the total attic floor space in square feet by 150.

How to Calculate Net Free Air?

The following steps outline how to calculate the Net Free Air.

  1. First, determine the total attic floor space (ft^2). 
  2. Next, gather the formula from above = NFA = FP/150.
  3. Finally, calculate the Net Free Air.
  4. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

total attic floor space (ft^2) = 600

Frequently Asked Questions (FAQ)

What is Net Free Air?

Net Free Air (NFA) refers to the amount of open area, measured in square feet, required for adequate ventilation in an attic space. It is a crucial factor in ensuring proper air flow to prevent issues like moisture accumulation and to maintain energy efficiency.

Why is calculating Net Free Air important?

Calculating the NFA is important for maintaining the structural integrity of a building, preventing mold growth, and ensuring the efficiency of heating and cooling systems. Proper attic ventilation can also extend the life of roofing materials by reducing temperature extremes.

How does attic floor space affect the Net Free Air calculation?

The total attic floor space directly impacts the NFA calculation since the NFA is determined by dividing the attic floor space by 150. This means the larger the attic floor space, the greater the required Net Free Air for adequate ventilation.

Can the Net Free Air formula be used for any attic size?

Yes, the NFA formula (NFA = FP/150) is a general guideline that can be applied to any attic size. However, specific building codes and climate considerations may necessitate adjustments to ensure optimal ventilation for different attic configurations and sizes.