Roof Vents Calculator

Intake & Exhaust Net Free Area Required

The Roof Vents Calculator computes the Net Free Area (NFA) of intake and exhaust ventilation required by IRC code for your attic. Standard rule: 1 sq ft of NFA per 150 sq ft of attic floor, split 50/50 between intake (soffit vents) and exhaust (ridge vents). Enter attic square footage and the tool returns the NFA needed plus the count of standard ridge and soffit vent pieces. Balanced ventilation prevents ice dams, mold, and premature shingle failure.