TL;DR
Net free area is the actual open area of a vent after subtracting louvers, screens, and grilles — the figure attic ventilation math uses rather than the vent's overall size. Codes require 1 square foot of it per 150 square feet of attic, reducible to 1:300 with balanced high and low vents, ideally split between ridge and soffit.
What it means
Net free area is the actual open area of a vent after subtracting louvers, screens, and grilles — the figure attic ventilation math uses rather than the vent's overall size. Codes require 1 square foot of it per 150 square feet of attic, reducible to 1:300 with balanced high and low vents, ideally split between ridge and soffit. Manufacturers stamp the rating on each product, and an attic that meets code on paper can still fail if insulation blocks the soffit openings.
Where it sits in the glossary
Net free area is part of the Trade jargon group inside the ProFix Directory glossary. Browse every term in this category from the glossary index.
Why Ohio homeowners should know it
This is a term Ohio homeowners encounter when reading contractor quotes, hiring paperwork, or inspection reports. Understanding it well enough to ask one good follow-up question is usually all the protection a homeowner needs.
ProFix Directory keeps definitions short on the index page and saves the longer context — Ohio-specific rules, where the term comes from, and which ProFix tools touch it — for these per-term pages so the term is easy to cite and easy to share.
ProFix tools that touch this term
See also
License: CC-BY-4.0 — quote freely with attribution to ProFix Editorial Team / ProFix Directory.