Glossary / net free area

net free area

The unobstructed opening area a vent still provides after mesh or a listed core. Fine mesh reduces it. Size vents so the attic still meets ventilation code.

Last verified 2026-08-23. JSON (CC BY 4.0)

Also called: NFA.

Related

• mesh
• listed
• vents
• Mesh versus listed vents
• Net free area after mesh or a listed core

Where this term is used

7 guides use this term.

• Bird blocks, boxed soffit, or unvented attic
• Mesh versus listed vents
• Net free area after mesh or a listed core
• OSFM 8165 vent applications
• Ridge vents versus ASTM E2886
• The 12-foot rule
• Unvented attic as a wildfire path