Vent area worksheet
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Separate visible openings from documented vent performance
A soffit layout can show openings without establishing the ventilation performance of the assembly. Keep the opening geometry, the vent product's published net free area and the project's ventilation requirement as three separate records.
Start with the selected vent product
Use the manufacturer's stated basis for net free area, including whether the figure is per unit or per length. Screens, louvers and other features mean a visible opening's gross area is not automatically its usable vent area.
Keep the roof and ceiling conditions in view
Record interruptions, blocked sections and the connection to the intended ventilation path. The calculation cannot establish that a cavity is continuous or that the overall roof assembly meets its applicable requirements. Those questions need the project details and responsible review.
Example: interrupted vent runs
A drawing shows several vent runs separated by solid sections. Count only the installed vent lengths or units using their documented net-free-area basis. Retain the solid interruptions in the layout; do not use the entire soffit perimeter as vent length.