IMC · 2021 International Mechanical Code

§402.1 · Natural ventilation

Effective in IMC 2021 · IMC 2024 SE Wisconsin · IMC 2024 NW Indiana.

Plain-English explainer

402.1 lets a space labeled 'naturally ventilated' meet the rate with operable openings sized at ≥4% of the floor area. The drafter cites it when a basement or attic conversion is relying on openable windows instead of a mechanical supply.

Why inspectors flag this

A bedroom or office below grade that claims natural ventilation almost always fails unless the window area demonstrably exceeds 4%; surfacing this on the draft forces the call before the rough-in walk-through.

As quoted in the code: Spaces labeled "naturally ventilated" need operable openings sized at no less than four percent of the floor area served.

See all codes that cite this trade

Browse the full International Mechanical Code index for one place to read every section the drafter is allowed to quote. See all codes →

See pricing

See every code, every jurisdiction — without the binder.

Trussmark turns job-site photos and voice notes into code-cited permit drafts the inspector can verify on the spot. Pick the plan that fits your shop and we will size the rest with you. Already cited this code in IMC 2021? Drop your email and we'll size the rest of the permit draft for you. See pricing →

See pricing