IMC · 2021 International Mechanical Code

§401.2 · Outdoor air

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

Plain-English explainer

401.2 requires every occupiable space to be supplied with outdoor air at the rate set in Table 403.3.1.1, either through a natural opening or a mechanical system. The drafter cites it when a permit pulls in a fresh-air duct, HRV, or makeup-air run sized to the space type.

Why inspectors flag this

Inspectors read 401.2 as the umbrella rule for the rest of Chapter 4 — failing it means every downstream exhaust problem is also a finding.

As quoted in the code: Every occupiable space must be supplied with outdoor air by a natural opening or a mechanical system at the rate set in Table 403.3.1.1 (or an equivalent the jurisdiction has approved).

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