IMC 2024 Ch4: Section 401 — ventilation required where natural ventilation per IBC 1203 is not provided. Section 403 — outdoor air: ASHRAE 62.1 rates. Office: 5 cfm/person + 0.06 cfm/sf. Classroom: 10 cfm/person + 0.12 cfm/sf. Retail: 7.5 cfm/person + 0.06 cfm/sf. Section 401.3 — economizer required per IECC when applicable. Section 502 — exhaust rates: commercial kitchen Type I hood (400 cfm/linear ft min), bathrooms (50 cfm intermittent or 20 cfm continuous), parking garages (0.75 cfm/sf). Section 504 — duct systems: materials per UL 181/181A/181B, support at intervals per material type, fire dampers at rated assemblies. Section 505 — return air: not from hazardous, toilet, kitchen, storage, or parking areas.