/ Field knowledge · IMC 401.4
Measure from the nearest edge, not the centerline.
IMC 401.4: measure from the nearest edge of the street, not the centerline. For a street, alley, parking, or loading surface within the 10-ft horizontal offset, §401.4 allows an intake at least 25 ft above that surface. This is not a 25-ft alternative for plumbing vents or other exhaust. For a contaminant source within 10 ft horizontally, separately evaluate the at-least-3-ft-below-source path.
Educational 2024 IMC 401.4. Confirm adopted edition. Distinct from Type II exhaust 3-10-10-10-30 on 506.4, 501 discharge, and 401.5 screens / AMCA 550. This is not a louver selection. Packet: 401.4 PDF · ES.
- 401.4(1): intakes not less than 10 feet from lot lines and from other buildings on the same lot.
- 401.4(2): keep not less than 10 feet horizontally from contaminant sources (vents, streets, alleys, parking, loading). You may be closer to streets/alleys/parking/loading only when the intake is not less than 25 feet above those surfaces. If fronting a street/public way, measure from the nearest edge.
- 401.4(3): for a contaminant source within 10 feet horizontally, the separate vertical path places the intake not less than 3 feet below that source; document both dimensions and source type. Exception: no separation needed for an individual dwelling unit using a listed combo intake-exhaust fitting installed per the fan manufacturer.
- 401.4(4): in flood hazard areas, set intakes at or above the elevation required for utilities and attendant equipment by IBC 1612.
Put dimension strings on the site plan and the elevation. Mixed-occupancy TI that applies one OA rate to the whole floor is a 401.3 comment — each zone needs its own rate — but the louver still has to sit where 401.4 allows it.
Measured from the centerline
Wrong street edge, applying the 25-ft option to a vent/exhaust rather than a street/alley/parking/loading surface, missing the 3-ft-below check at a nearby source, or intake below flood elevation. Resolve on the site plan before louvers are released.
Source: 2024 IMC §401.4 · DCT 401.4 · tool: intake screen · ventilation: 403 · natural: 401 natural.
What to send
The site plan, intake elevation, and distances to streets, parking, exhausts, and lot lines.
If the OA louver faces the street
Send the site plan. MasterBuild will say whether 401.4 even clears 10 / 25 / 3 — or the louver has to move before it is released.
Send Project Background+1 (786) 398-6940 · osmany.portal@masterbuildconsulting.com
MasterBuild provides engineering services under a written scope. Nothing on this page is project-specific engineering advice, a code interpretation for your project, or a representation about permit approval. Confirm the adopted edition. Distances below are 2024 IMC / 2026 NEC model-code education from Daily Code Talk.