Outdoor-Air Intake Location (401.4)
Plain English:
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): If a source is within 10 feet horizontally, place the intake not less than 3 feet below that source. 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.
On Plans: Why It Matters
Redlines here are siting errors: measured from the wrong street edge, missed the 25-foot vertical relief, intake set level with nearby exhausts, or intake below flood elevation. Resolve on the site plan before louvers are released.
🧾 Where To Show It (sheet map)
M-001: "OUTDOOR-AIR INTAKES PER IMC 401.4. SHOW OFFSETS TO LOT LINES, BUILDINGS, STREETS, ALLEYS, PARKING, LOADING, AND EXHAUSTS. WHEN FRONTING A STREET/PUBLIC WAY, MEASURE FROM THE NEAREST EDGE. IN FLOOD HAZARD AREAS, SET ABOVE IBC 1612."
M-101+: Dimension strings from each intake to lot line, on-site buildings, street/public way, parking/loading, and to nearest exhaust/plumbing vent; show vertical offsets where using the 25-foot allowance; draw flood design elevation.
M-501/502: OA louver detail (drainable section, screen, flashing continuity) with MI page; note vertical-offset logic and street-front measurement; cut a flood line through the wall section.
M-601 (Schedule adds): Intake ID | Serving System | Dist. to Lot Line | Dist. to Building | Dist. to Street/Public Way | Dist. to Parking/Loading | Nearest Exhaust/Plumbing Vent (H/V) | Intake Elev. & Flood Check | Louver Model + AMCA ref | MI Page.
Code Path: Zone-by-Zone Ventilation Schedule
Drawings must show the outdoor air rate for each occupancy zone, the recirculation rate (if any), and occupancy-specific requirements from IMC 403 or ASHRAE 62.1/ASHRAE 170.
For projects with multiple occupancies (office, conference, storage, healthcare), the ventilation schedule must address each occupancy type separately - a blended or single-rate schedule will be flagged.
Healthcare occupancies must reference ASHRAE 170 on the ventilation schedule per IMC 407.
Check: Mixed-Occupancy Verification
Confirm the ventilation schedule breaks down each zone by occupancy type - the OA rate per person and per area varies significantly between office, conference, storage, and retail.
For tenant improvement projects: verify the existing system OA capacity can serve the new occupancy, or show the system upgrade to meet the new OA rate.
Healthcare, laboratory, and parking garage occupancies require specific standards - confirm ASHRAE 170, ASHRAE 62.1, or IMC 404 is referenced for those zones.
Review Risk:
Mixed-occupancy tenant improvement projects that apply the dominant occupancy rate to the entire floor are the most common 401.3 error - each zone needs its own OA rate confirmed.
Existing system OA capacity not confirmed against the new occupancy requirement is a common tenant improvement permit oversight.
Recirculation from high-contaminant-load spaces (printing, chemical storage, cooking) without addressing Table 403.3.1.1 recirc restrictions is a first-cycle comment.
Field Tip:
If you cannot keep 10 feet horizontally from streets/parking, raise the intake to not less than 25 feet above that surface and show the dimension.
When facing a street/public way, pull distance from the closest edge, not the centerline.
Keep the intake at least 3 feet below any exhaust located within 10 feet; avoid level terminations.
In mapped flood zones, set the intake above the required elevation or detail an approved protection method.
Masterbuild QA Lens
Intake location is reviewed against the site plan and the elevation - not just the mechanical floor plan. Confirm clearances from lot lines, buildings, and all contaminant sources (streets, alleys, parking, loading docks, exhaust terminations) are dimensioned on both views. Flood-hazard intake elevation must match the civil drawings. Reviewers use the site plan; make sure the information is there.
Drawing / Submittal Check
For 401.3-401.4 (ventilation for specific occupancies and recirculation): the drawings must show the outdoor air rate for each occupancy zone, the recirculation rate (if any), and any occupancy-specific requirements (hospitals, schools, parking garages). For projects with multiple occupancy types, a zone-by-zone ventilation schedule is required - a single design OA rate applied to a mixed-occupancy building is a common comment.
Common Review Risk
Mixed-occupancy ventilation errors are common on tenant improvement projects. The mechanical designer applies the dominant occupancy rate to the entire floor, but the tenant has a mix of office, conference, and storage - each with a different required OA rate. A zone-by-zone ventilation schedule is the only way to demonstrate compliance for a mixed-occupancy floor. A single design OA rate on a mixed-occupancy set is a comment.
When To Escalate
Escalate when the mixed-occupancy ventilation design produces an outdoor air rate that the existing air handling unit cannot deliver without a fan upgrade. Ventilation requirements that exceed the existing AHU capacity require either an AHU replacement, a supplemental outdoor air unit, or a redesign of the space program - all of which affect the project budget significantly.
Load Assumption Check
Ventilation air quantities established in 401 Part 2 must be carried forward consistently into the psychrometric analysis. Confirm that the OA CFM on the ventilation schedule matches the OA CFM used in the coil load calculation.
Special Exhaust Coordination
For specialty exhaust, start with the contaminant and source. Then confirm capture method, duct material, routing, discharge, separation, controls, and whether another consultant or AHJ review is required.