: How to Use the Ventilation Table (403.3, 403.3.1, 403.3.1.1)
Plain English: Plain English Highlights
Who uses what:
R-2/R-3/R-4 ≤ 3 stories → see section 403.3.2 (coming later).
All other buildings → section 403.3.1 + Table 403.3.1.1.
Basis of design: In each occupiable space, deliver minimum outdoor air to the breathing zone continuously while occupied.
How to read the table: Pick the occupancy, pull Rp (people outdoor airflow rate, cfm/person) and Ra (area outdoor airflow rate, cfm/ft²), and use the table's occupant density unless you have approved statistics.
Smoking assumption: Rates assume no smoking (except smoking lounges). If smoking is expected elsewhere, increase OA by engineering judgment.
Unlisted occupancies: Use the closest listed classification (density/activity/construction) or an approved engineering analysis.
Calculation Check: Quick Calc Path (zone-level)
Vbz (breathing-zone OA) = Rp × Pz + Ra × Az, where Pz is zone population (people) and Az is zone floor area (ft²).
(Next post: apply Ez (zone air distribution effectiveness) and roll up to system OA for single-zone, 100% OA, and multi-zone systems; compute Voz (zone outdoor airflow).)
Coordination Check: Frequent Redlines
Choosing the wrong occupancy (e.g., "office" vs "conference").
Using program headcount < table density without approved stats.
Diffuser layout that doesn't deliver to the breathing zone.
Missing footnotes that trigger exhaust/recirculation limits (Notes b/g reference 403.2.1).
Code Path: Where to Show It (sheet map)
M-001: "Ventilation per IMC 403.3.1.1; Table 403.3.1.1 rates; non-smoking basis; densities per table (or approved stats on file)."
M-601: For each zone: Occupancy, Rp, Ra, Pz, Az, Vbz (and placeholders for Ez, Voz for later parts).
Calcs Appendix: One-pager documenting occupancy selections and any alternate density approvals.
Field Tip: Field Tip
If you deviate from the table's occupant density, include a short memo (a signed RDP note or AHJ email) that cites the data source and approved density. Place it in the calcs appendix and reference it on M-001. Bringing this memo with every submittal/resubmittal prevents hold comments and review delays.
Comment "IMC403" for the Ventilation & Exhaust Kit (Vbz worksheet, density cross-walk, Note b/g quick guide).
DM "ADVISORY" for a fast ventilation compliance sweep before you submit.
Masterbuild QA Lens
Ventilation posts should translate code language into a permit-ready airflow story: occupancy, outdoor air quantity, intake location, exhaust relationship, controls, and any exception being used.
Drawing / Submittal Check
Verify the drawings show occupancy basis, ventilation method, outdoor air path, intake and exhaust separation, transfer air assumptions, controls, and schedule values that match the calculation.
Common Review Risk
The common review risk is an airflow value without a traceable basis. Another risk is showing outdoor air on a schedule while the plan, intake location, or control sequence tells a different story.
When To Escalate
Escalate for healthcare spaces, high-occupant-load areas, unusual contaminants, existing air handlers with unknown outside air capacity, or any project where pressure relationships matter.
Ventilation Coordination
For outdoor air and exhaust locations, confirm separation distances, source hazards, rain/weather exposure, maintenance access, and the control sequence that proves the intended airflow during operation.