Daily Code Talk #34 — IMC 403 (Part 2): How to Use the Ventilation Table (403.3, 403.3.1, 403.3.1.1)

🧠 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.🧮 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).)🚧 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).🗺️ 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 TipIf 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.