Site Fire Flow Analysis

Method

This tool implements IFC 2021 Appendix B Table B105.2 — required fire flow and duration for buildings other than one- and two-family dwellings, Group R-3 and R-4 buildings, and townhouses.

Lookup by construction group

Each row of Table B105.2 specifies a maximum fire-flow calculation area for each of five construction groups, mapped from IBC types per NFPA 220:

• Type IA & IB — non-combustible, fire-resistive (caps at 6,000 gpm)
• Type IIA & IIIA — protected non-combustible / protected ordinary (caps at 6,000 gpm)
• Type IV & V-A — heavy timber / protected wood frame
• Type IIB & IIIB — unprotected non-combustible / unprotected ordinary
• Type V-B — unprotected wood frame

Sprinkler reduction

When the building is sprinklered, the required fire flow is reduced to max(0.25 × required, floor) where the floor is 1,000 gpm for NFPA 13 systems and 1,500 gpm for NFPA 13R systems. The adjusted duration is then mapped from the adjusted flow rate:

• < 2,750 gpm → 2 hours
• 2,750–3,500 gpm → 3 hours
• ≥ 3,750 gpm → 4 hours

Floors used here are conservative and match the source spreadsheet. IFC 2021 B105.2 itself permits a 75% reduction with NFPA 13 to a minimum of 600 gpm. Confirm AHJ-accepted criteria before use.

Scope / exclusions

This tool does not apply to one- and two-family dwellings, Group R-3 and R-4 buildings, or townhouses (see IFC B105.1). For those occupancies the base requirement is generally 1,000 gpm for 1 hour (areas ≤ 3,600 sq ft), with reduction to 500 gpm permitted for NFPA 13D sprinklered buildings.