ibc-building-codes

Overview

Structured reference for the US International Building Code (IBC) 2021 and International Residential Code (IRC). Use it to validate building designs, generate code-compliant models, and understand occupancy and construction type constraints. Covers common residential and mixed-use scenarios including occupancy classifications, construction types, height/area limits, egress requirements, and sprinkler systems.

Instructions

Occupancy Classifications (IBC Chapter 3)

• A -- Assembly: A-1 (theaters), A-2 (restaurants/bars), A-3 (libraries/gyms), A-4 (indoor arenas), A-5 (outdoor stadiums)
• B -- Business: offices, banks, outpatient clinics
• E -- Educational: K-12 schools, day care (>5 children)
• F -- Factory: F-1 (moderate hazard), F-2 (low hazard)
• H -- High Hazard: H-1 through H-5
• I -- Institutional: I-1 (supervised residential), I-2 (hospitals), I-3 (jails), I-4 (day care)
• M -- Mercantile: retail stores, markets
• R -- Residential: R-1 (hotels, <30 days), R-2 (apartments/condos), R-3 (single-family), R-4 (assisted living 6-16)
• S -- Storage: S-1 (moderate hazard), S-2 (low hazard)
• U -- Utility: garages, fences, tanks

Construction Types (IBC Table 601)

• Type I (non-combustible, highest fire resistance): I-A (unlimited height/area), I-B (unlimited)
• Type II (non-combustible, lower rating): II-A (1 hr), II-B (0 hr)
• Type III (non-combustible exterior, combustible interior): III-A (1 hr interior), III-B (0 hr)
• Type IV (heavy timber/mass timber): IV-HT, IV-A, IV-B, IV-C
• Type V (combustible/wood frame): V-A (1 hr, protected), V-B (0 hr, unprotected)

R-2 Height and Story Limits

Without sprinklers / With NFPA 13 sprinklers (+1 story, +20 ft):

Egress Requirements (IBC Chapter 10)

• Travel distance (R-2): 125 ft (38 m) -- not increased with sprinklers
• Exit access doorways: 2 required if unit > 500 SF; 1 permitted if unit <= 500 SF
• Stairway width: 44" (>49 occupants), 36" (<=49 occupants)
• Corridor width: 44" minimum for common corridors
• Riser height: 4"-7" (7-3/4" max residential); Tread depth: 11" minimum

Occupant Load (IBC Table 1004.5)

• R-2 Residential: 200 SF gross per occupant (round up)
• Example: 834 SF / 200 = 4.17 -> 5 occupants
• Assembly (no fixed seats): 7 SF net per person
• Business: 100 SF gross per person

Sprinkler Systems

• NFPA 13 -- Full coverage including concealed spaces; required for R-2 > 4 stories; enables +1 story/+20 ft
• NFPA 13R -- Residential up to 4 stories; covers units and corridors; same height increase as NFPA 13
• NFPA 13D -- One/two-family dwellings only (R-3); does not trigger IBC height increases

R-2 Dwelling Unit Minimums (IBC Section 1208)

• Ceiling height: 7'-0" habitable rooms, 6'-8" bathrooms/corridors
• Studio/efficiency: 220 SF minimum
• Sleeping rooms: 70 SF minimum, 7'-0" minimum dimension
• Corridor within unit: 36" minimum; common corridor: 44" (>= 50 occupants)

Examples

Example 1: Checking Occupancy Classification

A developer is designing a mixed-use building with apartments on floors 2-4 and a restaurant on the ground floor. They need to determine the correct IBC occupancy classifications.

Building use analysis:
  Floors 2-4: 12 apartment units (permanent residents, lease > 30 days)
    -> R-2 (Multi-family residential, permanent occupancy)
  Floor 1: Restaurant with bar seating for 120 patrons
    -> A-2 (Assembly, food/drink consumption)

Result: Mixed occupancy R-2 / A-2
  - Must meet the more restrictive requirements of both occupancy types
  - Fire separation required between A-2 ground floor and R-2 upper floors (IBC Table 508.4)
  - Sprinkler system: NFPA 13 recommended (covers both occupancies)

Example 2: Validating Egress Requirements

An architect needs to verify that a 3-story V-B apartment building with NFPA 13 sprinklers meets IBC egress requirements.

Building: R-2, V-B, 3 stories, NFPA 13
  Unit sizes: Type A = 834 SF, Type B = 645 SF (6 of each per floor)

Height/story check:
  Permitted: 4 stories / 60 ft (V-B + NFPA 13)
  Actual: 3 stories / 35 ft
  -> PASS

Travel distance check:
  Maximum permitted: 125 ft (R-2, not increased with sprinklers)
  Actual longest path: 66 ft (Level 2, far unit to nearest stair)
  -> PASS

Exit access doorways:
  Type A (834 SF > 500 SF): 2 exit access doorways required -> PASS (has 2)
  Type B (645 SF > 500 SF): 2 exit access doorways required -> PASS (has 2)

Stair width:
  Occupant load per floor: (6 x 5) + (6 x 4) = 54 occupants
  54 > 49 -> 44" minimum stair width required
  Actual: 44" -> PASS

Overall: ALL EGRESS REQUIREMENTS MET

Guidelines

• IBC 2021 is the reference edition; local jurisdictions may adopt older editions or amendments
• Always verify against the locally adopted code -- many cities add amendments (e.g., NYC, Chicago, LA)
• Height/area increases from sprinklers apply only once, regardless of sprinkler type (NFPA 13 vs 13R)
• Mixed-occupancy buildings must meet the more restrictive requirements of all occupancy types present
• Occupant load calculations always round up to the next whole number
• This reference covers common scenarios; unusual occupancy types (H, I) require specialist review
• The data here is for reference and education -- not a substitute for a licensed code official's review