“A-1” Occupancy Corridor Width – Application of Universal Design

General Definition

The Common Path of Travel refers to the portion of the exit access that occupants must traverse before they have the option to choose between two independent exit paths.
- Under the Building Standard Law of Japan (BSL), common path of travel is defined similarly as the initial travel distance before reaching a point where two distinct exit routes become available. However, BSL regulations offer a more context-specific and flexible approach to defining maximum common path distances, depending on:
  - The number of floors in the building.
  - The presence of fire-resistant walls and sprinkler systems.
  - Occupancy type and size of the assembly area.

The corridor width requirements for Group A-1 occupancy (assembly use) are specified in
- IBC (USA): Section 1020.2, which outlines minimum corridor widths based on occupant load and use.
- BSL (Japan): Article 119, which provides fixed minimum corridor widths for different building types, including assembly spaces.

Code	Corridor Width Requirement for A-1 Occupancy
IBC (Section 1020.2 – USA)	– Minimum 44 inches (1118 mm) for occupant load ≥50. – Minimum 36 inches (914 mm) for occupant load ≤50. – Corridor width must increase based on required egress width calculations.
BSL (Article 119 – Japan)	– Minimum 90 cm (35.4 inches) for general corridors. – Minimum 120 cm (47.2 inches) for large assembly buildings and high-density occupancy.

IBC requires wider corridors (44 inches / 1118 mm) for high occupancy (>50 people), while BSL allows 90 cm (35.4 inches) minimum for general corridors.
BSL requires a wider corridor (120 cm / 47.2 inches) for large assembly buildings, making it comparable to IBC’s requirements for high-density spaces.
IBC uses a more dynamic approach, requiring corridor width to be calculated based on occupant load, whereas BSL enforces fixed minimum widths.

Code	Impact of Fire Protection Features	Impact of High-Density Occupancy
IBC (1020.2)	– Corridor width cannot be reduced even if the building is sprinklered. – Minimum clear width must be maintained regardless of fire protection.	– Occupant load determines corridor width, requiring larger corridors in assembly spaces.
BSL (Article 119)	– Sprinklered buildings may use the 90 cm minimum width in some cases.	– Corridor width increases to 120 cm (47.2 inches) for large assembly halls and high-density spaces.

IBC corridor widths remain fixed regardless of fire protection, while BSL allows narrower corridors in sprinklered buildings.
Both codes require wider corridors for high-density occupancies, but IBC calculates the width based on actual occupant load, while BSL sets a fixed 120 cm (47.2 inches) minimum for large assembly buildings.

Code	Accessibility & ADA Compliance	Emergency Egress Considerations
IBC (1020.2)	– Corridor widths must accommodate wheelchair access (minimum 36 inches / 914 mm in some cases). – Increased corridor widths required for accessibility in public buildings.	– Corridors must allow safe and rapid evacuation, with clear egress paths. – Fire-rated corridors may require wider widths depending on egress demand.
BSL (Article 119)	– Corridors must comply with Japanese accessibility standards but do not follow ADA-specific measurements. – 90 cm minimum may not always accommodate wheelchair users easily.	– Fire protection and egress studies determine if corridor width needs to be expanded beyond the fixed 90 cm or 120 cm standards.

IBC explicitly accounts for accessibility (ADA compliance), ensuring that corridors accommodate wheelchair users, whereas BSL has different accessibility provisions that do not necessarily align with ADA standards.
IBC allows for dynamic corridor width increases based on egress demand, whereas BSL uses fire safety evaluations to determine width adjustments.

Aspect	IBC (1020.2 – USA)	BSL (Article 119 – Japan)
Minimum Corridor Width	44 inches (1118 mm) for >50 occupants. 36 inches (914 mm) for ≤50 occupants.	90 cm (35.4 inches) minimum. 120 cm (47.2 inches) for large assembly buildings.
Width Calculation	Based on occupant load and egress demand.	Fixed minimums (90 cm or 120 cm).
Fire Protection Impact	No width reduction for sprinklered buildings.	May allow 90 cm corridors in sprinklered buildings.
Accessibility	Explicit ADA compliance required (wheelchair access ensured).	General accessibility standards apply, but no ADA-specific regulations.
Emergency Egress Considerations	Corridors must ensure rapid evacuation based on dynamic egress calculations.	Width adjustments may be required based on fire safety studies.

Issue	IBC Recommendation	BSL Recommendation
Minimum Corridor Width for Assembly Spaces	Increase minimum corridor width to 48 inches (1220 mm) for A-1 occupancies to match global best practices.	Increase 90 cm minimum to 100 cm (39.4 inches) for better evacuation efficiency.
Corridor Width Flexibility	Allow some flexibility for width reductions in low-density areas if fire protection features are present.	Introduce occupant-based corridor width calculations for large assemblies, instead of using fixed 120 cm.
Accessibility Improvements	Ensure all corridors meet universal design principles (beyond ADA compliance).	Standardize wheelchair-friendly corridor dimensions across all public spaces.

IBC requires wider corridors (44 inches / 1118 mm) compared to BSL’s 90 cm (35.4 inches) for general corridors.
BSL mandates a 120 cm (47.2 inches) corridor width in large assembly buildings, which is comparable to IBC’s high-occupancy standards.
IBC uses occupant-load-based width calculations, whereas BSL enforces fixed width minimums.
BSL allows 90 cm corridors in some sprinklered buildings, while IBC maintains strict width requirements regardless of fire protection.
IBC explicitly integrates ADA accessibility compliance, whereas BSL follows separate accessibility standards that do not fully align with ADA guidelines.
IBC is more adaptable for emergency egress based on actual building use, whereas BSL relies on fixed fire safety assessments for width adjustments.