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Incidental Use

General Definition

  • Incidental Use refers to secondary spaces within a primary occupancy that pose an increased fire or life safety risk and require additional protection.
    • These spaces are not large enough to be considered separate occupancies but require specific fire-resistant construction, sprinkler systems, or smoke control measures.
      • Both the International Building Code (IBC) and Japan’s Building Standard Law (BSL) recognize incidental uses, but BSL enforces stricter fireproofing (耐火建築物), seismic stability, and compartmentalization for hazardous or high-risk spaces.

IBC Classification & Requirements for Incidental Use

  • The IBC (International Building Code) defines Incidental Use Areas as spaces that:
    • Are accessory to the primary occupancy
    • Increase fire or life safety risk
    • Require fire-resistance-rated separation, fire sprinklers, or smoke control

Common Examples of Incidental Use Areas under the IBC

  1. Mechanical & Boiler Rooms – Spaces containing fuel-fired equipment or HVAC systems.
  2. Storage Rooms (Over 100 sq. ft.) – Rooms storing flammable or combustible materials.
  3. Laundry Rooms (Over 100 sq. ft.) – Areas with commercial laundry equipment.
  4. Chemical Laboratories in Educational Buildings – Laboratories using small amounts of hazardous materials.
  5. Parking Garages & Enclosed Vehicle Storage – Enclosed areas used for storing vehicles within another occupancy.

IBC Requirements for Incidental Use Areas

  • Fire-Resistance Rating: Typically, 1-hour fire-rated separation from the main occupancy.
  • Fire Sprinklers: May be required if fire-rated separation is not provided.
  • Smoke Control & Ventilation: Required in certain cases (e.g., chemical storage, parking garages).

BSL Classification & Requirements for Incidental Use

(附属建築物 – Fuzoku Kenchikubutsu & 特殊用途室 – Tokushu Yōto Shitsu)

  • The Building Standard Law of Japan (BSL) classifies Incidental Use Areas under:
    • 附属建築物 (Fuzoku Kenchikubutsu) – Accessory Buildings – Small detached structures that support a primary building.
    • 特殊用途室 (Tokushu Yōto Shitsu) – Special-Use Rooms – High-risk rooms inside a primary occupancy that require additional fire protection.

    Common Examples of Incidental Use Areas under the BSL:

    1. 機械室 (Kikaishitsu) – Mechanical & Boiler Rooms – Fuel-fired equipment spaces requiring fireproofing and ventilation.
    2. 倉庫 (Sōko) – Storage Rooms – Storage spaces over 100 m² (1,076 sq. ft.) requiring fire-rated compartments.
    3. 洗濯室 (Sentakushitsu) – Laundry Rooms – Large commercial laundry rooms requiring fire barriers.
    4. 研究室 (Kenkyūshitsu) – Laboratories in Schools – School science labs handling flammable or hazardous chemicals.
    5. 駐車場 (Chūshajō) – Enclosed Parking Garages – Underground and enclosed parking areas requiring fireproofing and ventilation.

    BSL Requirements for Incidental Use Areas:

    • 耐火建築物 (Fireproof Construction): Mandatory for rooms storing flammable materials or hazardous substances.
    • Fire Sprinklers: Required in storage rooms over 100 m² and underground parking garages.
    • Compartmentalization & Smoke Control: Mandatory for enclosed spaces with fire risk (e.g., mechanical rooms, laboratories).

    Key Differences:

    • BSL regulates incidental use spaces more strictly, requiring larger storage rooms and parking garages to have fireproofing and compartmentalization.
    • IBC allows more flexibility in using sprinklers instead of fire-rated separation, while BSL often mandates both.
    • Seismic design is a stronger requirement in BSL, especially for mechanical rooms and storage areas with hazardous contents.

    IBC vs. BSL – Summary of Incidental Use Requirements

    Incidental Use TypeIBC (Incidental Use Areas)BSL (附属建築物 & 特殊用途室 – Accessory & Special-Use Rooms)
    Mechanical & Boiler Rooms1-hour fire-rated separation or sprinklers耐火建築物 (Fireproof Construction) required
    Storage Rooms (>100 sq. ft./9.3 m²)1-hour separation or sprinklersFireproofing required for rooms >100 m²
    Laundry Rooms (>100 sq. ft./9.3 m²)Fire-rated separation requiredMust have fire-rated walls & exhaust systems
    Educational Science LaboratoriesFire-rated separation for flammable chemicalsFireproofing & smoke control required
    Enclosed Parking GaragesFire-rated separation & ventilation requiredMandatory fireproofing & sprinklers for underground garages

    Summary

    • IBC recognizes incidental use areas but provides more flexibility in fire protection through fire-rated separation or sprinklers.
    • BSL enforces stricter fireproofing and compartmentalization for high-risk spaces, especially in storage, mechanical rooms, and underground garages.
    • Seismic stability requirements in BSL are stricter for incidental use areas, particularly mechanical rooms and hazardous material storage.
    • Both codes prioritize fire safety and smoke control, but BSL requires a greater level of fire-resistant construction.