What are the key changes in Chapter 2 Definitions of CBC 2025?

Chapter 2 sees one of the largest expansions of new definitions, especially around:

• Lithium-ion battery hazards
• Roof slope terminology
• IT spaces (Computer Room vs. Data Center)
• Temporary structures, peer review
• Fire extinguishing systems
• Modern cladding materials (IMP, insulated vinyl siding)
• Occupiable roofs
• Metal building systems

These definitions drive major downstream effects across fire protection, construction types, and building envelope chapters.

Full Detailed Table of All Changes  -  Chapter 2

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FAQs

1. Why did CBC 2025 add so many new definitions in Chapter 2?

Because modern construction practices, materials, and technology have evolved rapidly. The 2025 update aligns the code with current industry realities—from lithium-ion battery hazards and photovoltaic systems to new envelope materials, data centers, and temporary structures.

2. Do these definition changes affect actual design requirements?

Yes. Definitions are no longer just vocabulary—they determine when and how specific chapters apply. Many fire protection, egress, envelope, and structural requirements now hinge on whether a space or material matches these new definitions.

3. What’s the significance of the new IT space definitions (Computer Room, Data Center, ITE)?

These definitions separate low-power IT rooms from high-capacity data centers. The distinction controls sprinklers, smoke detection, suppression systems, and egress requirements, especially for buildings with significant digital infrastructure.

4. Why are roof slope definitions important (low-slope vs. steep-slope)?

Roof slope now formally determines:

• roofing system classification
  
• drainage and overflow design
  
• fire ratings
  
• weatherproofing and WRB requirements
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This eliminates ambiguity in Chapters 7, 9, 14, and 15.

5. How do new definitions impact exterior wall and cladding systems?

Definitions for Insulated Metal Panels (IMP), Insulated Vinyl Siding, and BIPV ensure proper fire testing, WRB performance, installation standards, and envelope continuity. These changes coordinate major upgrades in Chapter 14.

6. Why are temporary structure definitions expanded?

CBC now distinguishes between Temporary Structures, Public-Occupancy Temporary Structures, Temporary Events, and Service Life. This gives AHJs clearer authority to regulate pop-ups, events, festival structures, and long-term “temporary” installations.

7. What does the new “Occupiable Roof” definition change?

It determines which roofs require:

• guardrails
  
• emergency egress routes
  
• occupant load calculations
  
• fire protection requirements
  

Any roof intended for human presence must now meet expanded criteria.

8. How does the “Metal Building System” definition affect structural design?

It formally recognizes pre-engineered metal buildings and ties them to new requirements for:

• fire-resistance continuity
  
• structural performance
  
• wall/roof interface detailing
  

This impacts both compliance and documentation.

9. Why is “Peer Review” now defined?

To support Chapter 1’s granting of authority to AHJs to mandate third-party review for complex or high-risk buildings. The definition ensures consistency in how peer review is interpreted, performed, and enforced.

10. What’s the impact of definitions related to lithium-ion hazards?

They establish baseline terminology for high-risk battery storage and charging environments. This affects fire-resistance ratings, ventilation, detection, and separation requirements in multiple chapters.

11. How will these new definitions affect plan checks and inspections?

Expect more code officials to ask:

• “Is this space a Data Center or Computer Room?”
  
• “Does this roof qualify as occupiable?”
  
• “Does this cladding meet the IMP definition?”
  
• “Is peer review required for this system?”
  

These definitions now control the triggers for compliance pathways.

12. Do these changes influence how Melt Code interprets CBC 2025?

Yes. Definitions determine reasoning logic. Melt Code will use the updated definitions to interpret occupancies, envelope systems, fire protection triggers, IT room classifications, and temporary structure rules with higher accuracy and jurisdiction-specific clarity.

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References

1. ‍2022 California Building Code, Title 24, Part 2 (Volumes 1 & 2) with July 2024 Supplement updated

2. 2025 California Building Code Volumes 1 and 2, Title 24, Part 2