What are the key changes in Chapter 5 General Building Heights & Areas of CBC 2025?

Chapter 5 contains some of the most consequential changes for architects and code consultants, particularly around:

1. California’s Restriction on the Allowable Area Equation (Sa)

• CA removes the Sa = 4 multiplier entirely.
• Sa is capped at:
  
  • Sa = 2 for Groups A, E, H, I, L, R
  • Sa = 3 for all others
    This dramatically affects allowable areas for many project types.

2. Group I-2 height limitations tightened

• Group I-2 is no longer permitted in Types IIIB and VB at any height.

3. Occupiable roofs  -  reorganized with new exceptions

Especially the new exception for roofs ≥75 feet above fire department access.

4. Mixed-occupancy area calculation rule (Equation 5-3) lowered

• Applied to buildings >2 stories instead of >3 stories.

5. Frontage increase rules clarified

New limitations on what qualifies as a 30’ open space for frontage.

6. Live/Work units receive updated sprinkler and alarm requirements

These changes influence early feasibility studies and schematic design layouts more than almost any other chapter.

Full Detailed Table Of All Changes  -  Chapter 5

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Expert Commentary  -  Chapter 5

1. The Sa restrictions are one of the biggest California-specific shifts in years

This reduces allowable building areas significantly  -  especially for:

• Schools (E)
• Assembly (A)
• Hospitals (I-2)
• Apartment buildings (R)

Design teams operating from IBC assumptions must re-run allowable area studies.

2. Group I-2 height restriction

This is a critical update for healthcare projects and essentially eliminates Type V hospital expansions.

3. Mixed-occupancy Equation 5-3 change

Many mixed-use multifamily podium buildings 3 stories or fewer were previously exempt  -  not anymore.

4. Mass timber (IV-B / IV-C) keeps gaining usability

The removal of thermal barrier requirements reduces costs and thicknesses, and keeps California aligned with national tall mass timber trends.

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FAQs

1. What is the most impactful change in Chapter 5 for architects and engineers?

The biggest shift is California’s new cap on the allowable area coefficient (Sa):

• Sa = 2 max for Groups A, E, H, I, L, R
  
• Sa = 3 for all other groups

California also removed the Sa = 4 multiplier entirely. This dramatically reduces allowable building areas and requires teams to redo all early massing studies, especially schools, apartments, and hospitals.

2. How do the new Sa limits affect feasibility studies?

Area calculations that previously worked under IBC or 2022 CBC assumptions may no longer comply. This directly impacts:

• Site test fits
  
• Podium/massing diagrams
  
• FAR studies
  
• Early design packages
  

In many project types, especially E, A, I-2, and R, allowable area may shrink by 30–50% depending on configuration.

3. What changed for Group I-2 (Hospitals/Medical Facilities)?

A major restriction: Group I-2 is no longer allowed in Types IIIB and VB, at any height.
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This means:

• No more Type V hospital wings or expansions
  
• No Type IIIB medical towers
  
• More projects will be forced into Type IIA, IIB, or Type I construction
  

This aligns California with stricter healthcare safety performance expectations.

4. What’s new for occupiable roofs?

Section 503.1.4 was reorganized and now includes a key new exception:
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‍Rooftop enclosures (stairs, elevators, etc.) are allowed above occupiable roofs if the roof deck is 75 ft or more above fire department access.

Translation: tall buildings get more freedom for rooftop amenities—pools, lounges, terraces—without violating height limitations.

5. How does the new mixed-occupancy Equation 5-3 rule change affect mixed-use buildings?

The threshold for applying Equation 5-3 dropped from >3 stories to >2 stories.
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This means:

• Many 3-story mixed-use podium or multifamily-over-retail buildings must now use reduced allowable areas.
  
• Standard assumptions for 3-over-1 and 4-over-1 models may no longer pass without design adjustments.
  
  

6. What changed in frontage increase calculations?

Section 506.3.3.1 tightens what qualifies as usable open frontage:

• Only the smallest public way/open space counts
  
• Open space must be ≥30 ft in width
  
• Table column revised to “55 or greater”
  

This reduces allowable area for sites relying heavily on frontage.

7. What updates affect live/work units?

Live/work requirements were reorganized for clarity, and fire protection rules updated:

• Must use NFPA 13 or 13R sprinklers
  
• Smoke alarms per 907.2.11
  
• Manual fire alarm required per 907.2.9.2
  
• CRC buildings follow CRC fire protection rules
  

This clarifies a previously confusing mix of commercial/residential triggers.

8. How did mass timber buildings benefit in this cycle?

For Type IV-B and IV-C, the CBC removes the need for a thermal barrier on top of horizontal assemblies when used for incidental use separations.
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This:

• Lowers costs
  
• Reduces assembly thickness
  
• Keeps CA aligned with national tall wood code adoption trends
  
  

9. What separation rule was removed for mixed institutional buildings?

Section 508.2.4 Exception 4—which previously allowed certain B/E/R-1 and S-2 spaces accessory to I-3 without separation—was deleted.
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Now, more separation is required between institutional occupancies and accessory uses.

10. Do these changes make buildings safer or just more restrictive?

Both.

• Sa limits and I-2 height restrictions strengthen life safety.
  
• Occupiable roof rules and mass timber allowances increase design flexibility.
  
• Frontage and mixed-occupancy rules clarify long-standing ambiguities.
  

Overall, Chapter 5 is more precise, more restrictive in key risk categories, and more permissive in areas tied to modern building types (rooftops, mass timber).

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