What are the major changes in the 2025 California Building Code Volume 1?
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The 2025 California Building Code Volume 1 introduces sweeping updates across administration, occupancy classifications, fire protection systems, accessibility, building envelopes, energy storage/lithium-ion battery safety, construction types, and means of egress.
Across all chapters, the most significant thematic changes include:
1. Complete relocation of Wildland–Urban Interface provisions
- CBC Chapter 7A is fully deleted
- All WUI requirements moved to the new California Wildland-Urban Interface Code (Part 7)
2. Major statewide updates for lithium-ion battery hazards
- New classifications for occupancies involving Li-ion storage, manufacturing, R&D, and vehicle charging
- New sprinkler triggers in Groups B, F-1, S-1, M
- New fire alarm/detection requirements
- New test-based sprinkler design for Li-ion hazards
3. Adjustments to allowable building areas & heights
- California deletes the Sa = 4 multiplier from Equation 5-2; CA restricts Sa to 2 or 3 depending on occupancy
- Group I-2 height limitations tightened
4. New & revised definitions affecting fire protection, construction, IT spaces, and materials
Including:
- Occupiable roof
- Data center vs. computer room
- Continuity head-of-wall system
- Insulated vinyl siding
- Metal building systems
5. High-rise and special occupancy changes
- New rules for stairway re-entry
- Revisions for care suites in I-2
- New atrium exceptions for Group I-2/R-2.1
6. Updated fire-resistance continuity and support requirements
- Multiple clarifications around columns, beams, floor/roof continuity, and exterior wall rating continuity
7. Sprinkler system and fire alarm system updates
- Large additions for lithium-ion systems
- Integrated systems testing section deleted
- New signage rules for FDCs
- Revised NFPA 13R applicability limits
8. Means of egress clarifications
- Door hardware (new definitions), bolt restrictions, new exceptions
- Stairway door locking revisions
- Expanded emergency illumination rules
- New guard exceptions for occupiable roofs
9. Accessibility (Chapter 11B) refinements
- Updates for transient lodging vs. educational housing
- EVCS clarifications
- Detailed revisions for dwelling units with adaptable features
10. Envelope, cladding, WRB, vapor retarder, IMP, and EIFS regulations expanded heavily
- Exterior wall assembly fire propagation rules tightened
- Multiple new sections for vinyl siding, polypropylene siding, IMP, BIPV, and flashing
11. Roofing updates
- Wind speed thresholds changed
- Deck ventilation and spacing clarified
- New lightning protection & raised deck systems sections
What are the key changes in Chapter 1 Administration of CBC 2025?
High-Impact Summary
Chapter 1 introduces strengthened powers for building officials, clearer record-keeping mandates, formalization of peer review authority, clarification of permit exemptions, and expanded definitions for temporary structures and equipment. These changes collectively give AHJs more explicit authority and create clearer compliance expectations for applicants.
Key impacts:
- Building officials now have greater authority to determine compliance and request peer reviews.
- Swimming pool barriers are no longer exempt from permits.
Temporary permits now include equipment/systems and are capped at one year max.
Full Detailed Table of All Changes - Chapter 1
What are the key changes in Chapter 2 Definitions of CBC 2025?
High-Impact Summary
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.
What are the key changes in Chapter 3 Occupancy Classification & Use of CBC 2025?
High-Impact Summary
Chapter 3 introduces major reclassifications in response to new risks associated with lithium-ion batteries, changes to childcare occupancy limits, residential occupancy definitions, and expansions to storage and factory occupancies. These updates affect how buildings are classified, which in turn triggers fire protection requirements, allowable areas, egress rules, and separation requirements.
Top high-impact changes:
- Lithium-ion battery activities are now explicitly classified under Groups B, F, and S.
- Beverage alcohol thresholds raised from 16% to 20% for F, S, and storage groups.
- Group E childcare rules expanded for infants/toddlers.
- New clarity for R-1 and R-2 occupancies (transient dwellings and emergency service quarters).
- Group H rooftop storage replaces the previous “outdoor storage” terminology.
- Big update to MAQs for hazardous materials across Table 307.1(1) & (2).
What are the key changes in Chapter 4 Special Detailed Requirements Based On Occupancy & Use of CBC 2025?
High-Impact Summary
Chapter 4 sees substantial changes, especially for high-rise buildings, atriums, care suites in I-2 occupancies, hazardous materials, and special amusement areas.
The most significant changes include:
- New glass wall rules for high-rise buildings
- Revised stairway re-entry door operation requirements
- Expanded atrium enclosure exceptions (especially for I-2/R-2.1)
- New vehicle sallyport requirements for I-3
- Relocation of special amusement area alarm requirements
- Significant rewrites for care suite egress and access rules
- Updates throughout hazardous material sections
What are the key changes in Chapter 5 General Building Heights & Areas of CBC 2025?
High-Impact Summary
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.
What are the key changes in Chapter 6 Types Of Construction of CBC 2025?
High-Impact Summary
Chapter 6 focuses heavily on mass timber, thermal barriers, combustible materials, and fire resistance clarifications. Key themes:
1. More flexibility for Type IV-B (mass timber)
- 100% unprotected ceilings allowed in dwelling units or fire areas (up from 20%).
- Unprotected undersides of floors allowed via exceptions.
2. Clarification around concealed spaces
- Type IV-HT now requires protection only for combustible surfaces, not all surfaces.
3. Combustible materials allowed in Types I & II
- Combustible vapor retarders are now permitted.
- Combustible plumbing fixtures allowed.
4. Structural fire resistance continuity clarified
Important for mezzanines, exterior structural members, and horizontal separations.
Full Detailed Table Of All Changes - Chapter 6
Expert Commentary - Chapter 6
1. Mass Timber Continues Its California Expansion
Type IV-B & IV-C design is becoming significantly easier and more aesthetic-friendly.
This aligns with:
- sustainability goals
- carbon neutrality targets
- the push for mid-rise and tall wood structures
2. Clarification for Type IV-HT
Designers often struggled with interpreting required protections for concealed spaces. This change prevents unnecessary application of fireproofing.
3. Combustible vapor retarders allowed in Types I & II
This is a major shift for building envelope designers - it enables advanced vapor-smart WRBs and high-performance walls commonly used in other states.
What are the key changes in Chapter 7 Fire & Smoke Protection Features of CBC 2025
Chapter 7 of the 2025 California Building Code introduces major clarifications to fire-resistance continuity, expanded protection requirements for structural members, new rules for mass timber assemblies, and updated provisions for penetrations, openings, joints, and shaft enclosures.
Key themes include:
- More explicit requirements for continuous fire-resistance rating protection, especially for structural columns, exterior walls, and primary/secondary structural frame members.
- Updated rules for horizontal and vertical continuity of fire-resistance-rated assemblies, including new exceptions for Groups I-2 and high-rise buildings.
- New allowances and clarifications related to mass timber (Type IV), exterior curtain wall intersections, and parapet construction.
- Revised regulations around penetrations, through-penetration firestop systems, sleeves, and mechanical/electrical penetration controls.
- Multiple new or revised exceptions improving pathways for shafts, smoke partitions, opening protection, and fire barriers, particularly in hospitals and institutional occupancies.
This chapter significantly impacts architects and engineers working on healthcare, high-rise, mass timber, and mixed-use projects, with numerous detailed revisions that affect fire modeling, separation strategies, and rated assembly detailing.
What are the key changes in Chapter 8 Interior Finishes of CBC 2025?
The 2025 CBC updates interior finish classifications, clarifies smoke-developed index requirements, and introduces new rules for foam-plastic interior trim. Changes mainly impact hospitals (I-2), special psychiatric units, and any occupancy with combustible decorative elements.
High-Impact Summary
Chapter 8's updates revolve around clarifying finish classifications, updating occupancy-specific requirements, and adding new provisions for foam-plastic interior trim, which ties into both flame-spread and smoke development performance.
High-impact themes:
- Updated smoke-developed index requirements for all interior finishes
- Significant change to Group I-2 finish requirements
- New regulation for foam plastic interior trim
Full Detailed Table of All Changes - Chapter 8
Expert Commentary - Chapter 8
- The I-2 change is not minor - psychiatric floors now require I-3 finish compliance, which are far stricter.
- Many materials used in healthcare environments may no longer qualify unless re-evaluated.
- The new foam-plastic section is important for designers incorporating decorative panels, carved foam trim, or factory-produced interior components.
What are the key changes in Chapter 9 Fire Protection Systems of CBC 2025?
Chapter 9 undergoes one of the largest updates in the entire 2025 CBC, driven by rapid growth in lithium-ion batteries, energy storage systems, and battery-powered vehicles. Nearly every fire suppression and alarm section has been updated - including sprinkler triggers, special hazard protection, fire alarms in labs, lithium battery storage, hybrid extinguishing systems, new FDC signage requirements, and NFPA 13R allowances.
This chapter has substantial impacts on architects, engineers, and fire officials designing any building with batteries, labs, parking garages, EV repair areas, or mixed-use residential.
What are the key changes in Chapter 10 Means of Egress of CBC 2025?
The 2025 CBC introduces extensive updates in Chapter 10, reshaping how designers approach door hardware, stairway re-entry, occupant load factors, emergency illumination, guard requirements, accessible egress, occupiable roofs, exit arrangement, and assembly seating. Changes include new limitations on bolts and latches, revised door-size exceptions, added allowances for refrigeration machinery rooms, updated handrail and guard exceptions, expanded emergency lighting rules, and new two-way communication system standards. Designers must reassess door hardware packages, stair core planning, exit strategy for new occupiable roofs, and travel distance limits for hazardous occupancies.
The chapter covers the following key elements:
- door hardware
- egress sizing
- exit separation
- emergency lighting
- occupiable roofs
- accessibility
- handrails, guards, stair geometry
- assembly seating
- refrigeration rooms
- elevator lobbies
- communication systems
For a detailed breakdown of changes in Chapter 10 of California Building Code Volume 1, read here
What are the key changes in Chapter 11A Housing Accessibility of CBC 2025?
The 2025 CBC narrows the scope of Chapter 11A by removing newly constructed covered multifamily dwellings that also qualify as public housing from 11A and pushing them entirely into Chapter 11B. In practice, this means some projects that previously had to juggle both 11A and 11B will now be governed solely by 11B, simplifying - but also tightening - accessibility compliance for public housing projects.
High-Impact Summary
Chapter 11A has one primary but important change: it removes certain public-housing-type projects from the 11A regime and routes them fully under 11B.
Specifically, newly constructed covered multifamily dwellings that can also be defined as public housing are no longer subject to 11A; they remain governed by Chapter 11B only.
This:
- Reduces overlapping/duplicative application of both 11A and 11B
- Clarifies that public housing is treated like public facilities rather than private housing
- Tightens expectations, since 11B is generally more stringent and more closely aligned with ADA/Title II/Title III enforcement
Full Table of Changes - Chapter 11A
What are the key changes in Chapter 11B Accessibility to Public Buildings & Public Housing of CBC 2025?
Chapter 11B receives a series of clarifications, scope refinements, and corrections that clean up how accessibility applies to transient lodging, housing at places of education, EV charging stalls, public housing units with mobility/adaptable features, blended transitions, bathroom clearances, and dining surfaces. The changes don’t radically rewrite accessibility, but they close gaps, fix conflicts, and sharpen scoping, especially for public housing, student housing, and transient lodging.
For a detailed breakdown of changes in Chapter 11B of California Building Code Volume 1, read here
What are the key changes in Chapter 12 Interior Environment of CBC 2025?
Chapter 12 expands its scope beyond traditional interior environment requirements to now include classroom acoustics, ultraviolet germicidal irradiation (UVGI) systems, moisture control updates, dwelling unit minimum areas, and sound transmission requirements that now must be prepared by a registered design professional. The chapter modernizes indoor environmental quality requirements, clarifies insulation provisions (especially condensation control), and adds detailed provisions for adult changing table surrounds.
High-Impact Summary
Chapter 12’s updates focus on interior environmental quality via:
- Updated condensation control & insulation provisions
- Sound transmission analysis requiring design professionals
- Dwelling unit minimum square footage adjustments
- New UV Germicidal Irradiation Systems section
- New adult changing table criteria
- Extensive OSHPD-related refinements for healthcare facilities
Most impactful for architects working in housing, education, healthcare, and high-performance building envelopes.
Full Detailed Table of Changes - Chapter 12
Expert Commentary - Chapter 12
This chapter bridges architectural design with building science. The updated condensation control table and sound transmission requirements address common failure points:
- Mold behind insulation
- Poor acoustic separation
- Conflicts between building envelope and mechanical loads
What are the key changes in Chapter 14 Exterior Walls of CBC 2025?
Chapter 14 undergoes one of the largest transformations in the 2025 CBC, including sweeping updates to weather barriers, vapor retarders, flame propagation performance for exterior wall assemblies, vinyl siding installation, polypropylene siding, insulated metal panels (IMP), building-integrated photovoltaics (BIPV), and fire performance of cladding systems. It reorganizes entire sections, adds numerous new subsections, and modernizes exterior envelope design to align with high-performance wall systems and post-Grenfell façade safety trends.
Chapter 14 receives one of the most sweeping updates in the 2025 CBC. Themes include:
1. Complete restructuring and modernization of exterior wall provisions
Including:
- Exterior wall assemblies
- Soffits & fascias
- Cladding systems
- Water-resistive barriers (WRBs)
- Moisture control
- Vapor retarders
- Flame propagation limits
- New material-specific installation rules
2. Major emphasis on fire performance due to global façade fire incidents
CA incorporates tougher:
- Vertical flame propagation standards
- NFPA 285 acceptance criteria
- Materials using combustible adhesives
- Exterior insulation requirements
3. New categories of advanced cladding
Such as:
- Insulated vinyl siding
- Polypropylene siding
- Fiber-mat cementitious backer units
- Insulated metal panels (IMP)
- Building-integrated photovoltaics (BIPV)
4. Holistic reorganization
The entire chapter is made more coherent and aligned with modern building enclosure practices.
For a detailed breakdown of changes in Chapter 14 of California Building Code Volume 1, read here
What are the key changes in Chapter 15 Roof Assemblies & Rooftop Structures of CBC 2025?
Chapter 15 introduces updated wind resistance requirements, revised underlayment tables with new wind speed thresholds, new requirements for slate shingles, ventilation requirements for wood shake/wood shingle roofs, provisions for lightning protection systems, and detailed criteria for raised-deck systems installed over roof assemblies. These updates modernize roofing provisions and align with evolving climate, moisture, and wind conditions.
High-Impact Summary
Chapter 15 updates roofing to reflect:
- Higher wind loads
- Updated underlayment fastening requirements
- Specific safety detailing for wood shingles/shakes
- Growing need for lightning protection
- New complexity around raised deck systems over roofs
Full Detailed Table of Changes - Chapter 15
Expert Commentary - Chapter 15
This chapter modernizes roofing for California’s current climate risks:
- Wind uplift from atmospheric river events
- Moisture management under wood shingles/shakes
- Growth of occupied roof decks
- Rising need for lightning protection in tall buildings
It aligns CBC with roofing realities seen in the field - especially the ventilation requirements under shingles and shakes, which correct longstanding moisture-related performance issues.
What this means for architects, general contractors, developers, owners, and engineers
These thematic changes will have distinct impacts across the building industry.
For Architectural Firms
The reclassification of building occupancy classifications (e.g., lithium-ion facilities in Section 306.2, foster care facilities in Section 308.3) and major changes to means of egress requirements will directly impact building programming, layout, and life safety design. New requirements for interior finishes (Section 806.6), enhanced classroom acoustics (Section 1207), and storm shelters (Section 423, referencing icc 500) will require new design considerations.
For General Contractors
New material and installation standards are a primary concern. The introduction of comprehensive requirements for shotcrete (Section 1908.1), intermodal shipping containers as a unique construction type (Section 3114), and mass notification systems (Section 917) creates new fields of compliance. Furthermore, the complete rewrite of construction site safety provisions (Chapter 33), mandating a detailed, pre-approved Site Safety Plan, fundamentally changes site management obligations.
For Developers & Owners
The financial and operational impacts are significant. Mandates for new or expanded fire sprinkler and alarm systems (Sections 903, 907), especially in relation to lithium-ion batteries, increase upfront costs. Changes to allowable building area calculations (Section 506.2.1) could affect a project's pro forma. The transfer of enforcement for some facilities from state to local agencies (Section 1.10.6) alters the entire permitting and inspection pipeline.
For Engineering Firms
Structural Engineers face a litany of changes. The deferral to ASCE 7-22 for seismic design category determination, wind, and now tornado loads (Sections 1609, 1613, 1615) requires careful application of various load combinations. The complete restructuring of prescriptive foundation wall design (Section 1807) and the removal of certain live load reduction methods (Section 1607.12) will change common calculation procedures for every bearing wall.
MEP Engineers
must contend with new requirements for mechanical ventilation (Section 1202.1), new electrical standards for healthcare occupancies (Section 407.11), and entirely new sections for UV germicidal systems (Section 1211) and mass notification systems (Section 917).
Navigating the new landscape: A call for proactive adaptation
The transition to the 2025 California Building Code is far more than a routine, triennial update; it represents a fundamental recalibration of building safety, administrative procedure, and design philosophy in the state. The changes are not isolated to a few niche disciplines. Rather, they form a cohesive, sweeping overhaul that redefines responsibilities, addresses modern hazards like lithium-ion batteries head-on, and realigns California codes with national standards in critical areas from structural loads to job site safety.
For every architect, engineer, contractor, and developer, passive awareness will not be enough. The sheer volume and impact of these revisions – from the new authority granted to Building Officials in Chapter 1 to the complete rewrite of foundation and site safety requirements – demand immediate and proactive engagement. The time to prepare is now. It is imperative for firms to:
Invest in training to bring all team members up to speed on the new provisions.
Audit and update internal standards, templates, and specifications to reflect the 2025 CBC.
Engage with local building departments to understand how they will interpret and enforce the significant administrative changes.
Thoroughly review referenced standards like ASCE 7-22, as compliance now hinges on mastery of these external documents.
Ultimately, navigating this new regulatory landscape successfully requires a commitment to diligent study and adaptation. The professionals who embrace these changes will not only ensure compliance but will also lead the way in constructing the safer, more resilient, and technologically advanced California of tomorrow.
FAQs
1. What are the biggest overall changes in the 2025 California Building Code?
The 2025 CBC introduces major updates affecting administration, occupancy classification, fire protection systems, hazardous materials, means of egress, accessibility, building envelopes, roofing, and structural design—plus major lithium-ion battery safety upgrades.
2. When does the 2025 CBC go into effect in California?
The 2025 CBC becomes mandatory statewide on January 1, 2026, unless a local jurisdiction adopts it earlier.
3. What happened to CBC Chapter 7A (Wildland–Urban Interface)?
Chapter 7A was deleted entirely. All WUI requirements now reside in the California Wildland-Urban Interface Code (Part 7).
4. How does the 2025 CBC address lithium-ion battery hazards?
Lithium-ion batteries now impact occupancy classification, sprinkler requirements, hazardous material thresholds, fire alarm design, and special hazard suppression. Specific triggers appear in Groups B, F-1, S-1, and M.
5. How do occupancy classifications change in CBC Chapter 3?
Key updates include:
- Li-ion battery activities placed in Groups B, F, S
- Alcohol thresholds raised from 16% → 20%
- Expanded infant/toddler rules for Group E
- Clearer R-1/R-2 definitions
- Rooftop hazardous storage reclassified under Group H
6. Did allowable building areas and heights change in 2025 CBC?
Yes. California eliminates the Sa = 4 multiplier and caps Sa at:
- 2 for Groups A, E, H, I, L, R
- 3 for all others
This significantly affects building size feasibility.
7. What are the major Chapter 1 administration changes?
Building officials gain expanded authority, permit exemptions clarified, digital submittals formalized, peer review authority added, and temporary structures are capped at 1 year.
8. How does CBC 2025 affect lithium-ion battery storage in buildings?
Battery storage triggers classification as S-1, additional sprinklers, enhanced detection, MAQ recalculation, and new protection rules in Chapter 9.
9. Did fire protection system requirements change?
Yes. Chapter 9 introduces:
- New Li-ion sprinkler/detection rules
- Updated NFPA 13R limitations
- New control logic for alarms in labs
- New FDC signage rules
- Revised fire pump and standpipe details
10. How does CBC 2025 impact means of egress design?
Door hardware definitions updated, locking/bolting limits revised, stair re-entry rules expanded, emergency illumination broadened, and new exceptions added for occupiable roofs and refrigeration rooms.
11. What changes were made to care facilities and Group I occupancies?
Updated care suite egress, revised I-2 height limits, new smoke compartment rules, and expanded allowances for atrium configurations in I-2 and R-2.1.
12. What are the major structural changes in the 2025 CBC?
California adopts ASCE 7-22 for wind, seismic, and tornado loads; revises foundation wall design, adjusts load reductions, updates mass timber allowances, and removes certain live-load reduction options.
13. How does CBC 2025 affect mass timber buildings (Type IV)?
More flexibility is added:
- IV-B: 100% exposed ceilings allowed
- Unprotected underside of floors permitted
- Clearer rules for concealed spaces
These changes reduce cost and simplify detailing.
14. What envelope and cladding changes appear in Chapter 14?
Massive updates include:
- New WRB/vapor retarder requirements
- Flame propagation rules
- New categories: IMP, insulated vinyl siding, PP siding, BIPV
- Tougher façade fire-performance criteria
15. What changed in roofing standards (Chapter 15)?
Higher wind design thresholds, updated underlayment fastening tables, new ventilation requirements for wood shingles/shakes, new lightning protection rules, and new raised-deck system requirements.
16. How does CBC 2025 redefine IT, server rooms, and data centers?
Chapter 2 now distinguishes data centers from computer rooms, affecting fire protection, cooling, electrical design, and occupancy classification for tech spaces.
17. What changed for accessibility in Chapters 11A & 11B?
- 11A: Removes newly constructed public-housing-type multifamily from 11A; they are governed solely by 11B.
- 11B: Updates for transient lodging, EV charging, student housing, adaptable dwelling units, bathroom clearances, and dining surfaces.
18. What new requirements affect interior environments (Chapter 12)?
New moisture control tables, sound transmission rules requiring licensed professionals, updated unit size rules, UVGI system requirements, adult changing table rules, and major healthcare refinements.
19. Does CBC 2025 change requirements for existing buildings?
Yes. Existing buildings face new rules across multiple chapters, but the most significant are in:
- Compliance with updated fire protection
- Revised structural provisions
- Updated reroofing and envelope requirements
- New guidance in the WUI code
20. How should architects, engineers, and developers prepare for CBC 2025?
Firms should:
- Train staff on lithium-ion, MAQs, and new Chapter 9 rules
- Update life-safety plans and egress templates
- Revise envelope & roofing details
- Recalculate allowable areas early
- Coordinate with AHJs on administrative changes
- Review ASCE 7-22 changes in depth
References
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