Who Owns Which Part of Title 24? The Agency Map Nobody Hands You

One cover, thirteen books

Open a Title 24 codebook and it looks like one code. It isn't. Title 24 is the California Building Standards Code — published in its entirety every three years by the California Building Standards Commission (BSC). The current 2025 Triennial Edition took effect statewide on January 1, 2026.

What sits under that one cover is a stack of separate books, organized into Parts numbered 1 through 12. Here's the wrinkle nobody points out: Part 2 splits into two books — the California Building Code (Part 2) and the California Residential Code (Part 2.5) — so the code itself describes the set as "thirteen parts." Twelve numbers, thirteen books.

The map:

• Part 1 — California Administrative Code
• Part 2 — California Building Code (CBC)
• Part 2.5 — California Residential Code (CRC)
• Part 3 — California Electrical Code
• Part 4 — California Mechanical Code
• Part 5 — California Plumbing Code
• Part 6 — California Energy Code
• Part 7 — California Wildland-Urban Interface (WUI) Code
• Part 8 — California Historical Building Code
• Part 9 — California Fire Code
• Part 10 — California Existing Building Code
• Part 11 — California Green Building Standards Code (CALGreen)
• Part 12 — California Referenced Standards Code

The Commission publishes. The agencies write.

Here's the thing: BSC doesn't write most of this. The legislature handed the pen to a rotating cast of state agencies, and BSC compiles and publishes what they adopt.

Verified against the Part 1 Preface (California Administrative Code, 2025 Edition): "The California legislature delegated authority to various state agencies, boards, commissions and departments to create building regulations to implement the State's statutes."

So a single page of the Building Code can carry rules written by the Department of Housing and Community Development (HCD), the Office of the State Fire Marshal (SFM), the Division of the State Architect (DSA), and the hospital-building authority — each in its own lane.

How to read the banner

Every adopted article carries a Matrix Adoption Table — the small grid at the top — and an agency banner in brackets. The banner tells you who owns that provision. An italicized section number flags a state amendment; an X in an agency's column means that agency adopted it.

Verified against the live Article 517 (Health Care Facilities) Matrix Adoption Table in the California Electrical Code: the banner columns read BSC, BSC-CG, SFM, HCD, DSA, OSHPD, DPH.

One name to watch: OSHPD. The January 2026 errata renamed it from "Office of Statewide Health Planning and Development" to "Office of Statewide Hospital Planning and Development" across several Parts. The agency that actually adopts hospital and skilled-nursing standards today is HCAI — the Department of Health Care Access and Information. The OSHPD banner code still appears in the code text; the department behind it is HCAI.

Where to send the question

• Energy → California Energy Code (Part 6), adopted by the California Energy Commission.
• Fire and wildfire → California Fire Code (Part 9) and WUI Code (Part 7), Office of the State Fire Marshal.
• Accessibility → Access Compliance provisions, Division of the State Architect.
• Housing and residential → HCD.
• Hospitals, skilled nursing, clinics → HCAI (the OSHPD banners).

Most books are shared, not owned — which is exactly why the banner exists.

What January's errata actually touched

The January 2026 errata (BSC Information Bulletin 26-01) hit ten books across nine Part numbers — Parts 2 (Volumes 1 and 2), 2.5, 3, 4, 5, 6, 9, 10, and 11 — 121 corrections in all, ranging from 3 in the Mechanical Code to 25 in the Fire Code. Parts 1, 8, and 12 got no erratum at all, and Part 7 received a separate Emergency Supplement — a different instrument, not an erratum.

One correction per book, the kind you'd actually trip on:

• CBC (Part 2): single-exit doors may use manual bolts if they open from the inside without a key or tool (§1010.2.4).
• CRC (Part 2.5): the ADU fire-sprinkler exception is now restated in the code (R309.2, Exception 2).
• Electrical (Part 3): Article 517 moved OSHPD 1, 4 and 5 adoption from 517.1(B) to 517.1(C).
• Mechanical (Part 4): Table 1102.3 corrected the RCL/LFL safety values for A2L refrigerant blends.
• Plumbing (Part 5): Table 422.1 relocated a BSC and DSA-SS amendment to footnote 9.
• Energy (Part 6): Table 100.0-A fixed the section pointer for solar PV and battery storage.
• Fire (Part 9): Table 5003.11.2 corrected a gaseous max-allowable-quantity from 39,000 to 390,000 cubic feet.
• Existing Building (Part 10): §1504.1.4.1 corrected a panel thickness from "15/16 inch" to "5/16 inch."
• CALGreen (Part 11): Worksheet WS-2 footnote 4 now reads 0.35 gpm, not 35 gpm.

When in doubt on any of these, confirm the adopting-agency banner and verify with your local jurisdiction — a city amendment can sit on top of any of them.

What CrossBeam does with it

CrossBeam reads every Part of Title 24 the way a plan checker has to — by who adopted each provision, not just what it says. It tracks the agency banners and the errata that move them, so an energy question lands on the energy answer and a hospital scope shows up flagged. The map stays current so you don't have to rebuild it every cycle.