Title 24, 2025 edition: parts, effective dates and what changed

Title 24 of the California Code of Regulations is the state's building standards code: thirteen active parts, republished on a three-year cycle. The 2025 edition — adopted by the Building Standards Commission and effective statewide on January 1, 2026 — is the edition in force today. This page is a curated snapshot as of July 2026; the books themselves live in the library, starting with the California Administrative Code (Part 1), which governs how all the others get adopted.

The rule that matters most is the trigger: the edition in force on the date of the permit application governs the project. A December 2025 application runs on the 2022 books; a January 2026 application runs on the 2025 books — including the brand-new Wildland-Urban Interface Code (Part 7.5), which didn't exist as a standalone part before this cycle.

Part 7 has been vacant for years (elevator standards live elsewhere in state law); the 2025 cycle backfills the numbering gap with Part 7.5. Every part below except Part 3 is in the library as a full 2025-edition text.

The Building Standards Commission adopted the 2025 edition through its triennial rulemaking, and it took effect statewide on January 1, 2026. From there, three timing rules drive underwriting and design budgets. First, the permit application date fixes the edition — not when drawings started, not when the permit issues. Second, cities and counties may amend the state code for local climatic, geological or topographical conditions, but only with express findings filed with the state — and local amendments must be re-adopted against each new edition, so a 2022-cycle amendment doesn't automatically survive into 2026. Third, the state publishes intervening-cycle supplements between triennial editions that amend the in-force books on set effective dates.

• Underwriting watch-outs:
• A December 2025 application is a 2022-edition job even if construction runs through 2027 — resist "upgrading" the basis of design mid-permit without pricing it.
• An un-refiled local amendment is vulnerable: if the city can't produce current findings and the filing, push back before absorbing the cost.
• Supplements can move requirements between schematic design and the permit set — calendar the state's mid-cycle effective dates.
• Phased projects that pull permits across an edition boundary can end up with buildings on different books — decide the split deliberately.

Three themes headline the 2025 edition, all continuations rather than reversals. Part 6 continues the electrification arc — the Energy Code keeps pushing heat-pump-forward baselines and all-electric-friendly compliance paths, so gas-design assumptions carried over from older cycles need re-checking. CALGreen (Part 11) updates EV-readiness requirements for parking, the line item that most often surprises multifamily budgets carried over from earlier cycles. And the WUI reach expands: the new Part 7.5 consolidates wildland-urban interface construction standards just as updated fire-hazard mapping pulls more parcels — including urban-edge infill — into WUI scope.

• Underwriting watch-outs:
• Re-run the WUI map check even for infill sites: expanded hazard-zone mapping is how a project acquires ignition-resistant construction costs nobody budgeted.
• Don't spec 2022-era mechanical and EV assumptions into a 2026 application — the deltas concentrate exactly where per-unit costs live.
• CALGreen has voluntary tiers that local ordinances can adopt as mandatory — the city's reach can exceed the state baseline.