Key Updates to the 2026 California Building Standards for ADU Projects

Technical guide for California architects preparing ADU submissions under the 2025 Title 24 update (effective January 1, 2026). Structured with numbered references to match other ADU Pilot briefings and ready for publication.

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TL;DR

• Title 24 (2025 edition) governs every permit filed on/after Jan 1, 2026, and residential standards will not be revised again until 2031 because of AB 130—plan standard details and city pre-approved sets accordingly.[1][2]
• CBC 2025 consolidates WUI rules, upgrades structural loads via ASCE 7-22, and demands more electrical/equipment clearances, so ADU design teams must document exterior assemblies, lateral calcs, and panel space upfront.[1][2][3]
• Energy Code 2025 pushes all-electric readiness—heat pumps, MERV 13 ventilation, heat-pump water heaters, electric-ready kitchens, and ADU-specific solar PV/BESS-ready infrastructure become the default path to compliance.[5][6][7]
• CALGreen 2025 tightens resource and wellness measures with 1.2 gpm fixtures, 65% construction waste diversion, EV-capable raceways, bicycle parking, and low-VOC material requirements that must show up in specs.[8][9][10]
• Permitting strategy now hinges on refreshed standard plans, multidisciplinary coordination, and earlier feasibility checks to budget for electrification, solar, and longer plan-review queues.

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CBC 2025: Fire, Structural, and Electrical Implications

The California Building Code update effective January 1, 2026 reshapes core technical criteria for ADU design packages.

Wildland-Urban Interface (WUI) consolidation

CBC 2025 introduces a standalone California Wildland-Urban Interface Code (Title 24, Part 7) absorbing the old Chapter 7A/CRC R337 language.[1] For ADUs in Very High Fire Hazard Severity Zones, submittals must show Class A roofing, ember-resistant venting, non-combustible siding, and fire-rated glazing per Part 7 tables. Include ICC ESRs, WUI approvals, and detail sheets in the initial package; incomplete exterior schedules will trigger corrections under the unified reference.

Structural design under ASCE 7-22

The cycle adopts ASCE 7-22, updating wind speeds, seismic coefficients, and drift checks for light-frame wood structures.[2] Even 400–800 sq ft ADUs now require recalculated lateral systems, hold-downs, and diaphragm chords. Coordinate with structural engineers early so architectural (A-series) sheets, structural (S-series) sheets, and Title 24 calcs agree on site class, load combinations, and connection nailing schedules.

Electrical + equipment space planning

Electrification momentum shows up in both CBC and CRC with higher expectations for working clearances and future load capacity.[3] Detached ADUs often need upsized primary services (200A), dedicated 70–100A feeders, and closets or utility walls that respect NEC workspace dimensions. Clearly block out panel locations, EV circuits, and dual 240V appliance feeds on the electrical (E-series) sheets.

ADU-specific fire sprinkler relief

The statutory carve-out remains: if the primary dwelling did not require sprinklers, a new detached ADU cannot be forced to install them.[4] Cite this in the code data block to avoid unnecessary sprinkler comments. ADUs reviewed under CRC can continue to follow the single-family process while documenting R-3 occupancy details.

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2025 Energy Code: HVAC, Ventilation, Heat Pumps, Electrification

Title 24 Part 6 makes all-electric ADUs the path of least resistance for compliance modeling.

Heat pumps everywhere

Heat pump space conditioning is the prescriptive baseline for low-rise residential construction.[5] Specify ducted or ductless systems sized for ADU loads, call out condensate routing, and highlight exterior unit setbacks to keep plan reviewers aligned with acoustics and maintenance clearance.

Mechanical ventilation + filtration

Updated ASHRAE 62.2-2022 ventilation rates and MERV 13 filtration apply to central systems.[6] Even compact ADUs require continuous mechanical ventilation (HRV/ERV or balanced exhaust) with labeled airflow rates and duct materials. Show supply/exhaust terminations and controls on mechanical sheets to avoid rechecks.

Hot water + electric-ready circuits

Heat pump water heaters (HPWHs) align with the new prescriptive efficiency tables.[5] Pair them with dedicated 240V circuits and condensate drains, then note the locations on plumbing and electrical drawings. Kitchens must now be electric-ready—reserve a 240V/50A circuit and junction box near the cooktop, plus spare circuits for dryers and future HVAC electrification.[5]

Solar PV and BESS readiness

Detached ADUs must install their own compliant solar PV arrays; sharing a system with the primary home no longer satisfies Part 6.[7] Plan sets need array sizing, interconnection one-lines, and Battery Energy Storage System (BESS)-ready conduit plus wall space even if storage is deferred.

Building envelope refinements

Higher insulation R-values and improved fenestration U-factors now apply across climate zones. List wall/roof assemblies, window specs, and NFRC data directly in the envelope schedule so Title 24 documentation (CF1R/CBECC) matches the architectural sheets.

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CALGreen 2025: Water, Waste, EV, Bicycle, and Low-VOC Measures

Title 24 Part 11 extends sustainability requirements to even the smallest ADUs.

Water conservation fixtures

Lavatory flow maximums drop to 1.2 gpm and kitchen faucets must auto-reset to 1.8 gpm.[8] List manufacturer/model numbers that meet these limits in the plumbing fixture schedule and spec section.

Construction Waste Management and material health

All residential projects must submit a Construction Waste Management (CWM) Plan demonstrating at least 65% diversion via recycling or reuse.[9] Pair that with low-VOC material specifications (paints, coatings, adhesives, flooring) that reference CARB Phase 2 limits and include ventilation flush-out instructions on the finish schedule.

EV-capable and bicycle infrastructure

One- and two-family lots (including ADUs) remain EV Capable: install a raceway from the service panel to parking and reserve breaker capacity for a future 40A, 208/240V circuit.[10] Multifamily parcels escalate to Level 2 EV-ready outlets at each space, plus new bicycle parking requirements that may dictate long-term indoor storage or secure exterior lockers. Document conduit routing, panel space, and bike parking dimensions on site/electrical sheets so plan reviewers can verify compliance.

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Impact on Permitting, Feasibility, and Design Strategy

Refresh standard plan catalogs

City pre-approved ADU plans must be updated for the 2025/2026 code cycle. Verify any template’s Title 24, structural, and CALGreen references before submitting; outdated sets may fail plan check or require re-issuance.

Feasibility + cost modeling

Electrification, HPWHs, solar PV, and BESS-ready infrastructure raise upfront costs while lowering operational loads. Blend these capital expenses into feasibility memos alongside incentives/tax credits so owners understand ROI over the statute’s long cycle.

Integrated design workflow

Adopt checklists that align architecture, structural, MEP, and energy consultants on ASCE 7-22 loads, ventilation rates, HPWH specs, EV circuits, and waste plans before DD. Document everything in the permit set to shorten review loops.

Schedule awareness

Plan review queues may extend as jurisdictions retrain staff on the new standards. If you aim to submit under pre-2026 rules, confirm completeness early; otherwise, build the new requirements into timelines and client communications.

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Technical Case Study: 800 sq ft All-Electric ADU

• HVAC: Ductless mini-split heat pump sized for Manual J loads; outdoor unit on a vibration-isolated pad, indoor heads in living/bed zones.
• Ventilation: Heat Recovery Ventilator (HRV) located in a utility closet, ducted through the attic to supply living/bedrooms and exhaust bath/kitchen while meeting ASHRAE 62.2 airflow tables.[6]
• Hot water: 50-gallon HPWH inside a vented closet with condensate drain and dedicated 240V/30A circuit, exceeding the new UEF targets.[5]
• Envelope: 2x6 walls with R-21 cavity insulation, R-38 attic insulation, and low-e dual-pane windows meeting updated U-factor and SHGC tables for the project’s climate zone.
• Electrical + solar: New 200A service with a 3 kW south-facing PV array, BESS-ready conduit to a garage wall, and EV-capable raceway to the driveway, satisfying Part 6 and CALGreen requirements.[7][10]

This combination shows how thoughtful coordination can deliver a high-performance ADU that meets every 2026 requirement without triggering redesign late in plan check.

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Conclusion

The 2025/2026 Title 24 cycle is the foundation California architects will work under for years. By integrating WUI assemblies, ASCE 7-22 structural criteria, electrification-ready systems, CALGreen resource measures, and updated permitting workflows now, ADU teams can stay ahead of reviewer expectations, deliver resilient housing, and guide clients through the most significant code shift of the decade.

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References

[1] California Department of General Services (DGS), Building Standards Commission. "2025 Part 2 Chapters 5, 7, 7A and 8." 2025 Title 24 California Code Changes. https://www.dgs.ca.gov/BSC/Resources/2025-Title-24-California-Code-Changes/2025-Part-2-Chapters-5--7--7A-and-8

[2] California Department of General Services (DGS), Building Standards Commission. "2025 Part 2 Chapters 16 and 16A Structural Design." 2025 Title 24 California Code Changes. https://www.dgs.ca.gov/BSC/Resources/2025-Title-24-California-Code-Changes/2025-Part-2-Chapters-16-and-16A-Structural-Design

[3] Express Electrical Services. "AFCI & GFCI Requirements in 2025 Homes." October 2, 2025. https://expresselectricalservices.com/understanding-new-safety-standards-afci-gfci-requirements-in-2025-homes/

[4] California Department of Housing and Community Development (HCD). "Accessory Dwelling Unit Handbook." January 2025. https://www.hcd.ca.gov/building-standards/adu/handbook

[5] California Energy Commission. "2025 California Energy Code Fact Sheet." https://www.energy.ca.gov/sites/default/files/2024-09/2025_California_Energy_Code_Fact_Sheet_ada.pdf

[6] California Energy Commission. "2025 Energy Code Overview." https://www.energy.ca.gov/sites/default/files/2025-06/2025_Energy_Code_Overview_ADA.pdf

[7] California Energy Commission. "2025 Energy Code Accessory Dwelling Units (ADU) FAQs." https://www.energy.ca.gov/programs-and-topics/programs/building-energy-efficiency-standards/energy-code-support-center-6/2025

[8] International Code Council (ICC). "2025 California Green Building Standards Code, Title 24, Part 11." https://codes.iccsafe.org/s/CAGBC2025P1/appendix-a5-nonresidential-voluntary-measures/CAGBC2025P1-AppxA5-SecA5.303

[9] CalRecycle. "2019, 2022 & 2025 CALGreen Construction Waste Management Requirements." https://www2.calrecycle.ca.gov/Docs/Web/116820

[10] CalGreen Energy Services. "EV Charging and the 2025 CalGreen Code." November 18, 2025. https://calgreenenergyservices.com/2025/11/18/ev-charging-and-the-2025-calgreen-code/