California Assembly Bill 2533:
A New Pathway to Legalizing Unpermitted ADUs

Typical California backyard ADU
(image: Pacific Legal Foundation)

Frequently described as an “amnesty” program, AB2533 is often misunderstood to mean that unpermitted ADUs are exempt from all building code requirements. While the legislation does provide broad relief from many code provisions, it is not a blanket amnesty. Instead, it relies primarily on select provisions of the California Health and Safety Code as the governing standard. Building elements that may not comply with current building codes, but that do satisfy minimum health and safety requirements, may be allowed to remain, while elements that fail to meet either standard must be corrected to achieve compliance.

This article examines how AB2533 works, the extent of the relief it provides, and what is required when that relief does not apply.

Background
Prior to the passage of AB2533 and its predecessor, SB 897, ADUs constructed without permits were generally required to conform to all model code requirements in effect at the time legalization was sought. By “model code” is meant the entirety of California’s adopted code spectrum, including the Building, Residential, Electrical, Mechanical, Plumbing, Energy, Fire, and Green Building (CALGreen) codes, as well as the California Energy Efficiency Standards. This meant that all aspects of an unpermitted ADU could be scrutinized for conformance to current code.

Using the California Electrical Code as an example, prior to AB2533 enforcement could extend to items such as clearance in front of electrical panels, feeder type and sizing, and outlet and switch locations. Enforcement of the California Energy Efficiency Standards could require installation of thermal insulation in walls or ceilings, or even wholesale replacement of water or space-heating systems if they failed to meet current performance requirements.

Under AB2533, only those conditions that do not comply with applicable health and safety standards—specifically those enumerated in California Health and Safety Code Section 17920.3—are required to be corrected. In the electrical example cited above, the operative requirement becomes simply that the building’s wiring be in good and safe working condition. In the case of the energy code, because energy efficiency is not itself a health or safety consideration, conformance with the California Energy Efficiency Standards becomes limited, generally applying only where the unit’s heat source is deficient or entirely lacking. In such cases, any newly installed heat source must meet current energy efficiency standards.

California Health and Safety Code Section 17920.3
Section 17920.3, which AB2533 establishes as a minimum standard, enumerates those conditions that, if present, constitute a danger to the life, health, safety, or welfare of a building’s occupants, to the property itself, or to neighboring persons or property. Buildings failing to meet these standards are deemed “substandard” and therefore require correction.

The statute organizes these conditions into fifteen major categories addressing sanitation, structural integrity, nuisances, electrical, plumbing, and mechanical systems, weather protection, fire hazards, materials of construction, site conditions, means of egress, fire-resistive construction, occupancy and use, and resistance to lateral forces. Within these categories, the law identifies specific deficiencies such as inadequate sanitation and utilities, structural deterioration or undersizing, infestation, mold, improper maintenance, unsafe wiring or plumbing, insufficient exits or fire protection, and hazardous accumulations on the premises.

Importantly, Section 17920.3 emphasizes present safety and habitability rather than strict conformity to modern building codes. Certain existing conditions may be allowed to remain if they were lawful when installed and are currently safe and properly maintained. In this way, the statute frames substandard status around actual risk, not technical nonconformance.

How AB2533 Gets Implemented
Under AB2533, local agencies are required to develop a checklist based on Section 17920.3, which serves as the jurisdiction’s standard for evaluating pre-2020 ADUs seeking legalization. A local agency may not deny a permit for such a unit unless, when measured against this checklist, the ADU is found to be substandard.

Only those portions of the unit identified as substandard may then be required to be brought into compliance with current code requirements, and only to the extent necessary to cure the substandard condition. This targeted procedure—examining only those portions that fail to meet minimum health and safety standards rather than conducting a wholesale forensic review of the entire structure—makes legalization more predictable, more straightforward, and significantly more affordable for ADU owners seeking relief under AB2533.

The Limits of AB2533 Relief
While AB2533 provides meaningful relief from many modern building code requirements, it is important to understand what the law does not do. The statute establishes a minimum health and safety threshold for legalizing certain pre-2020 ADUs; it does not override all other regulatory frameworks, nor does it eliminate the authority of local agencies to enforce standards outside that narrow scope.

First, AB2533 does not supersede zoning or land-use regulations unrelated to building safety. Issues such as floodplain requirements, coastal permitting, hillside or hazard overlays, or limitations on the number of dwelling units permitted on a parcel remain governed by local zoning ordinances and state planning law. An ADU that satisfies the health and safety criteria of Section 17920.3 may still be subject to limitation if it violates applicable land-use regulations or is located in a regulated hazard area.

Second, the statute applies only to ADUs and Junior ADUs constructed before January 1, 2020. Units built after that date are not eligible for the streamlined treatment provided by AB2533 and must comply with the full spectrum of applicable building and energy codes in effect at the time of legalization. Similarly, work performed after legalization—such as additions, structural alterations, or system upgrades—will generally trigger compliance with current codes for the scope of that work.

Third, AB2533 does not protect conditions that present an actual and ongoing safety risk. Elements that are structurally unsound, pose a fire hazard, lack adequate means of egress, or otherwise fall within the definition of “substandard” under Section 17920.3 cannot remain simply because they predate modern codes. Where a condition is deemed substandard, the local agency is authorized to require correction to current code standards to the extent necessary to eliminate the hazard.

Fourth, the law does not eliminate inspections or discretionary judgment by local building officials. While AB2533 limits the basis on which a permit may be denied, it does not remove the agency’s role in evaluating existing conditions against the health and safety checklist, interpreting observed deficiencies, or determining appropriate corrective measures. As a result, outcomes may still vary by jurisdiction and by the specific facts of a given unit.

Finally, AB2533 applies only to the process of legalizing an existing, unpermitted ADU. It does not freeze the unit in time or exempt it from future regulation. Once legalized, the ADU is treated like any other permitted dwelling, and future work on the unit must comply with the codes and regulations in effect at the time that work is proposed.

Understanding these limits is essential. AB2533 is best viewed not as a blanket amnesty, but as a calibrated policy tool—one that lowers the barrier to legalization while preserving the regulatory authority necessary to protect health, safety, and the public welfare.

A Practice-Based Legalization Strategy Under AB2533
While AB2533 establishes a statutory framework for legalizing certain unpermitted ADUs, the statute alone does not dictate how the process unfolds in practice. Experience shows that outcomes are shaped as much by early coordination, documentation strategy, and scope discipline as by the law itself.

Early Agency Consultation and Eligibility Confirmation
A prudent starting point is early consultation with key local agency staff, particularly representatives from both the planning and building departments. Planning staff with enforcement experience are often especially valuable, as they are familiar not only with AB2533 as policy, but with the practical mechanics of remedying unpermitted construction. A subsequent meeting—preferably with the Building Official—is equally important, as that office ultimately controls the application of health and safety standards on the building code side.

Before health and safety standards come into play, the owner must be able to demonstrate that the unit functioned as an ADU prior to January 1, 2020. This generally means establishing the presence of core dwelling features such as a bathroom, kitchen facilities, and a heat source during the relevant time period. Assessor’s records are a useful starting point but are often insufficient on their own. Supplemental documentation—such as lease agreements, real estate transaction records, home inspection reports, utility records, or dated photographs—may be necessary to substantiate eligibility.

Documentation of Existing Conditions and Checklist-Based Review
Once eligibility is reasonably supported, the next step is thorough documentation of existing conditions. This typically includes field measurements, preparation of as-built drawings, and systematic observation of the unit against the local jurisdiction’s AB2533 health and safety checklist. Each checklist item is evaluated explicitly: compliant conditions are documented, while noncompliant conditions are flagged for correction.

This review is intentionally bounded. The objective is not to perform a comprehensive forensic code analysis, but to identify only those conditions that fail to meet minimum health and safety standards and therefore require remediation under AB2533.

Discipline-Specific Roles and Use of Outside Consultants
In practice, the scope of professional evaluation is divided by discipline. Architectural review typically encompasses items such as means of egress, weather protection, general habitability, and observable structural conditions. Mechanical, electrical, and plumbing systems are treated differently. AB2533 checklists commonly require these systems to be inspected and certified by appropriately licensed contractors, and their evaluation falls outside the architect’s direct purview. The legalization strategy therefore anticipates reliance on reports and sign-offs from owner-retained specialty contractors, with the architectural drawings referencing and incorporating those findings as needed.

Where observed conditions suggest deficiencies beyond the architect’s expertise—such as evidence of structural distress, excessive deflection, or foundation movement—the issue is identified and the owner advised to retain the appropriate consultant, such as a structural engineer. That consultant’s recommendations are then integrated into the overall correction strategy.

Development of Targeted Working Drawings
Once all identified deficiencies are understood, corrections are selectively incorporated into a set of Working Drawings. These drawings are intentionally narrow in scope, addressing only those items necessary to cure substandard conditions identified through the checklist process. By resisting unnecessary upgrades or voluntary improvements, the risk of triggering additional code requirements outside AB2533’s intended relief is reduced.

Before submittal, the Working Drawings are reviewed with the owner in a progress meeting to ensure that required corrections, consultant inputs, and anticipated costs are clearly understood. Following client approval, the drawings are finalized and submitted for building department review.

Permit Review and Approval
Advance coordination with the Building Official regarding jurisdiction-specific interpretations or commonly flaged issues can materially improve the predictability of plan review. When eligibility has been well documeednted, the checklist properly applied, and the scope carefully controlled, the permit review process under AB2533 can proceed efficiently and without unexpected expansion.

Conclusion
AB2533 represents a meaningful shift in how California addresses long-standing, unpermitted ADUs—substituting proportional health and safety review for comprehensive retroactive code compliance. When applied as intended, the statute offers a rational path to legalization that improves habitability while acknowledging the realities of existing construction.

Realizing those benefits, however, depends on informed implementation. Careful eligibility documentation, disciplined scope control, early agency coordination, and appropriate use of professional expertise allow AB2533’s relief provisions to function as designed, converting informal housing into safe, legal dwelling units without the unnecessary hurdles that characterized the pre-AB2533 landscape.

For Further Reading
• The AB 2533 legislation can be found at:
https://leginfo.legislature.ca.gov/faces/billNavClient.xhtml?bill_id=202320240AB2533
• Section 17920.3 of the Health and Safety Code, referenced as the minumum standard for compliance, can be found at: https://law.justia.com/codes/california/code-hsc/division-13/part-1-5/chapter-2/section-17920-3/

See also
ADUs in Santa Cruz County: What are the Current Regulations?
Reflections and Insights: Implementing the Principles of the Not So Big House

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