What is the ADU amnesty law and how does it affect MEP plans?

The ADU "amnesty" law refers to California's legalization pathway for unpermitted ADUs. AB 2533 (effective in late 2025) makes it substantially easier to bring an existing, previously unpermitted accessory unit into legal status, and it has direct implications for how MEP plans are prepared for these projects.

What the amnesty law does

For unpermitted ADUs built before January 1, 2020, AB 2533 limits a city's ability to deny legalization. Cities cannot deny a permit based on building-standard violations alone — they must allow the unit to be legalized as long as it does not present an imminent health-and-safety hazard. In other words, the goal is to fix and document non-compliant systems, not to force demolition of otherwise sound units. This brings many "shadow" units out of the unpermitted gray market and into a path where they are inspected, corrected, and recognized.

Why MEP is central to legalization

Unpermitted ADUs were, by definition, never inspected — so the active systems are where the violations concentrate. Plumbing tends to be the worst offender: in assessments of unpermitted units, a large majority showed plumbing deficiencies. Common problems include:

• Improper or missing drain venting (DWV not built to code).
• Undersized water supply lines.
• Missing backflow prevention.
• Improperly installed or unvented water heaters.
• Fixture connections that don't meet the California Plumbing Code.

Electrical violations are similarly common — non-GFCI outlets in wet locations, missing AFCI protection, panels without proper working clearance, double-tapped breakers, and reversed polarity. Mechanical issues center on non-residential or absent ventilation and heaters not rated for habitable space.

How amnesty MEP plans differ from a new build

The deliverable and process are similar to a standard ADU permit, but the starting point is reversed. Instead of designing systems from a blank slate, the MEP engineer must:

1. Document existing conditions — what is actually installed in the unit today.
2. Identify deficiencies — where the existing systems fall short of current code.
3. Design the corrective upgrades — the work needed to bring the unit to a compliant, safe standard.

The resulting plan set shows both existing and proposed conditions, so the plan checker and inspector can see what is changing and verify the unit reaches code. See our plumbing and electrical pages for what code-compliant systems must include.

Legalization is not a paperwork exercise — it is an engineering retrofit. The plans must prove the existing systems were brought up to code, which usually means a field assessment before drawings begin.

Practical guidance

• Have the existing systems assessed before assuming a unit is "close" to compliant — plumbing venting and electrical safety items are frequently hidden.
• Expect corrective construction, not just drawings.
• Confirm the unit's construction date and your city's amnesty intake process, since eligibility hinges on it.

Amnesty rules are new and vary by jurisdiction — confirm current eligibility and procedures with your local building department. If you are legalizing a unit, our team prepares MEP plans documenting existing conditions and required upgrades; start with the Full MEP Package or read the complete ADU MEP guide.