California Amnesty AB 2533 Explained: How to Legalize an Unpermitted ADU Without Paying Impact Fees

If you own a California property with a converted garage, a barn with an upstairs apartment, a "guest suite" above the pool house, or any other habitable space that was built or converted without permits — and it was in place before January 1, 2020 — you have a legalization pathway most homeowners have never heard of.

It's called AB 2533, codified at California Government Code §66332.5. It's part of a broader statewide push to unlock California's housing supply by bringing the state's estimated hundreds of thousands of unpermitted accessory dwelling units (ADUs) into the legal, taxable, insurable, and financeable housing stock.

For homeowners, the practical upside is significant: impact fees are waived, local standards that would normally disqualify the unit (size, setback, height, parking) cannot be enforced against amnesty applications, and the only enforceable standard is basic health and safety.

For anyone who's ever gotten a scary quote from a general contractor about "bringing it up to code," AB 2533 changes the math. Here's how it actually works.

The Short Version

• What it does: Requires every California city and county to accept legalization applications for ADUs built before January 1, 2020, without permits.

• What gets waived: Impact fees (school, park, traffic, affordable housing), local ADU development standards (size, setback, height, parking), and building-code compliance at time of construction.

• What still applies: Basic health and safety per Health & Safety Code §17920.3, standard building permit fees, plan check fees, and inspection fees.

• Who benefits: Any property owner with an unpermitted ADU, junior ADU, converted garage, or converted accessory structure predating 1/1/2020.

• Deadline: AB 2533's amnesty pathway is currently open. Legal exposure and enforcement risk grow the longer an unpermitted unit stays undocumented.

AB 671 vs. AB 2533 — Two Amnesty Laws, One Goal

The California ADU amnesty framework didn't arrive in one law. Two statutes now work together:

• AB 671 (2019) / Gov. Code §65852.23 — Required every California jurisdiction to develop and adopt a legalization plan for unpermitted ADUs. This is the earlier statute; many CODE360 case files, and many county planning-department documents, still cite AB 671 as the pathway.

• AB 2533 (2024) / Gov. Code §66332.5 — Strengthened and expanded the amnesty framework, added the express impact-fee waiver, tightened the standards a jurisdiction can enforce against an amnesty application, and gave homeowners a firmer legal footing.

In practice, if you're applying today, the operative citation is AB 2533. But the ABAG/MTC guidance memo to Bay Area jurisdictions (updated 2024) treats the two as a continuous framework — and Napa County, like most California counties, accepts amnesty applications under the combined pathway.

What the County Cannot Deny You For

This is the core of the law, and the part most homeowners don't realize is protected.

Under AB 2533 / Gov. Code §66332.5, the local jurisdiction cannot deny an amnesty application because of:

1. Lack of construction permits at the time the unit was built

2. Noncompliance with the building code that was in effect when the unit was built

3. Noncompliance with the local ADU development standards currently on the books (size, setback, height, parking)

That last point matters. If your unit is 1,240 square feet and your county's ADU ordinance caps detached ADUs at 1,200 square feet, AB 2533 says the county cannot deny amnesty for the 40-square-foot overage. Same for setbacks, same for height. The amnesty pathway is expressly designed to legalize units that don't meet current local standards.

What the County Can Still Enforce

The tradeoff is that the unit still has to be safe.

Under Health & Safety Code §17920.3, "substandard housing" is defined by a specific list of conditions: inadequate sanitation, structural hazards, hazardous plumbing or electrical wiring, inadequate weather protection, fire hazards, and so on. AB 2533 preserves the jurisdiction's authority to require correction of these conditions before issuing the legalization permit.

In practical terms, this means the amnesty pathway typically requires:

• Fire and life safety compliance — interconnected smoke and CO alarms, egress windows in sleeping rooms, and 1-hour fire separation between an ADU and any garage below (CRC R302.6)

• Electrical compliance to the California Electrical Code in effect at the time of legalization (GFCI, AFCI, weatherproof exterior covers, dead-front seating on the service panel)

• Plumbing compliance — accessible gas shutoffs, T&P discharge on tankless water heaters properly routed, seismic strapping

• Mechanical/HVAC — vented exhaust at baths and range, adequate combustion air

• Structural — the framing must be adequate for residential live and dead loads (40 psf live plus finishes for an R-3 occupancy), which matters when the original structure was framed as a garage or U-occupancy

• Wildland-Urban Interface (WUI) compliance in high fire hazard areas — ember-resistant vents, exterior cladding, Class A roof (CRC R337)

• Defensible space inspection in WUI zones

None of these are optional. All of them are pricing exposure. But they're the actual work — not the punitive fee schedule you'd face outside the amnesty pathway.

The Impact-Fee Waiver — Real Numbers

This is where AB 2533 puts money back in the homeowner's pocket.

Impact fees are one-time fees local jurisdictions charge new development to pay for schools, parks, roads, and affordable housing. For a new ADU built today in a California county, impact fees can total anywhere from a few thousand to well over $20,000 depending on the jurisdiction, the size of the unit, and the local fee schedule.

Under AB 2533, all impact fee categories are waived on the legalization application — including the Affordable Housing Impact Fee that many counties have recently adopted. In Napa County's case, the Affordable Housing Impact Fee (adopted October 21, 2025; effective January 16, 2026) would otherwise assess an ADU over 750 square feet proportionately to the primary residence. Under AB 2533, waived.

Standard permitting, plan check, and inspection fees still apply. So do state surcharges (SMIP, Building Standards, CASp).

The One Fee AB 2533 Doesn't Categorically Waive

Here's the pitfall.

Under California Building Code §109.4, when a jurisdiction discovers work performed without a required permit, it can charge a Code Investigation Fee — commonly 400% of the standard building inspection fee — as a penalty. This is not an impact fee. AB 2533 does not categorically waive it.

Some jurisdictions apply discretion under a voluntary-disclosure policy to reduce or waive the Code Investigation Fee when a homeowner comes forward on their own to legalize an unpermitted ADU. Others do not, and their staff have no administrative authority to negotiate.

This creates a real financial spread on any legalization project. On a recent Napa County case, CODE360 modeled the exposure in two scenarios:

• Scenario A (400% penalty applied): Code Investigation Fee of $4,800–$8,800 on top of ~$5,930–$11,395 in standard county fees

• Scenario B (penalty reduced or waived under voluntary-disclosure discretion): Code Investigation Fee of $0–$4,800 on the same base

That's a five-figure delta on a single line item — and it's the reason we recommend a Pre-Application meeting with the county before any amnesty application is filed. Getting the Fire Marshal, Planning, Building, and Environmental Health in one room to preview the scope, and to signal voluntary disclosure, changes the county's posture on the penalty in a way that a cold application does not.

What the Full Legalization Actually Looks Like

For a typical unpermitted-ADU legalization under AB 2533 in Napa County, the sequence is:

1. Pre-Application meeting with the county's multi-division team ($2,500–$5,000)

2. As-built plan set — floor plan, electrical, plumbing, mechanical, structural assessment (often LIDAR-scanned and CAD-converted; $1,200 pass-through in the CODE360 model)

3. Corrective construction by licensed trades on the specific findings from the inspection

4. Owner affidavit + permit application filed under the amnesty pathway

5. Plan check and corrections — typically 3–6 months in current Napa workload

6. Inspections across trades

7. Final — the unit is now a legal, permitted, insurable ADU on title

On the Napa County case referenced above, the all-in order-of-magnitude total came out to $26,670–$62,345 across four scenarios — meaningfully less than the cost of demolishing the unit, and orders of magnitude less than the value the legal ADU adds to the property.

If You Have Unpermitted Living Space, What to Do Next

• Don't just leave it. Every year the unit exists without a permit, the exposure grows: insurance, financing, resale disclosure, and code enforcement risk.

• Don't apply cold. Filing a permit application without preparation often maximizes the county's discretion against you, especially on the 400% Code Investigation Fee.

• Do a documented review. Pull the property's permit history, the original construction date, and any prior owner disclosures. Confirm the unit predates 1/1/2020 to qualify under AB 2533.

• Do a Pre-Application meeting. Ideally with a code-compliance consultant who has walked the county's amnesty pathway before.

• Do the math on both scenarios. With and without the 400% penalty, so you know your real range.

CODE360, LLC handles unpermitted ADU legalization under AB 671 and AB 2533 across Napa, Solano, and surrounding Northern California counties. If you have an unpermitted unit and want to understand your exposure and options, reach out at codehelpnapa.com or call (707) 637-7066.