Maybe you inherited the house and the converted garage was already there. Maybe you bought it that way and the listing called it a "bonus room." Maybe you did the work yourself in 2014 and never pulled a permit because the job seemed small at the time.
However it happened, you now own something that exists in real life but not in your city's records — and you have probably been told that fixing it means demolition, fines, or both.
That has not been true in California since January 1, 2025.
Assembly Bill 2533 created a statewide amnesty path for unpermitted accessory dwelling units and junior ADUs. The City of Milpitas fact sheet on AB 2533 states the core of it plainly: for a unit built before January 1, 2020, a local agency cannot deny a permit simply because the unit violates California building standards or does not comply with local ADU rules. The city also cannot charge impact fees or utility connection charges to legalize it, except where infrastructure work is genuinely required for health and safety.
Read that again, because it inverts what most homeowners assume. The default is no longer "the city can make you tear it out." Under the amnesty, the city is required to issue the permit unless it makes a specific finding that your unit is substandard in a way that threatens health and safety.
The Town of Colma's AB 2533 page spells out the practical effect: permit issuance is not contingent on current development standards, so setbacks, height, and size limits that would sink a new-construction proposal do not disqualify an existing pre-2020 unit.
Three things determine eligibility.
The unit was built or converted before January 1, 2020. This is the threshold that matters most, and it is on you to prove. Regional guidance published by MTC and ABAG in March 2026 notes that state law does not dictate what evidence homeowners must provide, leaving cities to set their own accepted list. Colma's published list includes county assessor records, escrow and disclosure documents from when you bought, prior building or planning records, insurance documents, notarized letters from previous owners or tenants, and dated photographs. Utility connection records and historical satellite imagery are also commonly accepted.
It is a dwelling unit, not just extra space. The amnesty covers ADUs and junior ADUs — a converted garage with a kitchen and bathroom, a backyard cottage, a basement apartment. An unpermitted family room addition is a different problem with a different (and less forgiving) path.
It is not "substandard" under Health and Safety Code Section 17920.3. This is the one real disqualifier. It means serious hazards, not imperfections. Missing smoke detectors, outlets that need GFCI protection, or an undersized egress window are things you fix during the process — they do not lock you out of it.
AB 2533 also lets you commission a confidential third-party inspection by a licensed design professional or general contractor before you ever file anything, so you can learn what you are dealing with without opening a case against yourself.
There is a second, lesser-known provision. Under Health and Safety Code Section 17980.12, an owner who receives a notice to correct violations on an eligible ADU can apply to have enforcement delayed for five years, on the basis that correcting the violation is not necessary to protect health and safety. The statute currently sunsets on January 1, 2035.
Two honest caveats. A delay is not a permit — the ABAG guidance is explicit that this pathway does not waive the permits, penalties, or fees required to legalize the structure later. And the five-year clock does not improve your position when you sell, refinance, or file an insurance claim.
Most homeowners in this situation are not being reckless. They are managing a risk they hope never surfaces. It is worth being clear-eyed about where it surfaces.
Insurance. California homeowner policies commonly exclude damage to unpermitted structures, and an undisclosed unit can complicate a claim on the main house. That is a bad discovery to make after a fire. We walk through the broader coverage questions in does homeowners insurance cover a remodel.
Appraisals and financing. Appraisers exclude unpermitted living space from gross living area, and lenders compare your layout against county records. Unpermitted square footage does not count toward your home's appraised value, which quietly caps what you can borrow against it and what a financed buyer can pay.
The sale. California Civil Code Section 1102 requires sellers to disclose known material facts, and unpermitted work is squarely within that. The disclosure itself rarely kills a deal. Discovery during escrow does, because it arrives as a surprise with a deadline attached.
Enforcement. A neighbor complaint can start a code case, and when a complaint surfaces an unpermitted unit, assessors can pursue back-assessment. Legalizing on your schedule is materially different from legalizing on a code officer's.
This is the fear that keeps units unpermitted for decades, so here is the honest version.
Yes, legalizing puts the unit on the assessment roll. No, it does not reassess your whole property. Under Proposition 13, new construction is assessed incrementally — the county adds the value of the newly permitted improvement while your existing base year value on the rest of the property stays put. Your Prop 13 basis on the house is not disturbed.
For most Bay Area owners the annual increase is a fraction of what the legalized unit produces in rent or adds at sale. And the alternative is not "no reassessment forever" — it is reassessment later, on someone else's timing, potentially with back-assessment attached. We cover the mechanics of what does and does not trigger reassessment in does remodeling raise your property taxes in the Bay Area.
A few situations where the answer is genuinely no, or not yet:
The state built the framework. Cities execute it, and they are not executing it identically. Milpitas and Colma have published homeowner-facing guidance; other jurisdictions in Santa Clara, Alameda, and San Mateo counties are handling legalization through their standard permit counters with varying documentation requirements and fee schedules. The MTC and ABAG memo exists precisely because interpretation has varied across Bay Area jurisdictions.
Practically, that means the first question is not "what does state law say" — it is "how does my city implement it." That answer determines your documentation, your inspection sequence, and your realistic timeline.
Legalization is rarely just paperwork. Most pre-2020 conversions need some combination of electrical corrections, egress windows, smoke and carbon monoxide alarms, insulation, fire separation between the unit and the main house, and sometimes plumbing or foundation work. That is real construction, and it is the part worth scoping before you decide.
Arch General Construction works on ADUs, conversions, and full-home renovations across Santa Clara, Alameda, and San Mateo counties, and you can see completed work on our projects page. If the corrections turn out to be substantial, our guide to how Bay Area homeowners pay for a major remodel covers the financing options, several of which apply here. And if the reason you are considering this is that you are weighing whether to stay and improve or sell and move, add on or move up runs the full Bay Area math.
The sequence that works: confirm the construction date and gather your proof, get the unit inspected privately so you know the real correction list, price that work, then decide. Filing first and learning the scope afterward is how people end up committed to a number they never agreed to.
If you have an unpermitted unit and want to know what legalizing it would actually involve, contact Arch General Construction. We can walk the structure and tell you what the correction list looks like before you decide whether to move forward.
A note on this article: This is general information about California housing law, not legal, tax, or real estate advice. Amnesty eligibility, documentation requirements, and fees vary by jurisdiction and change over time — confirm current requirements with your city's building department. Before selling a home with unpermitted work, or before relying on a disclosure strategy, consult a California real estate attorney. For questions about how legalization would affect your assessment, contact your county assessor or a tax professional.
We're here to help you build your future. Whether you're ready to start your project or just have a few questions, our team is ready to assist. Contact us today to schedule a consultation or request more information.
Book a Consultation