ADUs
My property has an unpermitted ADU or garage conversion. Can I make it legal?
A 2024 law changed the question from “does it meet today's code” to “is it safe to live in.” Here is what that means at the inspection, and where the law stops helping.
Usually yes, if the unit was built before 1 January 2020. Since 1 January 2025, state law (AB 2533, now Government Code §66311.7) bars a city from denying a permit for an unpermitted ADU or JADU of that age just because it breaks today's building code or the local ADU rules, and it waives penalties and impact fees. What the city can still require is that you fix anything that makes the unit substandard under Health and Safety Code §17920.3, which is the life-safety list: exits, smoke and CO alarms, wiring, gas, structure and fire separation.
What the law says, in plain terms
AB 2533 (Carrillo, Chapter 834 of 2024) took effect on 1 January 2025. It rewrote one section of the Government Code, the one that protects older unpermitted ADUs, and moved the cutoff date from 2018 to 2020. On 1 January 2026 a second bill, SB 543, renumbered that section from §66332 to §66311.7 without changing the rules in it. So you will see both numbers online, and they describe the same law. The text is short and worth reading: AB 2533 as chaptered and SB 543 section 9.
| Question | What the statute says |
|---|---|
| Which units qualify? | An unpermitted ADU or junior ADU (JADU) constructed before 1 January 2020. |
| Can the city deny the permit? | Not because the unit violates building standards, and not because it breaks the state or local ADU rules (size, setbacks, height, parking). It may deny only if it makes a finding that correcting the violation is necessary to meet the substandard-building standards in Health and Safety Code §17920.3. |
| Is there a carve-out? | Yes. The protection does not apply to a building that is deemed substandard under §17920.3. In practice that means the substandard items get fixed as part of the permit. |
| Impact fees? | None, and no connection or capacity charges, unless utility infrastructure is needed to cure a §17920.3 condition and the fee is otherwise authorized by state ADU law. |
| Penalties? | If the inspector finds health and safety problems, the city may not penalize you for having the unit and must approve the permits needed to correct them. |
| What must the city publish? | A checklist of the §17920.3 conditions, and notice that before applying you may get a confidential third-party code inspection from a licensed contractor. |
Many summaries say AB 2533 created the five-year enforcement delay, or that it orders the state housing department (HCD) to write new guidance. Neither is in the bill. The delay lives in Health and Safety Code §17980.12, which a different 2024 bill (SB 1514) amended. HCD does explain AB 2533 in its March 2026 ADU Handbook, but the bill itself only amended the one Government Code section.
One more thing the statute does not do: it does not waive ordinary permit fees. San José says plainly that its standard permit fees apply, including plan check and inspections, and that its “Fee for Work Without a Permit” is not charged on a legalization.
If code enforcement found it first
A separate law covers the owner who already has a notice in hand. Under Health and Safety Code §17980.12, until 1 January 2030, an enforcement agency that issues a notice to correct a building-standards violation on an ADU built before 2020 has to say in that notice that you may ask for a delay. You apply on the agency's form. It must grant a five-year delay if it decides that correcting the violation is not necessary to protect health and safety, and it consults the fire code enforcement side before deciding. No new delays can be approved on or after 1 January 2030, though a delay approved before then runs its full term.
The delay buys time. It does not make the unit legal, and it does not reach the items that are a real hazard. Legalizing usually closes the case: San José's FAQ says an open code enforcement case limited to the unpermitted unit is closed once the legalization permit passes final inspection.
What the inspector actually looks at
This is the part that surprises people. San José describes its legalization inspection as “a safety-focused review, not a full building code compliance check,” and says only the corrections its inspector identifies are required. The yardstick is the §17920.3 list, which San José has turned into a one-page checklist in Bulletin #214. Here is what that list covers and how it tends to show up in a converted garage or a backyard unit.
| Item | What the checklist asks | Where it usually falls short |
|---|---|---|
| Exits and escape openings | Exits as required, and emergency escape and rescue openings where a room is used for sleeping | A bedroom whose only window is a small high garage window, or none at all |
| Smoke and CO alarms | Smoke alarms and carbon monoxide alarms installed as required | Missing, or a single battery unit in the main room |
| Wiring | Wiring that met the code when it was installed and is safe and working now; GFCI protection at bathrooms, kitchen counters and outdoor outlets | Circuits run off the garage door opener outlet, an overloaded panel, no GFCI at the sink |
| Gas, heat and venting | Mechanical equipment and vents in safe working order; permanent heat that can hold 68°F in habitable rooms | A plug-in space heater instead of permanent heat; a water heater in the living space |
| Structure | Foundation, floor, wall and roof framing adequate for the loads, plus resistance to horizontal (earthquake and wind) forces | A converted shed sitting on blocks; a roof carrying new loads it was never framed for |
| Fire separation | The fire-resistive construction the code required, maintained and increased when the use changed | An attached unit sharing an unrated wall or ceiling with the remaining garage |
| Habitability | Natural light at 8% and ventilation at 4% of floor area; rooms at least 70 sq ft and 7 ft in any direction; no dampness or visible mold | A garage slab that wicks moisture into carpet; a bedroom carved too small |
The key phrase in §17920.3 is “in effect at the time of installation.” Existing systems (wiring, plumbing, mechanical equipment, vents) that met the code when they went in, and are still in good, safe working condition, do not have to be brought up to today's code. San José's FAQ says the same thing in its own words. That single phrase is the difference between legalizing a 2012 conversion and permitting a brand-new ADU.
Item (n) of §17920.3 lists any space used for living or sleeping that was not designed or intended for it. Redwood City's Building FAQ puts it bluntly: you cannot live in, sleep in or rent your garage as a dwelling unit. So a legalization does not ask the city to accept a garage with a bed in it. The permit shows the space as a dwelling, and the corrections are what make it one.
Expect some walls to open. San José asks owners to expose the foundation in at least one location before the first inspection, which it books for 90 minutes, and says the inspector will mark further spots to open so wiring and framing can be seen. It also suggests having a licensed electrician look before you apply, and leaving those openings for the inspector so nothing is opened twice.
The as-built permit path, step by step
The details differ by city. The sequence below follows San José's published AB 2533 program, which is the most complete one in our two counties.
Prove the date
The burden is on you. San José accepts County Assessor records, older city records that mention the unit, escrow papers or a Transfer Disclosure Statement naming it, dated photos or aerial history, insurance policies, old leases, contractor invoices, and date stamps on materials or appliance serial numbers. Without proof, the unit is permitted as a new ADU under current code.
Get the pre-application inspection
Optional, confidential, and done by a licensed contractor or design professional you choose. It approves nothing. What it does is tell you what the fixes are before the city does.
Draw the as-built set
To scale: a site plan, foundation, floor and framing plans, elevations and details showing what is there now, plus the corrections. San José also wants exterior photos of every side.
Submit and pay plan check
Fire review may be added in a wildland-urban interface area or where the main house has sprinklers and the unit does not. Public Works review may be added in a flood or geologic hazard zone.
Build the corrections and inspect
Work starts once the permit is issued. If the inspector finds something new, such as a missing permanent heater or an undersized panel, San José adds it to the same permit as a revision.
Final
When the plans match the building and no substandard items remain, the inspector signs off and the unit is legal. San José says this typically takes 4 to 6 months from a complete application.
Who draws it, and when an engineer is needed
Every city page we read expects plans. San José says to hire a professional for the as-built set; Mountain View recommends a licensed architect or engineer. An as-built set documents what exists. It is not a redesign, and it rarely needs one.
An engineer comes in when structure is the open question. San José's bulletin says that if structural work is needed to correct a deficiency, structural plans and calculations are required before the permit is issued. The usual triggers we see are a footing that fails the depth or width check, a bearing wall someone removed, a second floor over a converted space, or a roof now carrying solar or a new ceiling load it was not framed for. We are builders, not designers, so we work alongside the drafter or engineer and hand them what we found when the walls were opened.
How cities in Santa Clara and San Mateo counties handle it
The statute is the same everywhere. The paperwork is not. This is what each page said when we read it on 11 October 2026; city pages change, so check yours before you draw anything.
| Jurisdiction | What its own page says |
|---|---|
| San José | A dedicated AB 2533 program run by the ADU Ally team, the Bulletin #214 checklist, as-built plans, a safety-focused inspection, and no work-without-permit fee. FAQ |
| Sunnyvale | Eligibility is worded as an ADU or JADU built “inside a permitted structure” before 1 January 2020, with reduced development standards if the unit is found safe, and a five-year deferred enforcement request through Community Development. The state statute does not use the permitted-structure phrase, so if the shell itself was never permitted, ask the city how it reads the two together. ADU page |
| Mountain View | A legalization process with no code enforcement action or penalties, for units built before 2020 with no existing permit. The page still tells owners to correct violations of current building and zoning codes, which is stricter wording than §66311.7. HCD's handbook says disputes over corrections go through the city's own appeals process. Legalize page |
| Redwood City | We found no dedicated AB 2533 page. The Building FAQ states a garage is non-habitable and cannot be used as a dwelling. Call the Building Division before you draw. Building FAQ |
| Unincorporated San Mateo County | An AB 2533 amnesty page: no impact or connection fees except for required utility work, an inspection against the County Substandard Housing Checklist, and the same application path as a new ADU. Cities inside the county run their own process. County page |
If a buyer or a lender finds it first
California sellers disclose on the Real Estate Transfer Disclosure Statement set out in Civil Code §1102.6. That paper trail cuts both ways. An old disclosure that names the unit is on San José's list of evidence that it existed before 2020, so a previous owner's paperwork may be exactly what proves your date.
Unpermitted living space may not be counted by an appraiser, which can change what a buyer's lender will finance, and insurers may treat it differently from permitted space. Those are their calls, not ours, so ask your lender and your carrier directly. What we can say is that a legalization started before you list runs on your schedule, and one started in escrow runs on the buyer's. Our guide to unpermitted work found during a sale covers the escrow side.
How we approach a legalization
The statute names a licensed contractor as someone who can do the confidential pre-application inspection. We are a licensed California General B contractor (#1112902), and that walk is where we start. We go through the unit against the §17920.3 checklist and open what the inspector will want opened. Then we write down what is there, before anyone draws a line.
From that walk we scope the corrections and price them, line by line, so you know the number before you file. Then we coordinate the as-built drawings with your drafter or engineer and pull the permit. After that we build the fixes and meet the inspector on site. Most of the cost of a legalization is in the corrections, which is why we price them from a site walk and never from a photo.
Whether your city will make a denial finding on your unit, or how a court would read the statute. That is the city's decision on your specific facts, and if a denial is disputed, an attorney is the right call. We tell you what the code says and what the building needs.
The next step is a Project Discovery Call. Bring photos of the unit and any paperwork that shows the year it was built, and tell us whether there is an open code enforcement case. That is enough for us to tell you whether the walk is worth scheduling.
Common questions
Can a California city still refuse to permit an unpermitted ADU built before 2020?
Do I have to bring an old garage conversion up to current building code?
Will I pay impact fees to legalize an unpermitted ADU in California?
What if my unpermitted ADU was built after 1 January 2020?
Does AB 2533 give me five years to fix code violations?
Where to go next
Written by the team at Elusive Construction, a licensed California general contractor (B #1112902) building in Santa Clara and San Mateo counties. General information about how residential construction works — not legal advice. For your specific contract, talk to an attorney.
Also Worth Reading
The rest of what we publish
Cost guides
What an ADU, an addition, a kitchen or a whole house actually costs here, and what moves each number.
Our own projects
Two jobs written up start to finish, including what we found once the walls were open.
Paying for it
Renovation lenders we work with. We take no referral fee, and we never quote you a rate.
Where we build
Sixteen cities across two counties, and what genuinely changes at each city line.
Have a project you want priced honestly?
Book a Project Discovery Call and we'll tell you what's realistic — scope, budget and timeline — whether or not we're the right builder for it.