How to Prove Your Unpermitted ADU Existed Before 2020 (AB 2533 Evidence Guide)

How to Prove Your Unpermitted ADU Existed Before 2020 (AB 2533 Evidence Guide)

California's AB 2533 lets you legalize an unpermitted ADU built before January 1, 2020 — but the burden of proof falls on you. If your city is asking for evidence and there are no permits on file, here's exactly where to look.

Why is the city asking for proof of conversion, not just the structure?

This is the trap most homeowners hit. AB 2533 protects unpermitted ADUs and JADUs that existed as dwelling units before January 1, 2020 — not just structures that happened to be standing. A city looking at a 2017 aerial photo can see your detached building, but that doesn't tell them whether the inside was a shed, a workshop, or a habitable unit with a kitchen and bathroom.

A dwelling, by definition, has sleeping, cooking, and sanitation facilities. So when the city says "prove the conversion," they're really asking you to show that a kitchen and bathroom existed inside that structure before 2020. That's a meaningfully harder question than "did the building exist."

The good news: you don't need a single perfect document. Cities reviewing AB 2533 applications generally accept a preponderance of evidence. Three or four reasonable pieces pointing to the same date will usually carry the day, even when no single piece is conclusive.

Where do I find historical aerial photos of my property?

Historical aerials are usually the easiest place to start. They prove the structure existed on a specific date, which is the foundation everything else builds on. Even though aerials can't show what's inside, a clear pre-2020 image of the building is a baseline most cities expect to see in the package.

Free and low-cost sources:

Google Earth Pro has a historical imagery slider that lets you scroll through annual snapshots of your property going back to the early 2000s in most California neighborhoods. It's free to download and the image dates are clearly labeled.

NETR Online's HistoricAerials.com aggregates aerial imagery from multiple government and commercial sources. Many California parcels have coverage going back to the 1940s, which is useful if your structure is genuinely old.

USGS EarthExplorer hosts federal aerial and satellite imagery, free to download with a registered account. Useful when you need an officially-sourced image rather than a screenshot.

Nearmap is a paid service with very high-resolution imagery in California, often updated several times per year. If the cheaper sources aren't producing a clean image, this is worth the subscription cost for one month.

Your county GIS portal often has its own aerial archive. Santa Clara County, for example, maintains historical aerials accessible through its mapping system.

When you save an aerial, screenshot the full window including the date label. That timestamp is what makes the screenshot evidence rather than just a picture.

Stuck on what evidence the city will actually accept?

How do I request the County Assessor's property record?

The County Assessor often picks up structural changes that the city's planning department missed. A reassessment tied to "new construction," "addition," or a reclassification from "shed" to "second unit" is direct evidence of the conversion date — sometimes the strongest piece of paper in the entire package.

What you're asking for is the appraisal record or property characteristics file for your parcel. This typically includes the appraiser's notes, dated sketches with dimensions, square footage breakdowns by structure type, inspection dates, and historical reassessments tied to specific construction events.

In Santa Clara County, the Assessor's office is at 130 West Tasman Drive in San Jose. There are three ways to make the request:

Call 408-299-5500 and ask for the appraiser assigned to the area where your property is located. Each part of the county is covered by a specific appraiser who knows the neighborhood and can often tell you what's in the file before you make a trip. Frame it as a collaborative question: "I'm legalizing an unpermitted ADU under AB 2533 and need to establish the conversion date — can you tell me what your file shows?"

Walk in with the address or APN. The public counter will pull the file and let you review it on the spot, with a per-page copy charge for anything you want reproduced. Bring photo ID. If you're not the owner of record, bring written authorization.

File a written Public Records Act request citing California Government Code § 7920 et seq. Specify the APN and ask for: the full appraisal record including all historical entries and field notes, any dated building sketches, the reassessment history with reasons for value changes, and any records reflecting reclassification of accessory structures to habitable use.

If the Assessor's file shows no reassessment for conversion, that's informative too — it tells you the conversion was never picked up, which is consistent with a fully undocumented unpermitted unit. In that case you'll need to lean harder on the other evidence sources below.

Can old MLS listings prove when my ADU was converted?

Often yes — and this is one of the highest-leverage moves you can make. If the property has changed hands at any point in the last decade or two, prior MLS listings may contain interior photos, square footage breakdowns, and listing remarks that document the ADU as a dwelling on a specific date.

What to look for in old listings:

Interior photos showing a kitchen, bathroom, or bedroom inside the ADU. Square footage breakdowns that list the unit as living space rather than a shed or garage. Listing remarks describing it as a "guest house," "in-law suite," "studio with kitchenette," "second unit," or "permitted status unknown." Rental income disclosures or mentions of a tenant in place.

MLS systems like Matrix retain expired listings going back many years. Listings are timestamped, which makes them strong contemporaneous evidence. The catch is that public sites like Zillow and Redfin only show a fraction of the historical listing data — the photos and remarks from old listings often disappear from public view.

The fix is to ask a real estate agent with MLS access to pull the full listing history for the property, including all archived photos and remarks. Most agents will do this as a favor for past clients or as part of an estimate. Save everything they send you, including the listing date and the agent's name on the listing — that's what authenticates it.

The same approach works for finding disclosure forms (TDS, SPQ, NHD) from prior sales. These aren't part of the public record, but the listing brokerage from that prior sale is required to retain transaction files for at least three years and often keeps them five to seven years on platforms like Glide, zipForm, or Skyslope. A polite request, especially if you can identify the listing agent, sometimes produces a copy of the disclosure package — which may explicitly describe the ADU.

How do I find archived Craigslist or Zillow rental listings?

If the ADU was ever rented, there's a good chance the listing was archived somewhere even if the original page is long gone. The Internet Archive's Wayback Machine at web.archive.org periodically saves snapshots of public web pages, including expired rental listings.

For Craigslist (where listings expire and disappear quickly), try these:

Search the property address directly at web.archive.org. The site has a full-text search that sometimes catches archived listings mentioning a specific address. Run a Google site-restricted search like site:web.archive.org "1234 Main St" craigslist — this often surfaces results the Wayback Machine's own search misses. If you know the prior owner's name, try that plus "craigslist" plus your city.

For Zillow, Trulia, Hotpads, Apartments.com, and Realtor.com, the workflow is more reliable. Find your property's URL on each platform, then paste it into the Wayback Machine. You'll see a calendar of all snapshots taken of that page, sometimes going back ten years. Click through snapshots from 2015–2019 and look for "Price History," "Rental History," or descriptions mentioning the ADU.

For Airbnb and VRBO, archiving is harder because listings use unique IDs and don't show full addresses publicly. Try searching the property address plus "airbnb" in the Wayback Machine — sometimes hosts included neighborhood landmarks or partial addresses that got indexed. AirDNA and similar third-party services sell historical short-term rental reports for specific addresses if you really need the data.

When you find a useful snapshot, do two things immediately. Save the full Wayback Machine URL — the date is embedded in it (e.g., web.archive.org/web/20180614/...). And screenshot the page including the Wayback Machine timestamp banner at the top. That banner is what makes the screenshot self-authenticating to the city.

Also worth checking: archive.today (also reachable at archive.ph) is a separate archiving service with different coverage. If the Wayback Machine comes up empty for a particular page, try archive.today using the same URL.

What other evidence do cities accept?

If aerials, Assessor records, MLS history, and rental archives don't get you all the way there, several other sources can fill in the gaps. Cities looking at AB 2533 applications generally accept any of these as part of an evidence package:

Utility records. A kitchen and bathroom mean water and sewer connections. PG&E may have records of a panel upgrade or sub-panel installation at the structure. Your water utility may show a service upgrade, additional fixture units, or a separate sub-meter. Sewer lateral records — often held by the city's public works department, separate from planning — can show when additional fixtures were tied in.

Insurance documents. Homeowner's policies typically schedule the main dwelling and "other structures" separately. If a prior owner's policy specifically listed the ADU as a dwelling or guest house rather than a shed or detached garage, that's third-party documentation of its use. Prior owners may still have declarations pages, or their broker may have records.

Contractor and trade records. Even unpermitted work generates paper. Plumbers, electricians, HVAC technicians, kitchen cabinet installers, countertop fabricators, tile suppliers, and appliance retailers like Home Depot and Lowe's often keep purchase records tied to a property address. If you know who the prior owner was, ask them — many homeowners save receipts longer than you'd expect.

Lease agreements and rental records. Written leases, payment records, tenant declarations. If the unit was rented, even informally to a family member, there's likely a paper trail somewhere.

Tax records. If the prior owner reported rental income on Schedule E of their federal return, that's documentation of dwelling use. They obviously won't share their returns, but a sworn declaration referencing the years they rented the unit serves the same purpose.

Sworn declarations from prior owners, neighbors, or tenants. These carry more weight than people assume, especially when paired with even one piece of paper. A declaration saying "I converted the structure in 2012, added a kitchen and bathroom, and rented it from 2013 to 2018" — combined with a single utility bill, insurance page, or contractor receipt — is often enough.

The single highest-value move, if you haven't done it yet, is to track down the prior owner. The county recorder will tell you who owned the property in past transactions. A polite letter explaining you're trying to legalize the ADU under AB 2533 and asking for any documentation they kept gets a yes more often than not. People generally want to help, and they're not on the hook for anything by sharing.

Quick questions on AB 2533 evidence

What if I can't prove conversion happened before 2020?

AB 2533 isn't your only option. Government Code 65852.23 and the broader statewide ADU statutes still allow legalization through code compliance. You'd lose AB 2533's specific protections against certain code requirements, but legalization is still on the table.

Do I really need a sworn declaration, or is a regular letter enough?

Sworn declarations carry significantly more weight because they're signed under penalty of perjury. Most cities will accept a notarized statement on a standard declaration form. Your local planning department can usually provide a template, or any title company can notarize one for a small fee.

Can the city deny my application if my evidence is "good but not perfect"?

AB 2533 limits what cities can deny based on. They can't refuse a permit purely because of building code violations unless the unit is substandard under Health and Safety Code Section 17920.3. On the evidence-of-existence question, most planners apply a preponderance standard rather than demanding certainty.

How long do I have to gather evidence?

There's no hard deadline on assembling your package, but be aware that evidence sources don't last forever. Brokerages purge transaction files after their retention period. Wayback Machine snapshots can be removed at the request of site owners. Prior owners move and become harder to locate. The sooner you start, the more is available.

Can HomeWiP help with the evidence-gathering process?

Yes — we work with Bay Area homeowners on ADU legalization regularly, including the proof-of-existence question under AB 2533. We can help identify which sources are likely to produce results for your specific property and walk you through what the city in your jurisdiction tends to accept.

Need help building an evidence package the city will accept?

Book a Free Call