One of our clients finished a 1,200-square-foot detached ADU in El Cajon last fall. The homeowner originally planned to rent it long-term, lock in some passive income, and eventually hand the whole property to her daughter. Then on March 4, 2026, the San Diego County Board of Supervisors voted unanimously to implement AB 1033—the state law that allows ADU owners to split off and sell the accessory unit as its own condominium. The rule went into effect April 4, 2026. The homeowner called us the next week: could she sell the ADU separately, recover her construction capital now, and keep the main house? Yes. The financing math just changed.
What AB 1033 Does in San Diego County
AB 1033 is a state statute. San Diego County's March 4 vote and April 4 effective date mean unincorporated areas of the county now permit separate sale of ADUs through a condominium conversion process. You build an ADU on your single-family lot, record a condo map that splits the parcel into two legal units, and sell the ADU to a buyer who gets a standalone mortgage. The main house and the ADU become separately owned condos sharing the underlying land parcel.
Before April 4, an ADU in unincorporated San Diego County was tied to the primary residence. You could rent it, you could live in it, but you couldn't sell it separately. The buyer of the main house got the ADU as part of the deal, whether they wanted it or not. AB 1033 removes that restriction in jurisdictions that adopt it, and San Diego County is one of the first to publish a full implementation pathway.
The county posted an "ADU Condo Guidance & Checklist" to help applicants determine whether their unit qualifies for separate sale. The checklist walks you through Section 6156.x of the zoning ordinance and coordinates the tentative-map process with the condo-conversion workflow. If you're drawing plans for a detached ADU in unincorporated San Diego County today, your client may ask whether the unit can be sold separately. The answer is yes, if they follow the condo-map process.
Why This Matters for Spec ADU Builders
The separate-sale option changes the investment thesis. A homeowner who spends $250,000 building a detached ADU can now sell it for, say, $320,000 and recover capital in months instead of years. The buyer—often a first-time purchaser priced out of single-family homes—gets a mortgage, moves in, and owns real property. The seller keeps the main house and reinvests the proceeds. That cycle didn't exist before April 4.
We've seen interest from small-scale spec builders who want to acquire single-family lots, build an ADU, split the parcel, and sell the ADU to one buyer and the main house to another. The pro forma depends on how quickly you can move through the tentative-map and final-map process, but the county's checklist suggests the pathway is navigable if you coordinate survey, title, and planning early.
Lenders offering ADU construction loans care about exit strategy. If the borrower can sell the ADU separately and pay off the loan faster, the risk profile changes. We've had two conversations with construction-loan officers in San Diego in the past month asking whether we can confirm on permit sets that the ADU qualifies for AB 1033 condo conversion. The answer is: we can design to zoning-ordinance standards, but the applicant has to file the tentative map and get county approval. The permit set and the condo map are separate processes, and both have to close before the sale can happen.
The June 12 Planning Commission Meeting
San Diego County isn't done tweaking the rules. On June 12, 2026, the Planning Commission will consider additional amendments "to encourage owner occupancy." The county released draft options for public feedback between May 1 and May 31, 2026, but we don't yet know what those amendments will say. The phrase "encourage owner occupancy" could mean a lot of things: an owner-occupancy requirement for the first year, a priority-processing track for owner-occupants, or a fee waiver for people who live in either the main house or the ADU.
If you're a homeowner planning to build an ADU and sell it immediately, watch the June 12 meeting. If the county adopts an owner-occupancy incentive—or a disincentive for immediate sale—it could affect your timeline. If you're a spec builder, same warning: the rules that went into effect April 4 may get a new layer in June.
That said, the April 4 implementation is live now, and the county's guidance materials are public. You can start the process today if your project qualifies.
What You Need to Submit
The county's ADU Condo Guidance & Checklist covers eligibility, but here's the short version:
- The ADU must be a legal accessory dwelling unit under current zoning.
- You file a tentative parcel map showing the condo boundaries.
- The map has to comply with Section 6156.x of the zoning ordinance and the county's subdivision standards.
- You coordinate with the county surveyor, planning, and—if there are utility easements or shared infrastructure—public works.
- Once the tentative map is approved, you record a final map and the ADU becomes a separately saleable condo unit.
We've drawn permit sets for detached ADUs that later became candidates for AB 1033 condo conversion, and the biggest coordination challenge is utility service. If the ADU shares a water meter, sewer lateral, or electrical service with the main house, you need to either split those services or set up a shared-facilities agreement before the condo map is recorded. The county won't approve a final map if the utilities aren't clearly divided or shared under a legal easement.
If you're working with a civil engineer on grading and drainage, loop them in early. The tentative-map submittal often requires a preliminary title report, a boundary survey, and a utility plan. The architectural permit set we produce covers building code and zoning, but it doesn't replace the surveyor's work on the parcel map.
Who This Opens the Door For
First-time homebuyers priced out of single-family homes in San Diego County now have a new entry point. A 1,000-square-foot detached ADU in a decent neighborhood might sell for $280,000 to $350,000—still expensive, but $200,000 less than a comparable single-family house. The buyer gets a mortgage, builds equity, and owns real property. That's a different market than the rental-ADU market, and it's one reason the state passed AB 1033 in the first place.
Homeowners with equity but no cash flow also benefit. If you own a house worth $800,000 but you're retired and can't qualify for a construction loan, you might partner with an investor who funds the ADU build in exchange for the right to buy the ADU at a set price once it's finished. The investor files the tentative map, you keep the main house, and both parties walk away with real property. We've seen two deals structured that way in the past three months, both in unincorporated San Diego County.
Spec builders and small developers looking for lower-cost inventory are watching AB 1033 closely. Building a detached ADU on an existing lot is faster and cheaper than subdividing raw land, and the separate-sale option means you're not stuck holding a rental property if the market softens. The risk is that the June 12 Planning Commission meeting could add restrictions, so anyone launching a spec ADU project in the next sixty days should plan for the possibility that the rules change mid-stream.
What Happens in Other California Jurisdictions
AB 1033 is a state law, but implementation is local. San Diego County adopted it April 4. Other jurisdictions—incorporated cities, other counties—can adopt it or ignore it. The City of San Diego (separate from the county) hasn't published an AB 1033 implementation plan as of this writing. Same with Los Angeles County, Orange County, and most of the Central Valley.
If you're drawing ADU plans for a project in California outside unincorporated San Diego County, confirm whether the local jurisdiction has adopted AB 1033. If it hasn't, the ADU can't be sold separately, and your client's financing strategy changes accordingly.
We expect more jurisdictions to adopt AB 1033 over the next twelve months, especially if the April 4 rollout in San Diego County goes smoothly. But until your AHJ publishes an ordinance and a submittal checklist, the separate-sale option doesn't exist, even though the state law is on the books.
Next Steps
If you're a homeowner or investor in unincorporated San Diego County planning an ADU build, download the county's ADU Condo Guidance & Checklist and confirm that your project qualifies for separate sale. If you're working with a lender, show them the checklist and ask whether they'll underwrite a construction loan with AB 1033 conversion as the exit strategy. If you're a spec builder, line up a surveyor and a civil engineer who understand the tentative-map process, because the architectural permit set is only half the puzzle.
And watch the June 12 Planning Commission meeting. The rules that went into effect April 4 are live, but they may not be final.
If you're starting an ADU project in San Diego County and want to confirm your design qualifies for AB 1033 condo conversion, reach out. We'll coordinate with your surveyor and make sure the permit set and the parcel map line up before you submit.