Bonita resident Stephen Stonehouse told county planning commissioners last December that he had finished an accessory dwelling unit on his property in 2022. He built it planning to split the lot someday and convert the ADU into a condo. As reported by the San Diego Union-Tribune, the idea was "to use it for ourselves when we get old, and sell the main house."
Under County rules, that plan is now possible. San Diego County's version of Assembly Bill 1033 took effect April 4, 2026. It lets owners in unincorporated communities sell an ADU separately from the main house through a condominium conversion. A second set of rules took effect September 18. For anyone comparing Bonita lots, the new rules raise a question the listing will not answer. The option belongs to individual parcels, and in Bonita two separate gates decide which parcels get it.
Gate One: Which Government the Parcel Answers To
Bonita is a place name and a ZIP code, and neither one tells you who has jurisdiction. The County's Sweetwater Community Plan notes that the central section of the Bonita Road valley was annexed into Chula Vista. It also places commercial areas along Bonita Road inside the City. The unincorporated Sweetwater planning area is the land south of SR-54, east of I-805 and north of Chula Vista.
That line matters because AB 1033 is optional for each city or county. State Government Code § 66342 says a local agency may adopt an ordinance allowing separate condo sales. Nothing happens automatically. The County adopted one. Chula Vista's local ADU sections, CVMC 19.58.022 and 19.58.023, are now marked "Repealed" under Ordinance 3592, which the City Council acted on April 15, 2025. The City's ADU page points to the state Government Code and names no local condo-sale ordinance. We found no sign that Chula Vista has opted in. Anyone counting on a separate ADU sale on a City parcel should confirm the current rules with the City directly.
To check a parcel, open the County's Jurisdiction Finder, a SANDAG map. Turn on the "Jurisdictions" layer and search the address. It takes about a minute, and it tells you which ADU rules apply to that address.
Gate Two: Gallons Per Day
Clearing the first gate puts a parcel under County rules. In the custom-home parts of Bonita, that usually means County septic rules too. The Sweetwater plan names four areas zoned at one home per one, two or four acres. It describes them as usually on septic, and sometimes keeping horses. The plan does not name those areas by subdivision. That's why the ZIP code can't tell you whether a lot is on septic, and neither can a neighborhood name.
On a septic lot, the County's Local Agency Management Program, or LAMP, sets the size of any ADU. The current version took effect February 1, 2025, and added a specific ADU pathway. Under LAMP section 3.7.9.4, a standard septic system and dispersal field can handle 900 gallons a day for the whole parcel. That works out to a six-bedroom equivalent for the main house and the ADU combined.
Do the math on a typical lot. A four-bedroom house already uses four of the six bedroom equivalents, so a standard system leaves room for roughly a two-bedroom ADU. A five-bedroom house leaves room for one bedroom. The cap also comes with a land requirement. The parcel needs a reserve area big enough to replace the entire dispersal field for both the house and the ADU. On a big lot, some of the acreage that looks open may already be committed to that reserve.
| Parcel situation | What the County rules say |
|---|---|
| Standard septic system | Up to 900 gal/day for the parcel, a six-bedroom equivalent, plus a full replacement reserve area |
| Septic with supplemental treatment for nitrogen reduction and drip dispersal | Up to 1,500 gal/day, a ten-bedroom equivalent, plus a full replacement reserve area |
| Existing system too small for the ADU | More tank capacity and dispersal area must be added to the existing system, or a new system installed |
| Sewer abutting or within 200 feet, parcel inside or annexed to a sewer district, and no easement needed to connect | New or replacement septic generally prohibited |
The sewer row has an exception. A replacement septic system may still be allowed if the sewer connection fees and construction would cost more than twice as much as the septic system, and a compliant system can be installed. If the County lacks the soil data it needs, it may require soil profiles, percolation tests or groundwater tests. On a septic parcel, any building permit or change in use also requires an OWTS Layout Report showing that the existing and proposed systems meet the LAMP. That report is generally approved before the permit is issued.
Put the two gates together and you get the real comparison. One 91902 lot can be in the County with septic capacity to spare. Another can have a five-bedroom house that already uses most of its 900 gallons. A third can sit across the City line. All three may look like "Bonita acreage with ADU potential" in a listing.
What the Septic System Costs
Septic work also has its own price list. One San Diego County septic company, All-American Septic Pumping, lists residential pumping starting around $500. The final price depends on tank size, truck access and whether the lids are already uncovered. The same company offers escrow inspections. Lanik Septic, a contractor serving San Diego County, estimated California costs as of April 2026. Replacing a conventional system ran $10,000 to $20,000. Replacing only the tank ran $3,000 to $7,000, and a straightforward drain-field replacement ran $5,000 to $15,000. Those are statewide estimates, not Bonita quotes. Soils, engineering, access and system design can push a real bid in either direction.
For buyers, the County's buyer guidance suggests having a licensed contractor check whether pumping is due when the seller has no maintenance records. Many parcels have septic records available. The County's septic records page explains how to find maps and plans through the environmental health document library.
Who Can Buy the ADU
A lot that clears both gates still faces the County's newest layer of rules. On August 19, 2026, the Board of Supervisors voted 5–0 to adopt Ordinance No. 11016, which the Planning Commission had recommended in June. Since September 18, according to the County's ADU ordinance page, properties with ADU condos must meet three requirements:
- Right of first refusal. Each condo owner on the lot sets up a contract with an existing tenant or the other owner. That party gets the right to buy by matching a future offer.
- Owner-occupancy affidavit. New buyers of an ADU condo sign a statement that they or a family member intend to live in the unit as a primary residence for a set period.
- Public posting period. Every time the unit is listed, it must be publicly posted for a set period, with a disclosure that it is offered to buyers who plan to live there or house a family member.
When the Planning Commission voted in June, commissioners preferred a 30-day matching period, one year of owner occupancy and a 30-day listing period. In practice, the people who can buy a Bonita ADU condo are owner-occupants and their families, and a tenant or the other condo owner on the same lot gets a chance to match any offer. The County's ADU Condo Guidance & Checklist covers eligibility. It works alongside a Tentative Parcel Map or Tentative Map application and does not replace either one. The County's own staff report notes that projects still have to meet existing building, grading, environmental, health, safety and subdivision requirements. That list includes the septic rules from gate two.
Countywide prices show why the plan Stonehouse described appeals to owners. SDAR's September 2026 report put the San Diego County median at $1,079,000 for detached homes and $670,000 for attached homes. Those numbers cover the whole county, not Bonita, and an ADU condo is its own product. Still, a gap that large shows why owners might want to keep the smaller unit and sell the main house, and why the rules about who can buy matter so much.
Horse Zoning Is a Separate Check
Bonita's equestrian reputation gets folded into the same "big lot, lots of options" pitch, but it falls under a different part of the code. The Sweetwater plan describes most subdivisions there as having open space, horses and larger lots, often on private roads. Under the County's animal regulations, what animals a parcel can keep depends on its zone designator. Horse keeping and stables are allowed only under certain designators, and some uses need a zoning verification, an administrative permit or a major use permit. On a septic lot, the septic reserve area, an ADU and any stable or corral all need space. Checking the animal designator and the reserve area at the same time shows how much of the acreage is really free to use.
Quick Answers
Does the County program cover attached ADUs or only detached ones? County staff first recommended limiting it to detached ADUs. Planning commissioners pushed for attached and detached alike, the Union-Tribune reported. In March, the Board adopted the version the County describes as giving the most flexibility in the number and types of ADUs that can be sold separately.
How common are ADUs in the unincorporated county? ADUs accounted for 1,552 residential building permits in unincorporated areas from 2021 through 2024, according to county housing data cited by the Union-Tribune.
Where do I start on a specific Bonita lot? Check the jurisdiction with the SANDAG finder first, then look up the County's septic records for the parcel. Those two answers tell you which of the rules above apply.
This post is general information, not legal, tax or financial advice. Before you make an offer or start drawings, confirm your parcel's situation with the County, the City, a licensed septic professional or an attorney.
If you own in Bonita and want to know how jurisdiction, septic capacity and the new ADU condo rules affect your lot's value, The Dream Homes Team will look at your specific parcel. Request a Free Home Valuation and we'll start with the questions above.
