Bonita · Sunnyside · Sweetwater Valley · 91902 · 91908
ADU Builder in Bonita, CA
Most of Bonita sits outside any city, so the County of San Diego decides what you can build out back. Some annexed streets answer to Chula Vista instead. Settle that first; on a horse property or hillside lot, septic and the long trench to the house come next.
Utility pipe on siteShort answer
On unincorporated Bonita land, County Planning & Development Services (PDS) approves an ADU with a building permit and no hearing. A detached unit can be 1,200 sq ft no matter how big the house is, and an attached unit can be half the house, capped at 1,200 sq ft. The rules are in Section 6156 of the County Zoning Ordinance. On a septic lot, Environmental Health must approve a septic layout before PDS takes the plans. Annexed Bonita-Sunnyside parcels belong to Chula Vista instead. A licensed San Diego general contractor takes Bonita requests from this site.
City or County: check before you pay for plans
A Bonita or Chula Vista mailing address does not tell you who issues the permit, because ZIP lines ignore city limits. Two checks settle it:
- County Property Summary Report. Enter your APN on the County's CitizenAccess portal. It shows jurisdiction and zoning.
- Your property tax bill. The tax rate area tells you whether the parcel is in a city or unincorporated.
Why it matters: part of Bonita-Sunnyside joined Chula Vista, and Chapter 19.72 of the Chula Vista Municipal Code (1987, amended 1988) kept the County's old Zoning Ordinance No. 5281 there as interim zoning. On those parcels City Development Services takes the permit, City fees apply, and the Chula Vista ADU rules and permit guide is the better starting point. Ask which ADU standards it applies to a 19.72 parcel.
County ADU limits in Bonita
| Item | Unincorporated Bonita (County) | City of Chula Vista |
|---|---|---|
| Detached size | 1,200 sq ft, any house size | 1,200 sq ft |
| Attached size | Up to 50% of the house, capped at 1,200 sq ft | Half the house; 850 sq ft (1 bed) or 1,000 sq ft (2+ bed) floor |
| JADU | 500 sq ft inside the house | 500 sq ft |
| Detached height | 24 ft on a single-family lot, per County bulletin PDS-PLN-611 (2022) | 16 ft, 18 ft near transit |
| Who permits | County PDS, plus Environmental Health on septic lots | Chula Vista Development Services |
| Sale apart from the house | Allowed as a condo since September 18, 2026 | Not allowed |
| Water | Sweetwater Authority or Otay Water District | Sweetwater (west) or Otay (east) |
County figures from the PDS ADU page and builder summaries of PDS-PLN-611. Chula Vista column summarizes this site's Chula Vista guides. The 24 ft figure comes from a 2022 bulletin, so confirm it with PDS before you draw a second story.
New units sit 4 ft from side and rear lines and meet the zone's front setback. Builders also report 6 ft of separation from other buildings and one parking space, tandem allowed, waived near transit or for a conversion. Rentals run 30 days or longer.
The County says state ADU law wins wherever its ordinance conflicts. On July 7, 2026 the state housing department (HCD) flagged five parts of Section 6156: size measured without the words "interior livable space," too few unit combinations on single-family lots, JADU owner occupancy beyond the shared-bath case, no ministerial path for a JADU beside an ADU, and JADU replacement parking. The County's reply was due August 6. We have not seen an amendment, so ask PDS where those points stand.
County ADU plans
PDS posts eight dwelling plans, and six of them can be built as a detached ADU:
| Plan | Size | Layout |
|---|---|---|
| A | 1,200 sq ft | 3 bed, 1 bath |
| B | 1,200 sq ft | 2 bed, 1 bath |
| C | 1,200 sq ft | 2 bed, 2 bath |
| D | 1,000 sq ft | 1 bed, 1.5 bath |
| E | 800 sq ft | 1 bed, 1 bath |
| F | 600 sq ft | 1 bed, 1 bath |
Plans G (1,728 sq ft) and H (1,500 sq ft) are for primary homes only.
Sets download as PDFs and CAD files, about 85% complete; checklist PDS 607 lists what you add, such as the site plan, energy calculations, trusses and any septic layout. Local news called them free at the 2019 launch, but the plan page lists no price today, so confirm. Only Plan F stays under the 750 sq ft impact-fee line, and all six owe school fees, so a custom 499 or 740 sq ft design can beat a ready drawing on fees.
Septic lots: Environmental Health comes first
Some Bonita parcels are sewered and others use septic. On a septic lot, County Environmental Health (DEHQ) treats the ADU as a second dwelling on the system.
Perc tests and layout
A septic professional tests the new leach area and its 100% reserve, then files a layout application.
Size the tank for both homes
DEHQ's table runs from 1,000 gallons (one bedroom in each home) to 1,500 gallons (for example, a three-bedroom house with a one- or two-bedroom ADU).
Get approval before the building permit
PDS rejects site plans missing the septic system or a well. Layout approval lasts one year.
The Chula Vista ADU cost calculator has no septic line. A San Diego builder's rough numbers: leach fields from $25,000 to $30,000, seepage pits laid horizontally from $60,000 to $70,000, three to four months of County review, and up to 10,000 sq ft of open ground.
Horse properties and the valley floor
The County calls the Sweetwater planning area a semi-rural equestrian community; its western half is mostly homes on parcels under an acre. Barns, corrals and riding rings compete with the ADU for flat ground, so put them on the site plan early.
Sweetwater Dam broke in 1906, and El Niño storms still flood the bridgeless Central Avenue river crossing. Near the river, ask PDS about flood rules before you fix a location.
Selling the ADU as a condo
Here Bonita parts ways with Chula Vista. The Board of Supervisors adopted an AB 1033 separate-sale program on March 4, 2026, and Ordinance 11016 (adopted August 19, effective September 18, 2026) wrote the sale and occupancy rules into Section 6156. A sale runs through a tentative parcel map or tentative map, with the PDS ADU Condo Guidance and Checklist. We have not read the full ordinance, so ask PDS for its conditions and budget for map fees, a survey and condo documents. Inside Chula Vista, an ADU still cannot be sold separately.
Fees on County land
- Permit and review. PDS posts no ADU total. A builder's formula (a base near $1,740 for review and $1,482 for the permit, plus well under a dollar per sq ft) works out near $3,860 at 740 sq ft and $4,260 at 1,200 sq ft. The Green Building Incentive Program may cut that.
- Impact fees. The County waiver ended January 9, 2024. Units under 750 sq ft are exempt; larger ones pay a share sized to the house. Ask PDS for the County figure, since Chula Vista's fees do not apply.
- Fire. The Bonita-Sunnyside Fire Protection District posts a fee schedule and a fire mitigation fee schedule; ask whether either reaches an ADU.
- School fees. Bonita is in Chula Vista Elementary and Sweetwater Union territory: $2.37 plus $3.01, or $5.38 per sq ft, above 500 sq ft.
- Water. Sweetwater Authority serves part of Bonita and Otay Water District the rest; your bill says which. Adding a meter brings a $6,683 Water Authority charge this year, dropping to $5,617 in 2027, on top of district fees we could not confirm.
What a Bonita ADU costs
Building costs follow the South Bay ranges in our Chula Vista calculator. On a level, sewered lot at mid finish, plan on about $327,000 for a 740 sq ft detached unit (roughly $281,000 to $373,000). Converting a 400 sq ft garage lands near $145,000 to $153,000, and a 300 sq ft JADU near $100,000.
Swap the calculator's City permit and sewer lines for the County permit and your sewer agency or septic system. At 1,200 sq ft its $484,000 west-side figure carries about $27,500 of Chula Vista impact fees, leaving about $456,000 before County fees. A gentle slope adds about 10% of construction; a 100+ ft trench about $20,000.
Bonita rents
| Source | Studio | 1 bedroom | 2 bedrooms |
|---|---|---|---|
| Zillow, Bonita (Nov 5, 2026, 26 listings) | n/a | $2,195 | $2,812 |
| Zumper, Bonita (Oct 1, 2026) | $1,797 | $1,925 | $2,795 |
| HUD FY2027 FMR (metro-wide) | not set here | $2,335 | $2,823 |
Thin samples: Bonita averages swing month to month, and Zillow's $3,000 studio figure is too sparse to use.
Example: a 740 sq ft one-bedroom at about $327,000 renting for $2,195 grosses $26,340. After 5% vacancy ($1,317), 6% upkeep ($1,580) and roughly $1,220 of new property tax, about $22,200 remains before insurance, near a 15-year payback, or about 16 with a $25,000 leach field.
Sunnyside, Lincoln Acres and other County pockets
Sunnyside lives on in the fire district's name and Sunnyside Elementary, but we found no map of its edges, so trust the parcel report. Lincoln Acres, about 2,100 people with a 91950 ZIP, is County land ringed by National City; PDS permits it, while the National City ADU page covers the city around it. The Eastlake and Otay Ranch ADU guide covers the master-planned City neighborhoods east of Bonita, and the Chula Vista areas hub lists the rest.
In pictures
Pieces of a backyard unit on a larger lot
These are licensed stock photos (Pexels) chosen to show the kind of space or place described. They are not photographs of our contractor's completed projects.
Bonita ADU questions
Bonita is in the County. Are the ADU rules different from Chula Vista?
Yes. County PDS issues the permit, a detached unit gets 1,200 sq ft whatever the house size, the County bulletin lists 24 ft of height, and since September 2026 an ADU can be sold as a condo. Annexed Bonita-Sunnyside parcels follow the City.
Are the County ADU plans free?
They were billed as free in 2019 and still download from the County site, but no price is listed now. At about 85% complete, they still need a site plan, energy work, trusses and any septic layout.
Can my ADU share my septic system?
Seldom without work. DEHQ says a second dwelling almost always outgrows the existing tank and field, though an amply sized tank can occasionally serve both. A septic professional picks between enlarging and adding a system, and DEHQ approves that layout before the building permit.
Must the owner live on a Bonita property with an ADU?
No owner rule applies to an ADU. For a JADU, the County code still requires it, but since January 2026 state law limits that to a JADU with a shared bath, and HCD asked the County to align. Ask PDS what it enforces.
Sources
- County of San Diego PDS, Accessory Dwelling Units (size limits, fee waiver dates, separate-sale program, contacts)
- County of San Diego, Ordinance 11016 amending Section 6156 (adopted August 19, 2026, effective September 18, 2026)
- County of San Diego, Dwelling Unit Building Plans and KPBS on the 2019 launch
- California HCD, ADU ordinance findings letter to the County of San Diego (July 7, 2026)
- County DEHQ, ADU and second dwelling FAQ for septic properties (rev. February 1, 2021)
- County of San Diego, Property Summary Report
- Chula Vista Municipal Code Chapter 19.72, Zoning regulations for Bonita-Sunnyside
- County of San Diego, Sweetwater Community Planning Area
- Bonita-Sunnyside Fire Protection District, agency profile
- Sweetwater Authority application guide (service area) and Otay Water District, About
- San Diego County Water Authority, capacity charges (2026 and 2027)
- Chula Vista Elementary School District developer fees and Sweetwater Union High School District developer fees
- Better Place Design & Build, County ADU requirements (builder summary of fees, height and setbacks)
- SnapADU, septic systems for ADUs (builder estimates, February 2026)
- Bonita, California and Lincoln Acres, California
- Zillow, Bonita rental market, Zumper, Bonita and HUD FMR datasets
Last checked November 7, 2026. Still open: the current County detached height, County permit and impact fee amounts, whether County plans are free, the conditions in Ordinance 11016, whether the County changed Section 6156 after HCD's July 2026 letter, which ADU standards Chula Vista applies to Chapter 19.72 parcels, Sweetwater and Otay meter fees, and which Bonita streets are on septic. Check each with PDS, Environmental Health, your water district and the fire district.
Next step
Get your free Chula Vista ADU Fit Check
Three short steps, about a minute. A licensed San Diego County general contractor reviews what you send, checks your lot against the City's ADU rules, your HOA and your water district, and replies with a realistic range and the questions that would change it.
- Which ADU types your lot allows, and the size and height limits that apply
- Whether your HOA, a CFD or your water district changes the plan
- A line-by-line range, including fees and utility runs, before you pay for drawings
- No obligation and no pressure follow-up