ADU Rules in San Bernardino County, California
We track 7 cities in San Bernardino County. Each city writes its own ADU ordinance on top of California law, so size limits, fees, and design rules differ from one city to the next. Among the cities we track, San Bernardino has the lowest starting permit fees ($4,000 – $10,000).
Cities
7
Max Detached Size
1,000–1,200 sq ft
Build Costs From
$100,000
Pre-approved Plans
3 of 7 cities
San Bernardino County Cities Compared
| City | Max detached | Height | Permit fees | Build cost |
|---|---|---|---|---|
| San Bernardino | 1,200 sq ft | 16 ft | $4,000 – $10,000 | $100,000 – $220,000 |
| Fontana | 1,200 sq ft | 16 ft | $4,500 – $10,000 | $110,000 – $230,000 |
| Ontario | 1,000 sq ft | 16 ft detached | $4,500 – $10,500 | $115,000 – $240,000 |
| Rancho Cucamonga | 1,200 sq ft | 16 ft (detached), 18 ft within half a mile of major transit | $7,000 – $14,000 | $150,000 – $310,000 |
| Victorville | 1,000 sq ft | 16 ft (detached) | $4,000 – $8,500 | $115,000 – $240,000 |
| Rialto | 1,200 sq ft | 16 ft or one story, whichever is less | $5,000 – $10,500 | $130,000 – $265,000 |
| Hesperia | 1,200 sq ft | 16 ft detached (18 ft within half a mile of major transit) | $4,000 – $8,500 | $115,000 – $235,000 |
San Bernardino ADU rules
San Bernardino allows detached ADUs up to 1,200 sq ft of livable space at 16 ft tall, and offers a Pre-Selected ADU Plans Program where homeowners buy plans directly from design firms. HCD reviewed the city's ADU ordinance in April 2026, so check the city page for any amendments. Many lots are large enough for a full-size detached unit.
Fontana ADU rules
Fontana's city website now lives at fontanaca.gov, where the Planning Department publishes an ADU information sheet and FAQ. Much of the city's housing sits in newer subdivisions with HOAs, so check CC&Rs for design rules even though HOA approval is not a condition of the city permit. Pre-approved detached plans are available through Building & Safety.
Ontario ADU rules
Ontario caps new detached ADUs at 850 sq ft for a studio or one-bedroom and 1,000 sq ft for two or more bedrooms, below the 1,200 sq ft allowed in many nearby cities. Zone lot coverage limits of 30 to 60% can shrink that size, though never below 800 sq ft. The city does not offer its own plans; it points homeowners to private vendors with city-approved plans, but that vendor list was still marked coming soon in 2026.
Rancho Cucamonga ADU rules
Rancho Cucamonga regulates ADUs in its Development Code chapter on ADUs and JADUs, which applies to every lot zoned for single-family or multifamily use with no minimum lot size. Detached ADUs get the state 16 ft height and 4 ft side and rear setbacks, while attached ADUs can reach 25 ft. The city's typical large suburban lots in the Low and Very Low density zones leave plenty of room for a detached unit.
Victorville ADU rules
Victorville is one of the lower-cost places in Southern California to build an ADU, and lots are often large enough for a detached unit. Building submittals can include High Desert items you will not see on the coast, such as a Joshua tree inspection report, grading plans for detached ADUs and a percolation report where septic is involved. Design for wind and summer heat above 105°F.
Rialto ADU rules
Rialto offers a Pre-Selected ADU Plans Program with 11 plans from 499 to 1,200 sq ft (1 to 3 bedrooms), which homeowners license directly from the designer and submit with a site plan. Projects go to Planning first for an address letter, then to Building for plan check. Large Inland Empire lots make detached units the common choice.
Hesperia ADU rules
Hesperia's city website has moved to hesperiaca.gov, where Planning posts its ADU and JADU approval application. Detached ADUs are capped at 1,200 sq ft of livable area, and the planning approval fee is modest. Many High Desert lots rely on septic systems, which adds environmental health review and can lengthen timelines.
Rules that apply in every California city are summarized in our California ADU law guide. See all California cities or compare every city side by side.