These rules apply to the UNINCORPORATED areas of San Bernardino County — land outside any incorporated city, regulated by the County Land Use Services Department, not a city planning office. The County's ADU standards follow California state ADU law (Gov. Code §§ 66310-66342). On January 13, 2026, the Board of Supervisors adopted updated ADU regulations that consolidate the County's standards into Development Code Chapter 84.36 and align local rules with recent state law for streamlined, ministerial permitting of ADUs and Junior ADUs. If your property is inside a city (San Bernardino, Fontana, Rancho Cucamonga, Ontario, etc.), that city's rules apply instead.
Zoning & Size Requirements [1][2]
Yes — unincorporated San Bernardino County allows ADUs. A detached ADU can typically be up to 1,200 sq ft under California state law and the County's zoning code.
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| Where ADUs Are Allowed | Parcels with an existing or proposed single-family or multifamily dwelling in residential land-use zoning districts (unincorporated areas) |
| Max Size (Detached) | 1,200 sq ft maximum, 200 sq ft minimum (Table 84-0; minimum measured on livable space and cannot bar an efficiency unit) |
| Max Size (Attached) | 1,200 sq ft maximum and no more than 50% of the existing primary dwelling; 200 sq ft minimum (Table 84-0, note 7) |
| Max Size (JADU) | 500 sq ft maximum, 150 sq ft minimum, contained entirely within the existing single-family residence (Table 84-0, note 6) |
| Max Height | 18 ft detached, plus 2 ft if the ADU roof pitch matches the primary dwelling; 25 ft attached; two storeys maximum (Development Code Table 84-0, notes 10-11) |
| Max Units | 2 ADUs on a single-family lot, or 3 on a lot of five acres or greater, plus 1 JADU — the cap is an aggregate regardless of ADU type. On a lot with existing multifamily: up to 8 detached, not exceeding the existing unit count (Table 84-0, notes 2-3) |
Setback & Parking Requirements [1][2]
Unincorporated San Bernardino County requires a rear setback of about 4 ft for a detached ADU, and one off-street parking space is required. Owner-occupancy is not required — you can rent it out without living on the property.
| Rear Setback | 4 ft; 5 ft separation required between detached units; no setback or height compliance required for a conversion of an existing permitted structure (Table 84-0, note 8) |
| Side Setback | 4 ft (state-law minimum) |
| Front Setback | Must meet the underlying district's front setback |
| Parking Required | 1 space per ADU, except waived near transit, in a historic district, or for conversions/JADUs (per state law) |
| Owner Occupancy | Not required for ADUs (state law removed it; JADUs require the owner to occupy the home or the JADU) |
| Min Lot Size | No zoning minimum — but on a property under half an acre with an existing residence, an Advanced Treatment System sized for each additional dwelling must be approved by Environmental Health Services (Table 84-0, note 13). On septic this is the binding constraint, not the zoning |
Permit Process & Fees [3]
An ADU in unincorporated San Bernardino County is approved administratively — no public hearing — within 60-day ministerial review required by state law once a complete application is submitted; permit fees are Building/plan-check fees scale with size and valuation — confirm current schedule with County Land Use Services.
| Approval Process | Ministerial (no discretionary hearing) building permit through San Bernardino County Land Use Services / Building & Safety |
| Review Timeline | 60-day ministerial review required by state law once a complete application is submitted |
| Permit Fees | Building/plan-check fees scale with size and valuation — confirm current schedule with County Land Use Services |
| Impact Fees | None on an ADU of 750 sq ft or less of interior livable space, or a JADU of 500 sq ft or less (Gov. Code 66311.5(c)(1)); charged proportionately above that. Connection fees and capacity charges are excluded from the exemption |
| Plan Check | Included in permit; timing varies by submittal completeness |
| Pre-Approved Plans | Check County Land Use Services for any pre-reviewed/standard ADU plan options |
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Construction Costs [4]
Building an ADU in unincorporated San Bernardino County typically costs $140,000-$320,000 ($200-$400 per sq ft); a garage conversion runs $70,000-$160,000.
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Construction costs in unincorporated San Bernardino County mirror the surrounding Inland Empire market. Rural parcels can cost more due to septic, well, access, and fire-hazard (WUI) requirements, so treat these as planning ranges and get local bids.
| Average Build Cost | $140,000-$320,000 |
| Cost per Sq Ft | $200-$400 |
| Garage Conversion | $70,000-$160,000 |
| Prefab ADU (Installed) | $100,000-$240,000 |
Finance Your ADU Project
Most ADU projects are funded through HELOCs, construction loans, or cash-out refinancing. Compare rates from top lenders.
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Rental Income Potential [5]
| Avg Rent (1 Bedroom) | $1,500-$2,100/mo |
| Avg Rent (2 Bedroom) | $1,900-$2,700/mo |
| Short-Term Rental | Subject to County short-term rental rules — confirm with Land Use Services |
| Est. Annual ROI | 6-9% annual return |
Recent Law Changes
What's Changed Recently
- San Bernardino County Board of Supervisors adopted an updated ADU ordinance on January 13, 2026, consolidating standards into Development Code Chapter 84.36 and aligning with current state law for streamlined ADU/JADU permitting
- California SB 1211 (in effect): up to 8 detached ADUs allowed on qualifying multifamily lots statewide
- AB 1154 (Jan 2026): JADU owner-occupancy narrowed — a local agency may require it only where the JADU shares a bathroom with the main house (Gov. Code § 66333(b))
- SB 543 (Jan 2026): an ADU application is deemed approved if the agency fails to act within 60 days
Tips for Building an ADU in Unincorporated San Bernardino County
- Confirm first whether your parcel is unincorporated — if it is inside a city's limits, that city's ADU rules apply, not the County's. Check your address with County Land Use Services.
- Unincorporated mountain and desert parcels (e.g., near Big Bear, Lucerne Valley, Phelan) can trigger septic, well, fire-hazard (WUI), and access requirements that add cost and time.
- ADUs 750 sq ft or less of interior livable space skip impact fees — a strong reason to keep a first unit compact.
- Garage and accessory-structure conversions avoid setback requirements when the existing footprint is unchanged.
ADU Builders in San Bernardino County
Looking for an ADU builder in San Bernardino County? ADU projects need a contractor experienced with local zoning, the permit process, and utility connections — not every general contractor has built one. We match San Bernardino County homeowners with experienced local ADU contractors who provide free, no-obligation quotes. Getting at least three bids typically saves 20-40% on the same scope.
Cities Within San Bernardino County
If your property is inside one of these incorporated cities, follow that city's ADU code — not the County rules above:
Sources & References
All data on this page is sourced from official government records and verified market data. View our full methodology.
- San Bernardino County Land Use Services — Planning (ADU) Planning Department — Accessed 2026-06-28
- San Bernardino County — Accessory Dwelling Unit (ADU/JADU) Handout Planning Department — Accessed 2026-06-28
- San Bernardino County Land Use Services — Building & Safety / Permits Planning Department — Accessed 2026-06-28
- Angi — ADU Construction Cost Data Market Data — Accessed 2026-06-28
- HUD Fair Market Rents Government Data — Accessed 2026-06-28
- California ADU Handbook — HCD Government Data — Accessed 2026-06-28
Frequently Asked Questions
What are the ADU rules in unincorporated San Bernardino County?
How much does an ADU permit cost in San Bernardino County?
Do I need owner-occupancy for an ADU in San Bernardino County?
Is my property in unincorporated San Bernardino County or inside a city?
How many ADUs can I build in unincorporated San Bernardino County?
Building in Unincorporated San Bernardino County?
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