Unincorporated only: This page covers the unincorporated area of San Bernardino County — parcels outside any city, regulated by the County Planning / Land Use Services Department. If your address is inside a city (San Bernardino, Rancho Cucamonga, Fontana, Ontario), use that city's ADU page instead.
These rules apply to the UNINCORPORATED areas of San Bernardino County (Bloomington, Muscoy, Mentone, Phelan, Lake Arrowhead, Crestline, Big Bear City, Joshua Tree, Lucerne Valley and similar communities), permitted by County Land Use Services, not a city. ADUs are allowed by right on any lot with an existing or proposed home in the RL, RS, RM, RC, AG, CR and SD-RES zones under Development Code Chapter 84.36 (Ordinance 4504, adopted January 13, 2026). A detached or attached ADU can be up to 1,200 sq ft, 18 ft tall detached (25 ft attached), with 4 ft side and rear setbacks, plus a 500 sq ft JADU inside the house; a single-family lot can hold two ADUs (three on 5 acres or more). The permit is ministerial with a 60-day decision clock, and no impact fees apply to a unit of 750 sq ft or less. If your parcel is inside a city (San Bernardino, Fontana, Rancho Cucamonga, Ontario, Victorville, Hesperia and others), that city's rules apply instead.
Zoning & Size Requirements [1][2][3][4][5][6][7][8]
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.
See what this means for your lot — ask San Bernardino County ADU builders for a quote →
| Where ADUs Are Allowed | Allowed as an accessory use on a lot with an existing or proposed single-family or multifamily dwelling in the RL (Rural Living), RS (Single Residential), RM (Multiple Residential), RC (Resource Conservation), AG (Agriculture), CR (Rural Commercial) and SD-RES zones (Tables 82-4, 82-7, 82-11, 82-17 as amended by Ord. 4504; Chapter 84.36.020). Not allowed in FW, OS, the other commercial zones, or the industrial zones |
| Max Size (Detached) | 1,200 sq ft maximum, 200 sq ft minimum, both measured on livable space; the minimum cannot bar an efficiency unit (Table 84-0, note 5). A conversion of an existing structure has no size cap (Table 84-0). An 800 sq ft unit with 4 ft side and rear setbacks must be allowed regardless of lot coverage (note 1) |
| Max Size (Attached) | 1,200 sq ft maximum and, where there is an existing primary dwelling, no more than 50% of that dwelling's floor area; 200 sq ft minimum (Table 84-0, note 7). State law overrides the 50% rule below 850 sq ft, or 1,000 sq ft for more than one bedroom (Gov. Code 66321(b)(2)) |
| Max Size (JADU) | 500 sq ft maximum, 150 sq ft minimum, contained entirely within the existing or proposed single-family residence (84.36.030(c); Table 84-0, note 6); may share a bathroom with the house, in which case it needs its own exterior entrance plus an interior door to the main living area |
| Max Height | 18 ft for a detached ADU, plus 2 ft if its roof pitch matches the primary dwelling; 25 ft for an attached ADU or a JADU; no ADU may exceed two storeys (Table 84-0, notes 10-11). A conversion keeps the existing structure's height (note 8). By-right units under 84.36.080(b) use the state height floors in Gov. Code 66321(b)(4) |
| Max Units | Two ADUs per single-family lot, or three on a lot of 5 acres or more, counted as one aggregate cap across attached, detached and conversion units, plus one JADU (Table 84-0, notes 2-3). On a lot with an existing multifamily dwelling: conversions of non-livable space up to 25% of the existing units, plus up to 8 detached ADUs not exceeding the existing unit count; a proposed multifamily building gets 2 attached and 2 detached (Table 84-0; 84.36.080(b)(3)-(4)) |
Setback & Parking Requirements [1][2][3][4][5][6][7][8]
Unincorporated San Bernardino County requires a rear setback of about 4 ft for a detached ADU, and parking requirements vary by unit size or location. Owner-occupancy is not required — you can rent it out without living on the property.
| Rear Setback | 4 ft (Table 84-0). A detached ADU must sit 5 ft from other detached structures, or more where the California Building Code or the Fire Safety Overlay (Chapter 82.13) requires it (note 9). No setback or height limit applies to a conversion of an existing permitted structure or its like-for-like rebuild (note 8) |
| Side Setback | 4 ft interior side and 4 ft street side (Table 84-0). An existing multifamily building with under 4 ft side or rear setbacks need not change its footprint to add an ADU (84.36.070(a)(2)) |
| Front Setback | Per the underlying zoning district (Table 84-0). An ADU may be built in front of the primary dwelling if it meets the applicable setbacks (84.36.070(a)(3)) |
| Parking Required | One uncovered space per ADU, tandem on the driveway allowed; none for a JADU (Table 84-0, note 12). Waived within half a mile walking distance of public transit, in a listed historic district, for a unit inside the primary dwelling or a converted accessory structure, where street permits are required but not offered, within one block of car share, or when filed with a new primary dwelling; a garage or carport demolished or converted for an ADU need not be replaced (84.36.080(a)(3)) |
| Owner Occupancy | Not required for an ADU (84.36.060(b); Gov. Code 66315). A JADU requires the owner to live in the house or the JADU unless the JADU has its own bathroom or the owner is a government agency, land trust or housing organization, and a deed restriction barring separate sale must be recorded (84.36.060(b), matching Gov. Code 66333(b) as amended by AB 1154) |
| Min Lot Size | No ADU-specific minimum; lot area, width and depth follow the underlying zone (Table 84-0), and state law bars a minimum that would block an 800 sq ft unit (Gov. Code 66321(b)(3)). The practical limit is sanitation: a lot under half an acre with an existing home needs an Advanced Treatment System approved by Environmental Health Services for each added dwelling (note 13), and a lot within 200 ft of a sewer line (plus 100 ft per unit) must connect to sewer (County ADU handout, March 2026) |
Permit Process & Fees [9][10][11][12][13][14][15]
An ADU in unincorporated San Bernardino County is approved administratively — no public hearing. Typical timeline: Completeness check within 15 business days, then a decision within 60 days of a complete application, or 30 days for a County pre-approved plan (84.36.050(b); Gov. Code 66317, deemed approved if the County misses 60 days). The County publishes no actual average. Permit fees: The FY 2026/27 Construction Fee Schedule (16.0204(a)(1), in effect July 1, 2026) has no ADU line; the nearest row, a Type V R-3 dwelling, is $2,428 combined plan check and inspection up to 1,000 sq ft plus $83.60 per extra 100 sq ft. Run the EZOP Building and Safety Estimator for your parcel.
| Approval Process | Ministerial building permit through County Land Use Services (Building and Safety), no hearing or discretionary review (84.36.050(a)), filed through the EZ Online Permitting (EZOP) portal. Before the permit is issued the County requires written confirmation of sewer service (or Environmental Health approval of the septic system; holding tanks are not allowed), water service (or well approval), fire district sign-off, and site drainage and access approval (84.36.050(f)-(i)). A detached garage being replaced by an ADU gets its demolition permit at the same time (84.36.050(j)). Nonconforming conditions on the lot cannot be made a condition of approval (84.36.050(c)); an unpermitted ADU built before 2020 cannot be refused a permit except for health and safety (84.36.050(d)) |
| Review Timeline | Completeness check within 15 business days, then a decision within 60 days of a complete application, or 30 days for a County pre-approved plan (84.36.050(b); Gov. Code 66317, deemed approved if the County misses 60 days). The County publishes no actual average |
| Permit Fees | The FY 2026/27 Construction Fee Schedule (16.0204(a)(1), in effect July 1, 2026) has no ADU line; the nearest row, a Type V R-3 dwelling, is $2,428 combined plan check and inspection up to 1,000 sq ft plus $83.60 per extra 100 sq ft. Run the EZOP Building and Safety Estimator for your parcel |
| 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; above 750 sq ft they are charged in proportion to the primary dwelling's size (Gov. Code 66311.5(c)(1)). School facility fees are zero at 500 sq ft or less and set by the school district above that (County ADU handout). Utility connection fees and capacity charges are outside the exemption, but a unit converted from existing space owes no separate connection fee or capacity charge unless the lot is on septic and a private well (84.36.080(a)(2)). Fees also differ by utility district and location (March 2026 handout) |
| Plan Check | Combined plan check and inspection fee covers the first submittal and one resubmittal; further corrections cost extra (Building and Safety Permits page). Plans are checked to the 2025 California codes; fire sprinklers are not required if the main house has none (84.36.080(a)(1)). A unit in a floodplain overlay must elevate its lowest floor (84.36.050(k)); a Fire Safety Overlay parcel follows Chapter 82.13 |
| Pre-Approved Plans | Yes: four pre-approved detached plan sets on the Building and Safety Guidance page, drawn to the 2025 California Residential Code: Model B (735 sq ft), Model C (1,008 sq ft), Model D (560 sq ft) and Model H (1,008 sq ft). A pre-approved plan gets a 30-day decision but pays the same permit fees as any ADU of that size (84.36.050(b)(1)). Models D and B sit under the 750 sq ft impact-fee threshold. The March 2026 handout still says three plans |
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Construction Costs [16][17][18]
Building an ADU in unincorporated San Bernardino County typically costs $150,000-$320,000 ($180-$300 per sq ft); a garage conversion runs $75,000-$150,000.
See what this means for your lot — ask San Bernardino County ADU builders for a quote →
Construction costs in unincorporated San Bernardino County track the surrounding metro market. Rural parcels can cost more because of septic, well, access and fire-hazard requirements, so treat these as planning ranges and get local bids.
| Average Build Cost | $150,000-$320,000 |
| Cost per Sq Ft | $180-$300 |
| Garage Conversion | $75,000-$150,000 |
| Prefab ADU (Installed) | $180,000-$320,000 |
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Rental Income Potential [19]
| Avg Rent (1 Bedroom) | $1,500-$1,900/mo |
| Avg Rent (2 Bedroom) | $1,900-$2,300/mo |
| Short-Term Rental | Mountain and Desert Regions only, with a Chapter 84.28 short-term rental permit, and never for a unit built under the state by-right category (84.36.080(b)); Valley Region ADUs and all JADUs: 30+ day terms (84.36.060). |
| Est. Annual ROI | 7-15% gross a year on a $150,000-$320,000 detached build renting at $1,900-$2,300/mo; 12-25% on a $75,000-$150,000 garage conversion at $1,500-$1,900/mo (before taxes, vacancy and financing). |
Recent Law Changes
What's Changed Recently
- Ordinance 4504, adopted by the Board of Supervisors January 13, 2026 and effective 30 days later, moved the County's ADU rules out of Chapter 84.01 into a stand-alone Chapter 84.36 (codified in Supplement S-45): detached height 16 ft to 18 ft (+2 ft roof-pitch match), two ADUs per single-family lot (three on 5+ acres), up to 8 detached ADUs on an existing multifamily lot, 15-business-day completeness check, 30-day decision on pre-approved plans, JADU owner-occupancy dropped where the JADU has its own bathroom
- Building and Safety fees changed July 1, 2026 (FY 2026/27 Construction Fee Schedule 16.0204(a)(1)); the schedule still has no ADU-specific line
- Pre-approved detached ADU plan sets were redrawn to the 2025 California Residential Code (Models B, C, D and H posted May 2026); the County's March 2026 handout counts three, the Building and Safety page lists four
- SB 543 (Jan 1, 2026): a complete ADU application is deemed approved if the County does not act within 60 days (Gov. Code 66317); AB 1154 (Jan 1, 2026): JADU owner-occupancy may be required only where the JADU shares a bathroom with the house (Gov. Code 66333(b)); SB 1211 (2025): up to 8 detached ADUs on an existing multifamily lot, now written into Table 84-0
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 the address in the County's EZOP parcel research tool or call Land Use Services at (909) 387-8311.
- Sanitation decides feasibility on most unincorporated lots: within 200 ft of a sewer line you must connect; otherwise a lot under half an acre needs an Advanced Treatment System approved by Environmental Health for each added unit, and a percolation test no older than 5 years (10 if recertified). Holding tanks are not allowed (84.36.050(f)).
- Mountain and desert parcels (Lake Arrowhead, Crestline, Big Bear City, Wrightwood, Phelan, Joshua Tree, Lucerne Valley) usually sit in the Fire Safety Overlay (Chapter 82.13) and may need well approval, a fire district sign-off and snow-load or WUI construction, all of which add cost and time.
- Keep a first unit at or under 750 sq ft of interior livable space to avoid impact fees entirely; Model D (560 sq ft) and Model B (735 sq ft) of the County's pre-approved plans both qualify and get a 30-day decision.
- Short-term rental of an ADU is legal only in the Mountain and Desert Regions with a Chapter 84.28 permit, and never for a unit permitted under the state by-right category; if Airbnb income is part of the plan, apply under the County's Table 84-0 standards rather than 84.36.080(b) and confirm the region with Planning.
- A garage or accessory-structure conversion needs no setback, height or replacement-parking compliance, has no size cap, and owes no separate utility connection fee unless the lot is on septic and a private well.
- Cost basis: build and conversion ranges are dated Inland Empire industry guides (LA Metro Home Finder June 2026, CaliFirst Remodel May 2026, ADUscale May 2026); rents are anchored on the HUD FY2026 Fair Market Rent for the Riverside-San Bernardino-Ontario metro (1BR $1,777, 2BR $2,201) and the ranges verified for San Bernardino, Fontana, Ontario and Rancho Cucamonga in September 2026; desert and mountain communities rent below the metro figure.
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 Code Title 8 (Development Code) Chapter 84.36 Accessory Dwelling Units, Secs. 84.36.010-84.36.090 and Table 84-0 (Ord. 4504, 2026; Supp. S-45) Municipal Code — Accessed 2026-09-20
- San Bernardino County Development Code Sec. 82.03.040 Table 82-4 (ADU allowed in RC and AG; amended by Ord. 4504) Municipal Code — Accessed 2026-09-20
- San Bernardino County ADU and JADU Ordinance (Ord. 4504) redline: Tables 82-4, 82-7, 82-11, 82-17 and new Chapter 84.36 ordinance — Accessed 2026-09-20
- San Bernardino County Land Use Services Planning Home (Courtesy Public Notice: draft ADU ordinance approved by the Board 01/13/2026, effective after 30 days) Planning Department — Accessed 2026-09-20
- San Bernardino County Accessory Dwelling Unit Information handout (March 2026) Planning Department — Accessed 2026-09-20
- Gov. Code 66321 (size, height and setback floors; SB 543) state_statute — Accessed 2026-09-20
- Gov. Code 66315 (no owner-occupancy requirement for ADUs) state_statute — Accessed 2026-09-20
- Gov. Code 66333 (JADUs; AB 1154 owner-occupancy limit) state_statute — Accessed 2026-09-20
- San Bernardino County Building and Safety: Permits (fees effective July 1, 2026; plan review covers one resubmittal; EZOP estimator) Planning Department — Accessed 2026-09-20
- San Bernardino County Construction Fee Schedule FY 2026/27, Land Use Services 16.0204(a)(1) (R-3 Dwellings, Type V) fee_schedule — Accessed 2026-09-20
- San Bernardino County Building and Safety: Guidance and Technical Handouts (Pre-Approved ADU Plan Models B, C, D, H; IB-0019 ADU 5-year delay in enforcement) Planning Department — Accessed 2026-09-20
- San Bernardino County Pre-Approved ADU Plan Model B (735 sq ft, 2025 CRC); Models C and D and Plan H at the same path Planning Department — Accessed 2026-09-20
- San Bernardino County Accessory Dwelling Unit Handout (July 9, 2024; Chapter 84.01 era, school-fee and transportation-fee tiers) Planning Department — Accessed 2026-09-20
- Gov. Code 66317 (ministerial review, 15-business-day completeness, 60-day deemed approval; SB 543) state_statute — Accessed 2026-09-20
- Gov. Code 66311.5 (impact-fee exemption at 750 sq ft or less; connection fees) state_statute — Accessed 2026-09-20
- ADU Permit Rules: Inland Empire Cities 2026 (June 12, 2026) | LA Metro Home Finder industry — Accessed 2026-09-20
- ADU Costs in California (2026): City-by-City Numbers (May 28, 2026) | CaliFirst Remodel industry — Accessed 2026-09-20
- Prefab ADU in California 2026 - Real Cost & Trade-offs (updated May 2026) | ADUscale industry — Accessed 2026-09-20
- HUD Final FY 2026 Fair Market Rents - Riverside-San Bernardino-Ontario, CA MSA (1BR $1,777, 2BR $2,201) Government Data — Accessed 2026-09-20
- San Bernardino County Land Use Services: EZ Online Permitting fee estimators Planning Department — Accessed 2026-09-20
Frequently Asked Questions
What are the ADU rules in unincorporated San Bernardino County?
In unincorporated San Bernardino County, ADUs are regulated by the County (not a city) and follow California state ADU law. A detached ADU can be up to 1,200 sq ft maximum, 200 sq ft minimum, both measured on livable space; the minimum cannot bar an efficiency unit, attached ADUs up to 1,200 sq ft maximum and, where there is an existing primary dwelling, no more than 50% of that dwelling's floor area; 200 sq ft minimum. Rear setbacks are 4 ft, and qualifying ADU applications are approved administratively, with no public hearing.
How much does an ADU permit cost in San Bernardino County?
In unincorporated San Bernardino County, building and plan-check fees scale with the size and valuation of the ADU, so there is no single flat fee — request the current fee schedule from the County. None on an ADU of 750 sq ft or less of interior livable space or a JADU of 500 sq ft or less; above 750 sq ft they are charged in proportion to the primary dwelling's size (Gov. Code 66311.5(c)(1)). School facility fees are zero at 500 sq ft or less and set by the school district above that (County ADU handout). Utility connection fees and capacity charges are outside the exemption, but a unit converted from existing space owes no separate connection fee or capacity charge unless the lot is on septic and a private well (84.36.080(a)(2)). Fees also differ by utility district and location (March 2026 handout). Total construction typically runs $150,000-$320,000; a garage conversion is cheaper at $75,000-$150,000.
Do I need owner-occupancy for an ADU in San Bernardino County?
Not required for an ADU (84.36.060(b); Gov. Code 66315). A JADU requires the owner to live in the house or the JADU unless the JADU has its own bathroom or the owner is a government agency, land trust or housing organization, and a deed restriction barring separate sale must be recorded (84.36.060(b), matching Gov. Code 66333(b) as amended by AB 1154).
Is my property in unincorporated San Bernardino County or inside a city?
This matters a lot: if your parcel is inside an incorporated city (San Bernardino, Rancho Cucamonga, Fontana, Ontario), that city's ADU code applies instead of the County's. Only unincorporated parcels follow the County rules on this page. Confirm your jurisdiction with the County before designing.
How many ADUs can I build in unincorporated San Bernardino County?
Two ADUs per single-family lot, or three on a lot of 5 acres or more, counted as one aggregate cap across attached, detached and conversion units, plus one JADU (Table 84-0, notes 2-3). On a lot with an existing multifamily dwelling: conversions of non-livable space up to 25% of the existing units, plus up to 8 detached ADUs not exceeding the existing unit count; a proposed multifamily building gets 2 attached and 2 detached (Table 84-0; 84.36.080(b)(3)-(4))
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