San Bernardino County ADU Requirements: Size, Setbacks, and Permits

San Bernardino County ADU requirements let any homeowner on a residentially zoned parcel build at least one accessory dwelling unit, with the county layering its own development standards on top of California’s state ADU floor. The rules are set out in County Development Code Section 84.01.050 and Chapter 84.36, and they govern how many units you can have, how big they can be, how far from the property line they must sit, and what you need to submit to get a permit.¹ Below is what each of those pieces actually requires.

How Many ADUs Your Parcel Can Hold

The county counts ADUs, junior ADUs (JADUs), and guest houses together toward a single cap that depends on your lot size.

Parcels under 5 acres: up to two accessory units in any combination of ADU, JADU, or guest house.
Parcels 5 acres or larger: up to three accessory units in any combination.
Only one JADU is allowed per parcel, but it can coexist with a full ADU.
On multifamily properties, attached ADUs can be created within unused portions of existing buildings — at least one, up to 25 percent of the existing unit count. Two detached ADUs are also allowed on multifamily lots.

Owners of larger rural parcels in the desert and mountain regions get meaningfully more capacity than owners of standard suburban lots. Confirm your parcel’s zoning designation with Land Use Services before you spend money on design.¹

The Four Configurations

Attached ADUs share at least one wall with the primary residence. Detached ADUs stand alone on the same lot. Conversion ADUs repurpose existing space such as a garage, basement, or other accessory structure. A junior ADU is a distinct category: no more than 500 square feet, contained entirely within a single-family residence, with an efficiency kitchen and a separate exterior entrance.²³ A JADU can share a bathroom with the main house or have its own, and that choice now drives the owner-occupancy rule described below.

Size, Height, and Setbacks

Size Limits

Studio or one-bedroom ADU: up to 850 square feet.
Two or more bedrooms: up to 1,000 square feet.
Detached ADU: up to 1,200 square feet, but if the unit would push the property past its lot coverage limit, the maximum drops to 800 square feet.
JADU: 500 square feet maximum, entirely within the single-family home.

The 800-square-foot fallback is state-mandated. Even on a tightly built lot, the county cannot deny a detached ADU with 4-foot setbacks that stays at or below 800 square feet.⁴

Height

Under the county’s 2026 standards, attached ADUs can reach 25 feet and detached ADUs can reach 18 feet. An extra 2 feet is allowed if the ADU’s roof pitch matches the primary dwelling. No ADU can exceed two stories regardless of the height allowance.² Conversions of existing structures keep whatever height the original structure had.

Setbacks

Side and rear yard setbacks for both attached and detached ADUs are capped at 4 feet. The county cannot require more.² Conversions of existing structures require no setback at all, and the same zero-setback rule covers a new structure built in the same location and to the same dimensions as one being replaced.⁵ Front yard setbacks follow the underlying zoning district, but they cannot prevent an ADU of at least 800 square feet from being built, even if it would sit partially or wholly within the front setback area.

Parking

The baseline rule is one parking space per ADU, but most projects qualify for an exemption. No parking can be required when any of the following apply:

The ADU is within a half-mile walking distance of public transit with fixed-route service.
The ADU is within an architecturally and historically significant historic district.
The ADU is part of the existing primary residence or an accessory structure, which covers all conversions and attached units.
On-street parking permits are required in the area but not offered to the ADU occupant.
A car-share vehicle is located within one block of the ADU.

When a garage, carport, or covered parking structure is demolished or converted to build an ADU, the county cannot require the lost parking spaces to be replaced.⁵ That matters because garage conversions are one of the most common ADU strategies.⁴

Owner-Occupancy, Rentals, and Separate Sale

California law prohibits local agencies from imposing any owner-occupancy requirement on a full ADU. You do not need to live on the property to build or rent one out.⁵

JADUs work differently. If the JADU shares a bathroom with the primary residence, the owner must live in either the main house or the JADU. If the JADU has its own bathroom, owner-occupancy is not required. AB 1154 made that distinction effective January 1, 2026.⁵ Every JADU also requires a recorded deed restriction prohibiting separate sale from the primary residence.³

San Bernardino County allows both short-term and long-term ADU rentals. Short-term rentals in the Mountain or Desert Region require a separate Short-Term Rental Permit with its own eligibility rules, so confirm with Land Use Services before listing on a platform like Airbnb.⁴

One boundary worth stating: an ADU generally cannot be sold separately from the primary residence. AB 1033 lets California cities and counties opt in to allow separate condominium-style sales, but each jurisdiction must adopt its own ordinance. Absent that opt-in, your ADU stays tied to the primary property deed.

Fire Sprinklers and Energy Code

Fire sprinklers follow a simple rule: if the primary dwelling already has them, the ADU must too. Building an ADU does not trigger a requirement to retrofit sprinklers into the existing main house. All newly constructed dwellings require automatic residential sprinkler systems under current California building code.⁶ New ADUs must also meet fire department access and water supply standards.

Every ADU must comply with California’s energy efficiency standards under Title 24, Part 6, covering insulation, mechanical systems, and envelope performance. Your submittal has to include energy compliance documentation. Factory-built and site-built ADUs face the same Title 24 requirements.⁷

The Permit Application

Applications go through the county’s EZ Online Permitting portal (EZOP), or in person at a Land Use Services office.⁸ A complete package typically includes:

A site plan showing all existing structures and the proposed ADU, with dimensions, setbacks, and lot coverage calculations.
Floor plans with exact room dimensions.
Elevation drawings showing height and exterior design.
Title 24 energy calculations.
A building permit application with owner information, licensed contractor details, and scope of work.

Forms are posted on the Land Use Services website.⁹

Review Timelines

State law gives the county 15 business days to determine whether your application is complete. If you hear nothing in that window, the application is automatically deemed complete under SB 543, effective January 1, 2026. From completeness, the county has 60 days to approve or deny. Pre-approved standard ADU plans, where available, get a shorter 30-day review limited to site-specific conditions. If plan check turns up issues, you’ll receive a correction list and can upload revised drawings through EZOP. Permit fees come due before the final building permit issues, and the amount depends on project valuation and square footage.

Impact Fees and Utility Connections

ADUs under 750 square feet are exempt from all impact fees. For ADUs of 750 square feet or larger, impact fees must be proportional to the size of the primary dwelling. The county cannot charge the same flat fee it would charge for a new single-family home.

Utility connections for water, sewer, or septic have to be verified during planning. A detached ADU often needs its own connections and may trigger capacity charges from the local water district. Conversion ADUs that stay within the existing footprint usually tap into the primary home’s infrastructure and avoid new connection fees. Fees vary significantly by service provider, so contact your water district early for exact numbers.

Legalizing an Unpermitted ADU

If your property has an ADU built without permits before January 1, 2020, AB 2533 (effective January 1, 2025) created a pathway to legalize it. The county cannot penalize you for having the unpermitted unit when you apply. An inspector can evaluate the unit against health and safety standards and provide recommendations, but the county cannot deny the permit for code violations unless correcting the violation is necessary to address conditions that would make the building substandard.¹⁰

The county also cannot require you to retroactively pay impact fees or connection and capacity charges for these pre-2020 units. Those fees can run into thousands of dollars on new construction, so the compliance window is considerably more forgiving than what existed before 2025.

1
San Bernardino County Code of Ordinances. San Bernardino County Code 84.01.050 – Residential Accessory Structures and Uses
2
San Bernardino County. Accessory Dwelling Unit Information
3
California Legislative Information. California Government Code 65852.22
4
San Bernardino County Land Use Services. Accessory Dwelling Unit Handout
5
California Department of Housing and Community Development. Accessory Dwelling Unit Handbook March 2026
6
California Department of Housing and Community Development. IB 25-004 Accessory Dwelling Unit
7
California Energy Commission. 2025 Energy Code Accessory Dwelling Units FAQs
8
San Bernardino County. EZ Online Permitting
9
San Bernardino County Land Use Services. Forms and Applications
10
Digital Democracy. AB 2533 – Junior Accessory Dwelling Units