California ADU rules · Santa Clara County
Can I Build an ADU in Campbell?
Yes — you can build an ADU in Campbell. California's statewide ADU law requires every city, including Campbell, to approve a qualifying accessory dwelling unit by right, plus a junior ADU (JADU) on a single-family lot. What varies city to city are the local specifics below.
Can you build one?
ADUs allowed
CA state lawYes — by right
ADUs and JADUs are allowed by right in all residential and mixed-use zones; ministerial approval, no hearing.
Units on a single-family lot
CA state law1 ADU + 1 JADU
At least one ADU and one JADU per single-family lot (a conversion ADU may also be possible).
Units on a multifamily lot
Local ruleconversion ADUs: at least 1 or up to 1 per 4 existing units; plus up to 2 detached ADUs per lot
Detached ADUs on multifamily lots capped at 2 per lot, not 8 as in state baseline.
Junior ADU (JADU)
CA state lawAllowed
Up to 500 sq ft, within the walls of an existing single-family home (single-family lots only).
Size & height
Max detached ADU size
Local rule1,200 sq ft
Local maximum matches state cap, but is explicitly codified.
Max attached ADU size
Local rule50% of primary, >=850 (>=1,000 for 2+ bedrooms)
Guaranteed minimum size
CA state law800 sq ft
An 800 sq ft ADU must be allowed regardless of FAR/lot-coverage caps; a city also cannot cap an attached ADU below 850 sq ft (1,000 for 2+ bedrooms).
Max JADU size
CA state law500 sq ft
Max height
CA state law16 ft
16 ft baseline; cities must allow 18 ft within ½ mi of a major transit stop or where the primary dwelling is two-story, and 20 ft on a lot with a multistory multifamily building.
Setbacks
Side setback
CA state law4 ft
A city cannot require more than 4 ft side or rear setback; conversions of existing structures are exempt.
Rear setback
CA state law4 ft
Front setback
Local rulesame as required for the primary dwelling
Separation from main house
Local ruleNone required
10 ft separation if ADU is in front of primary, 5 ft if to the side, none if behind.
Parking
Parking required
Local ruleNone
No parking required for ADUs or JADUs.
Transit parking exemption
CA state lawYes — no parking required near transit & for conversions
No parking may be required within ½ mi walking distance of transit, in a historic district, for an ADU within an existing structure, within one block of car-share, or in certain permit-parking areas.
Garage-conversion replacement parking
Local ruleNot required
No replacement parking required if garage/carport is converted.
Approval, timeline & cost
Approval path
CA state lawMinisterial (by right)
No public hearing or discretionary design review for a qualifying ADU.
Approval timeline
CA state law60 days
The agency must act within 60 days of a complete application — and the ADU is deemed approved if it does not.
Owner-occupancy
Local ruleOnly for a JADU
Owner-occupancy required only for JADUs.
Impact-fee waiver
CA state lawWaived under 750 sq ft
An ADU of 750 sq ft or less pays no impact fees (the 750 sq ft threshold itself is exempt under § 66311.5); larger ADUs pay fees proportional to the primary dwelling. JADUs (≤ 500 sq ft) are exempt.
Permits required
Local ruleBuilding permit, Zoning clearance
Campbell-specific factors that can change the answer
State law sets the floor, but these local conditions often decide whether a specific parcel works.
Historic Properties
Only detached or interior ADUs allowed; must be behind primary dwelling, max 18 ft height, 1 story, and must match primary dwelling design.
Fire Sprinklers
Sprinklers not required for ADUs unless primary dwelling requires them.
Campbell limits detached ADUs on multifamily lots to 2 per lot and requires special placement, height, and design rules for ADUs on historic properties. No parking is required for any ADU or JADU.
Frequently asked questions
Can I build an ADU in Campbell?
Yes. California's statewide ADU law requires Campbell to approve a qualifying accessory dwelling unit ministerial (by right), plus a junior ADU (JADU) on a single-family lot.
How big can an ADU be in Campbell?
A detached ADU of at least 1,200 sq ft must be allowed, and an ADU of 800 sq ft can never be zoned out by floor-area or lot-coverage limits. A JADU can be up to 500 sq ft.
What are the setback requirements for an ADU in Campbell?
Side and rear setbacks are limited to 4 ft. same as required for the primary dwelling.
Is parking required for an ADU in Campbell?
None. No parking can be required within ½ mile of transit, for conversions, or for units inside the primary home. When a garage is converted, replacement parking is not required.
How long does ADU approval take in Campbell?
A complete application must be acted on within 60 days, with ministerial (by right) — no public hearing or discretionary design review for a qualifying ADU.
Do I have to live on the property to build an ADU in Campbell?
Owner-occupancy: only for a jadu. ADUs under 750 sq ft are also exempt from impact fees.
Sources
- Campbell Municipal Code Chapter 21.23 (Ord. No. 2299, § 3, 11-7-2023)
- § 21.23.022, § 21.23.050
- § 21.23.030.G.1
- § 21.23.030.G.2
- § 21.23.030.E, Table 3-1
- § 21.23.030.J.1
- § 21.23.040.G
- § 21.23.080.A
- § 21.23.060
- § 21.23.030.F
- Cal. Gov. Code §§ 66310–66342 (ADU Law)
- HCD 2025 Accessory Dwelling Unit Handbook
- Cal. Gov. Code § 66317 (ministerial approval, 60-day deadline)
- Cal. Gov. Code § 66323 (by-right ADU/JADU, 800 sq ft, 4-ft setbacks)
- Cal. Gov. Code § 66333 (junior ADUs)
- Cal. Gov. Code § 66321 (size minimums & height)
- Cal. Gov. Code § 66322 (ADU parking; § 66334 covers JADU parking)
- Cal. Gov. Code § 66311.5 (impact fees: none for an ADU ≤ 750 sq ft or JADU ≤ 500 sq ft)
Last updated 2026-06-25. This is an AI-assisted summary of Campbell's ADU rules, drawn from its published ordinance and California ADU law — general information, not legal advice, and it may be incomplete or out of date. Verify the controlling rule for your specific parcel with Campbell Planning before relying on it.
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