Walnut Creek, CA Accessory Structures: ADU Rules (2026)

California's state ADU laws preempt local restrictions. Walnut Creek's ADU Ordinance implements Gov Code 65852.2: (1) One ADU and one JADU are allowed by right on any single-family lot. (2) Detached ADUs up to 800 sq ft with 16-ft height cannot be denied based on local standards, with required side/rear setbacks of just 4 ft. (3) Lots within a half-mile walking distance of major transit (Walnut Creek BART, Pleasant Hill/Contra Costa Centre BART, or high-frequency bus) cannot be required to provide replacement parking when converting a garage to an ADU or adding an ADU. (4) Impact fees are prohibited for ADUs under 750 sq ft. (5) The city must approve or deny a complete ADU application within 60 days. (6) Under AB 1033 (2024), cities must permit ADU condoization if they opt in. JADUs (max 500 sq ft) must be within the primary dwelling's existing footprint, can share a bathroom, and require owner-occupancy of either the primary or JADU unit. Permits are obtained from Walnut Creek's Community Development Department; typical fees run several thousand dollars for plan check and building permit. HOAs cannot unreasonably restrict ADUs (Civil Code 4751). Short-term rental of ADUs is generally prohibited under state law — minimum 30-day rentals.