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All ADU Regulations

Walnut Creek, California

Walnut Creek has an interim ADU ordinance in place to comply with new state laws. Read all the up-to-date requirements to permit an ADU in Walnut Creek.
Updated Dec 18, 2019


Your eligibility to build an ADU depends on your zoning district. All of the below districts are eligible to build ADUs. Check the zoning of your property here:
  • Single family residential: R-8, R-8.5, R-10, R-12, R-15, R-20, R-40
  • Duplex & multifamily: D-3, M-0.75, M-1, M-2, M-2.5, M-3
  • Other: M-H-D, H-P-D, M-U, O-S-R, HO P-D, P-D, SFH-PD1, MU-C, MU-R, MU-D

Number of units

The number of ADUs you’re able to build depends on how your lot is zoned:
  • Lots zoned for single family use may add 1 ADU and 1 Jr. ADU (JADU).
  • Lots zoned for multi-family may add up to 2 ADUs.

Building size

Maximum square footage is determined by your lot size, zoning and ADU type:
  • 500 sq. ft. for a Jr. ADU (JADU)
  • 800 sq. ft. if you have reached the maximum lot coverage and floor area ratio for your lot
  • 850 sq. ft. for a 1 bedroom ADU on lots <15,000 sq. ft.
  • 900 sq. ft. for a 1 bedroom ADU on lots 15,000-19,999 sq. ft.
  • 950 sq. ft. for a 1 bedroom ADU on lots >20,000+
  • 1,000 sq. ft. for 2+ bedroom ADU
  • An attached ADU may reach 800 sq. ft. or 50% of the existing living area, whichever is more

Building height

Detached ADUs can reach a maximum height of 16 feet. Attached ADUs can reach the same height as the main structure, assuming they comply with municipal code (including daylight plane).


Minimum setbacks of 4 feet from the side and rear lot lines, as well as 6 feet from any existing structures are required for detached ADUs. No setback is required for an ADU that replaces an existing structure and is located in the same location and to the same dimensions as the structure being replaced.


No additional parking is required for ADUs. Even when converting a garage or carport, replacement parking is not required.


Owner occupancy is not a requirement for permitting an ADU from January 1, 2020 until January 1, 2025. This is a great opportunity for rental property owners to increase their yields in a cost-effective way.


While long-term rentals are permitted for ADUs, homeowners may be required to sign a deed restriction preventing short-term rentals (e.g. Airbnb for less than 30 days).

Design standards

Walnut Creek requires that the ADU be designed to be architecturally consistent with the main home, including building form, exterior siding and/or trim, roof form and materials, and windows. Any new entrances to an attached ADU should not be street-facing.
When replacing a garage door for a conversion ADUs may require a landscaped area between the former garage door and the driveway.


Lots with an average slope of 15% or greater, or within 50 ft. of a fault line or creek bed may be subject to additional restrictions. Reach out to us and we’ll help you build a custom ADU to fit your unique property characteristics and local regulations!

Want to learn more about ADU regulations in your area?

Book a free consultation and estimate with a Cottage ADU Expert to find out what’s possible on your property!