Two Detached ADUs in Walnut Creek (AB 956, 2027)
Plan Two ADUs in Walnut Creek: Free Site Assessment
Walnut Creek ADU rules today (2026)
From January 1, 2027, state law (AB 956) requires the City of Walnut Creek to approve up to two detached ADUs on a lot with a single-family home. Walnut Creek already requires no parking for ADUs and decides applications within 60 days, which helps a two-unit project move quickly.
- Code: Zoning Code §§ 10-2.3.501 to .507, amended by Ordinance No. 2246 (October 15, 2024) and Ordinance No. 2250 (August 5, 2025).
- Units allowed now: the city’s ADU code allows one attached or converted ADU, one detached new-construction ADU and one JADU on a single-family lot. A detached ADU over 800 sq ft is allowed only if it comes before any other ADU on the lot.
- Size by lot: under 15,000 sq ft, 850 sq ft (studio or one bedroom) or 1,000 sq ft (two or more); up to 950 sq ft (studio or one bedroom) on lots of 20,000 sq ft and up. JADUs are 500 sq ft.
- Height: 16 ft for a detached ADU, 18 ft near major transit. Attached: 25 ft and two stories.
- Setbacks: 4 ft maximum side and rear. Front setback and lot coverage limits are waived as needed for an 800 sq ft ADU.
- Parking: none required for ADUs or JADUs.
- Process: ministerial, decided within 60 days of a complete application or deemed approved.
- Programs: Pre-Reviewed ADU Plans (PRADU), ADU amnesty and an ADU rebate program.
State review of Walnut Creek's ADU rules
HCD reviewed Walnut Creek twice. Its May 23, 2023 letter raised the unit allowance and 16 ft heights. Its August 25, 2025 letter on Ordinance No. 2246 raised the timing rule for detached ADUs over 800 sq ft and the pre-reviewed plan program. The city replied on September 18, 2025 and committed to further amendments. Where local rules are stricter than state law, state law applies.
Recent Axiom work
Professional photos from a recent Axiom Renovation full remodel and addition in Los Gatos.
What changes on January 1, 2027
AB 956 raises the number of detached, new-construction ADUs the city must approve from one to two. The city may cap each at 800 sq ft of living space and apply height limits; side and rear setbacks can be no more than 4 ft. Where two are built, the city need not approve a JADU. HOA protections also apply.
Walnut Creek allows one detached new-construction ADU today, and a detached unit over 800 sq ft only if it comes first. Under AB 956, two detached units of up to 800 sq ft each line up with the city’s existing 800 sq ft track. The city will need to update its ordinance, and we confirm the current rules as it adopts changes.
Planning two detached ADUs on a Walnut Creek lot
- Hillside lots: on lots averaging 15% slope or more outside the Core Area and Rossmoor, the city’s ADU code bars building on true slopes over 30% or near highly protected trees, and sets a 100 ft ridgeline setback and 50 ft from faults and creek banks.
- Trees: certain ADUs and JADUs are exempt from the city’s tree ordinance; we confirm whether yours is before design.
- Fire: sprinklers are not required if the main house is not sprinklered. Detached units must meet Fire Code access distances, which matters for a second unit deeper on the lot.
- Utilities: Central San serves Walnut Creek for sewer. Two units usually need a load calculation and often an electrical service upgrade, plus sign-off from your water provider.
Building ADUs in Walnut Creek with Axiom
Axiom Renovation designs, permits and builds ADUs. For two units we start with a site study of fit, utilities and review path. See our Walnut Creek ADU builder page, our Walnut Creek service area page, the AB 956 overview, and guides for nearby Lafayette and Alamo.
Process
Our ADU Process
Step 1
Initial Consultation
We begin with a thorough initial consultation to understand your needs, assess your space, and discuss your vision, budget, and timeline.
Step 2
Planning and Design
At Axiom Renovation, we understand that the planning and design phase of an ADU project is crucial to its success. Our dedicated project managers will work closely with you to understand your goals, design ideas and budget for the project.
Step 3
Material Selection
We guide you through selecting high-quality materials that fit your design and budget, ensuring durability and aesthetic appeal.
Step 4
Demolition and Preparation
Careful demolition and preparation work are performed to ready the space for construction, minimizing disruptions and ensuring a clean work environment.
Step 5
Construction and Installation
Our skilled craftsmen handle the construction phase, including obtaining permits, scheduling appointments, and the actual construction and installation with precision, building the new space according to the approved design.
Step 6
Electrical and Plumbing Work
Licensed professionals conduct all electrical and plumbing work, ensuring everything is up to code and seamlessly integrated into the new ADU.
Step 7
Painting and Finishing
We pay close attention to detail during the painting and finishing stage, ensuring all surfaces are properly prepared and beautifully finished.
Step 8
Fixture and Appliance Installation
We expertly install all fixtures and appliances, ensuring they function correctly and fit perfectly with the overall design.
Step 9
Final Touches and Clean-Up
Final touches are added, and a thorough clean-up is performed, leaving your new space pristine and ready for use.
Step 10
Final Walkthrough and Client Satisfaction
We conduct a final walkthrough with you to ensure every detail meets your expectations and address any remaining concerns, ensuring your complete satisfaction.
Walnut Creek Two-ADU FAQ
Can I build two detached ADUs in Walnut Creek?
From January 1, 2027, AB 956 requires the city to approve up to two detached, new-construction ADUs on a lot with a single-family home, if the project meets objective standards. Today the city allows one detached ADU plus an attached or converted ADU and a JADU.
How large can each ADU be in Walnut Creek?
Today the cap depends on lot size, from 850 to 950 sq ft for a studio or one bedroom and 1,000 sq ft for two or more. Under AB 956, the city may limit each of two detached ADUs to 800 sq ft of living space.
Do I need parking for an ADU in Walnut Creek?
No. Walnut Creek does not require parking for ADUs or JADUs.
How long does Walnut Creek take to approve an ADU?
The city must decide within 60 days of a complete application, or the ADU is deemed approved. Review is ministerial.
Can I build an ADU on a hillside lot in Walnut Creek?
Often, yes, with limits. On lots averaging 15% slope or more, no construction is allowed on slopes over 30%, and ridgeline, fault and creek setbacks apply.
Who builds two-ADU projects in Walnut Creek?
Axiom Renovation designs, permits and builds ADUs in Walnut Creek and is planning two-unit projects for 2027. Call 408-702-2022, Monday to Friday, 9 am to 5 pm.
Sources: AB 956 (Quirk-Silva), signed September 29, 2026, effective January 1, 2027, as summarized by Brownstein Hyatt Farber Schreck and California YIMBY. This page is general information, not legal advice. Local rules change; we confirm current requirements with the city for every project.