ADU Builder in Walnut Creek, CA
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In Walnut Creek, Lot Size Sets ADU Size
Walnut Creek’s ADU ordinance (Municipal Code ยง10-2.3.501 and following, updated in 2024 and 2025) scales the maximum ADU size to your lot. Under the current code text:
| Net lot area | Studio or 1 bedroom | 2+ bedrooms |
|---|---|---|
| Up to 14,999 sq ft | 850 sq ft | 1,000 sq ft |
| 15,000 to 19,999 sq ft | 900 sq ft | 1,000 sq ft |
| 20,000 sq ft or more | 950 sq ft | 1,000 sq ft |
A single-family lot can have one attached or conversion ADU, one detached ADU and one junior ADU (up to 500 sq ft). An attached ADU over 800 sq ft cannot exceed 50% of the main house. No parking is required. The City has committed to further ordinance updates after state review in 2025, so we confirm the numbers for your lot before design.
ADU Construction
Walnut Creek ADU Design Standards
- Siding, trim, building shape, roof form, pitch and material must match the main house.
- Windows must match at least two of five listed features of the main house.
- Each ADU needs its own exterior entrance.
- Second-story windows within 10 feet of a side or rear lot line need a sill at least 5 feet above the floor.
- Detached ADUs: 16 feet tall, or 18 feet near major transit plus 2 feet to match the roof pitch. Attached ADUs: up to 25 feet, two stories.
- Side and rear setbacks of no more than 4 feet are required.
- On slopes of 15% or more outside the Core Area and Rossmoor, hillside rules apply.
ADUs are exempt from Walnut Creek design review and are approved ministerially within 60 days of a complete application.
Pre-Approved ADU Plans
Walnut Creek offers two shortcuts: City-developed Pre-Reviewed ADU (PRADU) plans, and a third-party program in which a designer’s pre-approved plans skip standard plan check. A site plan is still reviewed for your lot. We can build from a pre-approved plan or a custom design.
Walnut Creek issues its own permits. Unlike Lafayette, Orinda or Moraga, Walnut Creek has its own Building Division that reviews plans, issues building permits and inspects the work. Plan check is electronic. The City’s published maximum for a first review of new residential work is 23 business days, with 18 for rechecks, and its goal is to approve most residential alterations and ADUs within two review rounds.
City Hall, 1666 North Main Street, 2nd Floor, Walnut Creek, CA 94596
Building permit technicians (925) 943-5834 · Duty planner (925) 256-3558 · Inspections (925) 943-5833
In person Monday to Thursday by appointment, with walk-ins taken as available; Fridays are remote service. All permit applications are filed through the City’s online Accela portal; paper and emailed applications are not accepted.
Inspections are scheduled through Accela or by phone before midnight for next-day service. Construction on Saturdays and City holidays needs an after-hours permit.
Walnut Creek ADU FAQ
How big can an ADU be in Walnut Creek?
It depends on lot size: 850 to 950 sq ft for a studio or one bedroom and 1,000 sq ft for two or more bedrooms, under the current code text. A junior ADU is up to 500 sq ft.
Do I need parking for an ADU in Walnut Creek?
No. Walnut Creek does not require parking for ADUs or JADUs.
Does Walnut Creek have pre-approved ADU plans?
Yes, City Pre-Reviewed ADU plans and a third-party pre-approved plan program.
Who issues ADU permits?
The City of Walnut Creek Building Division, through its online Accela portal.