An ADU is a secondary housing unit on a residential lot, with its own kitchen, bathroom, and entrance. From 2015 to 2023, Walnut Creek issued 147 ADU building permits, representing about seven percent of the city’s new housing.

Keep reading to learn the key requirements—and how Samara can help you build one.

In accordance with California state law, the City of Walnut Creek will review your ADU application within 60 days of submission. While approval timelines vary, most projects take about three to four months from application to permit.

Here’s what to know before planning and designing an ADU in Walnut Creek:

The maximum size of an ADU in Walnut Creek depends on the number of bedrooms and, in some cases, the size of the lot.

Here’s a breakdown:

All ADUs in Walnut Creek must have minimum side and rear setbacks of four feet. Converted structures may be allowed to maintain their existing footprint, even if closer than four feet to the property line.

ADUs in Walnut Creek must match the architecture of the primary residence—unless they qualify as exempt under state law (often referred to as “66323 Units”). ADUs that are 800 square feet or smaller, under 16 feet in height, and meet minimum setbacks are generally exempt from local design standards.

For all other ADUs, the following design elements must match the main home:

If the main home uses a mix of materials, the ADU should reflect the materials that make up the majority of the primary structure. Unusual shapes (such as circular or triangular floor plans) are not permitted unless they mirror the design of the main home.

The City of Walnut Creek does not require new parking spaces for ADUs or JADUs. If you convert an existing garage, carport, or other parking area into an ADU, you are not required to replace the lost parking.

ADUs in Walnut Creek are permitted on any property with an existing or proposed residential use. This includes all single-family and multi-family residential zones, mixed-use districts, and zones that permit religious assembly use.

JADUs are allowed on lots with a single-family home, including those in single-family zoning districts and multi-family zones where single-family dwellings are permitted.

Single-family properties in Walnut Creek may include one ADU—either detached, attached, or a conversion—and one Junior ADU (JADU), as long as a primary residence exists or is under construction. In some cases, both a new detached ADU and a conversion ADU may be allowed on the same lot, provided one is under 800 square feet.

Multi-family properties with an existing residential building may add up to eight detached ADUs, not exceeding the number of existing units. Interior spaces such as storage rooms or offices can also be converted into ADUs, up to 25 percent of the existing unit count, with a minimum of one allowed.

If you’re looking to build an ADU, Samara makes it easy. We handle everything from permits to installation and even offer our own financing. Call us at 650-420-2607 to schedule a 15-minute consultation and discover how simple adding a Backyard ADU can be.

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