A guide for building backyard homes in

Walnut Creek, California

In Walnut Creek, you can build an Accessory Dwelling Unit (ADU) on your property if it is zoned for single-family or multiple-family dwellings.

Yes, you need a permit to build an Accessory Dwelling Unit (ADU) in Walnut Creek. The Walnut Creek Municipal Code outlines specific requirements and standards for ADUs in different zoning districts, indicating that both the construction of new ADUs and the conversion of existing structures into ADUs are subject to regulatory approval. This includes attached ADUs within the gross floor area of existing or proposed single-family dwellings, detached ADUs within existing accessory structures, and new detached ADUs subject to size, height, and setback requirements​​

The average time the city of Walnut Creek takes for your permit application is 60 days of submission. It is possible to get your permit approved within 30-90 days of submission so long as your designs are drawn with the local code in mind.

At Type Five, we take care of your entire permit process. Our ADU plans meet the highest standards of construction and building code across California, ensuring that our permits are approved in the shortest time possible.

The number of ADUs you can have in Walnut Creek depends on whether or not your lot has a single-family dwelling (and the amount of single-family dwellings on the lot) or has a duplex or multiple-family dwelling on the lot.If you have a lot with one single family dwelling you are allowed 1 ADU and 1 JADU.

If you have a lot with more than one single family dwelling you are allowed 1 ADU and no JADUs.

If you have a lot with a multi-family residence, you are allowed to have up to 2 ADUs.

There is no minimum lot size requirement for an ADU in Walnut Creek. California state law also mentions that lot coverage requirements can’t preclude the creation of a statewide exemption ADU. A statewide exemption ADU is 800 square feet, with a height limitation of 16 feet and and 4 feet rear and side yard setbacks.

With Type Five, you can design an ADU to fit whatever available space you have in your backyard. Our system can flex and adapt to ensure you can build high-quality livable space even if it's in a smaller area. Get started with designing your ADU here.

There is no minimum size for building an ADU in Walnut Creek. California state law gives local governments the ability to set minimum and maximum height standards. However they cannot require a minimum square footage requirement that prohibits an efficiency unit.

Type Five's ADUs can adapt to a variety of different sizes for your needs. Get started with designing yours here.

For a one-bedroom or studio ADU, the maximum size for building an ADU in Walnut Creek is 850 square feet; however, if your lot is larger than 15,000 square feet, the maximum can extend up to 950 square feet. For a two-bedroom ADU, the maximum size is 1,000 square feet.

In Walnut Creek, the height limit for an Accessory Dwelling Unit (ADU) is generally set at a maximum of 16 feet for detached ADUs. This makes it challenging to incorporate a two story ADU that have a minimum of 7ft of interior ceiling height.

There is no limit to the number of bedrooms an ADU can have in the city of Walnut Creek according to California state law. The California HCD ADU handbook states that a limit on the number of bedrooms could be construed as a discriminatory practice towards protected classes, such as familial status, and would be considered a constraint on the development of ADUs.

All ADUs built in Walnut Creek and the state of California are required to have 4-foot side and rear yard setbacks. State law allows a local government to determine its own front yard setback requirements. Walnut Creek requires a 20-foot front yard setback.

In the city of Walnut Creek, an ADU is generally not required to have its own electrical panel, water meter, or gas meter unless the ADU was built at the same time as a new single-family dwelling on the property. However, owners of ADUs that plan to be used as rental units typically install a new set of utility meters to make billing cleaner for tenants.

You are not required to install fire sprinklers in an ADU in Walnut Creek so long as sprinklers are not required in your main residence.

You are generally exempt from installing solar panels on your ADU if your ADU is less than 750 square feet.

You should be able to rent an ADU in Walnut Creek for $2,577, which is the average monthly rent for a one-bedroom apartment so long as the rental term is longer than 30 days.

You cannot use an ADU as an AirBnB in Walnut Creek unless you are renting it out for a period longer than 30 days. California law states that ADUs created under subdivision (e) of Gov. Code, § 65852.2 cannot be rented for a period less than 30 days. This means you cannot use your ADU as a short-term rental in Walnut Creek.

Your local homeowners association (HOA) cannot prohibit the construction of an ADU or JADU in Walnut Creek. Assembly Bill 670 (2019) and AB 3182 (2020) amended Section 4751, 4740, and 4741 of the Civil Code to preclude common interest developments from prohibiting or unreasonably restricting the construction or use, including the renting or leasing of, an ADU on a lot zoned for single-family residential use.

Covenants, conditions and restrictions (CC&Rs) that either effectively prohibit or unreasonably restrict the construction or use of an ADU or JADU on such lots are void and unenforceable or may be liable for actual damages and payment of a civil penalty.

The city of Walnut Creek will assess the value of your newly added ADU, typically by using the cost-based method of appraisal, and multiply it by the property tax rate of 1.3%. So, if your ADU in Walnut Creek costs $200,000 to build, you can expect your annual property taxes to increase by $1,300 per year. Adding an ADU to your property will not trigger a reassessment of the value of your primary residence.

Adding an ADU to your property in Walnut Creek typically adds value to your property, however, the exact amount depends on the appraisal method that your appraiser chooses to use. If an appraiser uses the cost-basis method & the cost of your ADU is $200,000, then you can expect your home value to appreciate by $200,000.

Another method that an appraiser can use is the sales comparison approach, where the value of the ADU addition is determined by recently sold properties in Walnut Creek that included ADUs. However, this approach depends on the number of recently sold properties and there sometimes isn’t enough information to use this approach with ADUs. A back-of-the-envelope way to estimate the value yourself would be to multiply the existing price per square foot of your property by the square footage added by the ADU and compare it to the cost of your ADU. The appreciation is likely in between those two numbers.

The average cost to build an ADU in Walnut Creek is $230,000. Keep in mind there are a ton of factors to consider when estimating the cost of a project, many of which are unique to your property and sometimes require special surveys to identify. Examples of these factors include whether or not your property is flat or sloped and whether or not you need to upgrade your utilities.

It’s also important to note that converting an existing structure or converting your garage into an ADU isn’t necessarily cheaper than building a brand new detached ADU. You can get an in-depth overview about what goes into the costs of building an ADU in your city on our cost calculator page, or you can get a brief idea of what costs look like below.