A guide to Walnut Creek ADU building regulations in California
Learn about local zoning guidelines, financing options, and getting started with building a custom ADU in Walnut Creek, California.
Introduction to ADUs
A quick overview of what a backyard home offers for you, your family, and your property.
An ADU, or Accessory Dwelling Unit, is a secondary living space on your property that provides complete independence with its own living, sleeping, eating, cooking, and sanitation facilities. ADUs are also known as guest houses, in law suites, in law units, backyard cottages, and granny flats, and are built on the same lot as the primary residence or primary home. They can be attached ADUs that are connected your main house, or created as conversion ADUs by repurposing existing space, such as a garage conversion, often from existing single family homes. Alternatively, they can be built as new detached units.
There are many benefits to building an ADU, both practically and financially. It’s often more affordable than traditional homes since it leverages existing property and infrastructure, avoiding costly new developments. An ADU can provide as much living space as a modern apartment, making efficient use of your property. ADUs can provide extra income through rental opportunities, support affordable housing, and help stabilize neighborhoods by increasing housing options. They can generate rental income to offset mortgage payments, offer a private space for family members like aging parents, diversifies housing options, and increase your property’s market value. Plus, it’s eco-friendly, reducing the need for new construction and supporting sustainable living, especially in areas that are in a housing crisis.
ADUs are secondary to the primary dwelling unit and are located on the same property or same lot as the main home, providing independent living while remaining connected to the primary residence.
Key Benefits of a Backyard Home
Increases Property Value | A well-built and thoughtfully designed ADU can boost the market value of your property, often 25%- 35% higher in urban areas. |
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Provides Housing for Family Members | Creates additional space for your family, regardless of their age or needs. |
Expands Current Living Space | Adapts to needs like home office, guest house, or studio, and can include other spaces such as kitchens, bathrooms, or living areas. |
Generates Rental Income | Provides passive income, offsetting costs or funding expenses. |
Overview of ADU Construction Methods
There are a few of different ways that your ADU can be constructed
When building an Accessory Dwelling Unit (ADU), you’ll need to decide on the construction method. Common options include traditional, prefabricated (prefab), modular, and panelized construction, each with its own pros and cons. There are also several types of ADUs to consider: detached ADUs (standalone buildings separate from the main residence), attached ADUs (units built by adding onto or transforming existing structures like walls, basements, or garages), and conversion ADUs (created by converting existing spaces within a home or accessory buildings such as garages or sheds). Junior ADUs (JADUs) are smaller units, often up to 500 square feet, typically attached or converted from existing space within a single-family home, sharing some facilities and subject to owner-occupancy requirements. ADUs can also be added to a multi family building, not just single family homes.
- Traditional Construction involves building from scratch on-site, offering high customization but often taking longer and costing more.
- Prefabricated Construction means the ADU is built in a factory and delivered, providing speed and cost savings but with limited design flexibility.
- Modular Construction builds sections in a factory for on-site assembly, balancing speed and customization.
- Panelized Construction uses pre-built panels assembled on-site, offering a middle ground in cost and time.
When converting existing structures, buildings such as garages or sheds can be repurposed into ADUs, maximizing the use of your property. At Type Five, our approach combines the best of both worlds, offering you design flexibility with the cost savings and convenience of prefab. Here are some of the notable features:
- Customizable: Every Type Five ADU is customizable online. You can select the size, color, layout, amenities, bedrooms, finishings, and more without paying thousands of dollars in design fees.
- Turn-Key Experience: Thanks to our streamlined process, you can ditch the chaos and stress of managing the complexities of building your backyard home. We’ll draw up your plans to meet building codes, get them approved by the city, and manage construction so you don’t have to. Our platform allows us to be your project's architect and general contractor, saving you enormous time and money while giving you the peace of mind that you're getting an amazing service and product.
- Efficient Construction Timelines: A traditionally built ADU can take dozens of subcontractors and operate under a more bespoke process to get your ADU built. We've streamlined the number of contractors involved, and run a repeatable, consistent process for every home we build. You can expect clear timelines, little to no back and forth, and weeks instead of months of construction on your property.
- Transparent Pricing: We guarantee your price right in our design process before you even submit a deposit. You can say goodbye to financial surprises & unexpected “change orders” because every project comes with a guaranteed maximum price before the building starts. This means you can accurately budget for the other things in your life… like your retirement or that vacation you’ve been thinking about!
What’s the bottom line? If you want a backyard home but don’t want to deal with the hassle and expense of traditional construction, then prefabricated/modular construction is the way to go. And if you want the convenience of prefab with the flexibility of custom design, then we’ve got your back.
The Process
As a property owner, how an ADU gets built will vary based on who you choose as your partner, but here are the general phases. The ADU development process involves several phases, from initial planning to completion, and each ADU project is unique. Understanding the development process helps ensure your ADU development meets your goals and complies with local regulations.
- A site feasibility study will help determine what can be built and where.
- Exploration and refinement of the interior layout
- Selection of finishes and materials
- Finalization of design plans
- Preliminary budgets and timelines assembled for review
- Preparation of permit documentation
- Submittal to local building department
- Addressing any inspection comments
- Receiving permit approval
- Pre-construction planning
- Site preparation and foundation work
- Framing and structural assembly
- Plumbing, electrical, and HVAC installation
- Interior and exterior finishing
- Inspections
- Moving in and settling phase
- 30-day follow-up inspection
- Seasonal maintenance check-ins
- Warranty service as needed
- Future upgrade opportunities
Skip the hassle with Type Five
Our turnkey approach makes it a breeze to avoid the complex process of designing, permitting, and building your backyard home. With us, you'll reduce costs, avoid delays, and get your project done faster.
Walnut Creek's ADU Regulations
Frequently asked questions about what you can build in Walnut Creek, based on state and local regulations.
Feasibility
Can I build an ADU on my property in Walnut Creek?
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.
Permitting
Do I need a permit for an ADU in Walnut Creek?
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.
How long does it take to get a permit for an ADU in Walnut Creek?
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.
Design
How many ADUs can I have in Walnut Creek?
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.
Is there a minimum lot size for a Walnut Creek ADU?
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.
Is there a minimum size for a Walnut Creek ADU
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.
How big of an ADU can I build in Walnut Creek?
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.
Can you build a two story Walnut Creek ADU?
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.
How many bedrooms can an ADU have in Walnut Creek?
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.
How close to the property line can I build a Walnut Creek ADU?
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.
Utilities
Does an ADU need its own electrical panel, water meter, or gas meter in Walnut Creek?
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.
Are fire sprinklers required in a Walnut Creek ADU?
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.
Is solar required on a Walnut Creek ADU?
You may be required to install solar panels on your ADU in Walnut Creek if your ADU is a newly constructed, non-manufactured, detached ADU. There are exceptions to the state energy code based on floor area and climate zone. In Walnut Creek (Climate Zone 12), ADUs 600sf or less can qualify for solar exemption.
Financials
How much can I rent an ADU for in Walnut Creek?
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.
Can an ADU be used as an Airbnb or short-term rental in Walnut Creek?
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.
Can your HOA prevent your ADU build 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.
How does an ADU affect property taxes in Walnut Creek?
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.
How much value does an ADU add in Walnut Creek?
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.
How much does it cost to build a Walnut Creek ADU?
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.
Online Resources
Learn more about building in Walnut Creek, California
City of Walnut Creek ADU Permitting Website
City of Walnut Creek ADU Municipal Code
