A guide for building backyard homes in Walnut Creek, 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. It can be attached to your main house, converted from an existing structure like a garage, or built as a new detached unit, such as a backyard cottage or granny flat. This makes it a versatile housing solution tailored to your needs, whether for guests, family, or tenants.
Building an ADU can be a practical and financially smart choice. It’s often more affordable than traditional homes since it leverages existing land and infrastructure, avoiding costly new developments. An ADU can provide as much living space as a modern apartment, making efficient use of your property. It can generate rental income to offset mortgage payments, offer a private space for family members like aging parents, 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 with housing shortages.
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. |
Generates Rental Income | Provides passive income, offsetting costs or funding expenses. |

Overview of Construction Methods
There are a couple of different ways that your ADU can get built
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.
- 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.
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, 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
How an ADU gets built will vary based on who chooses as your partner, but here are the general phases.

- 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
Walnut Creek's ADU Guidelines
Frequently asked questions about what you can build in Walnut Creek
Can I build an ADU on my property in Walnut Creek?
Do I need a permit for an ADU in Walnut Creek?
How long does it take to get a permit for an ADU in Walnut Creek?
How many ADUs can I have in Walnut Creek?
Is there a minimum lot size for an ADU in Walnut Creek?
Is there a minimum size for an ADU in Walnut Creek?
How big of an ADU can I build in Walnut Creek?
Can you build a two story ADU in Walnut Creek?
How many bedrooms can an ADU have in Walnut Creek?
How close to the property line can I build an ADU in Walnut Creek?
Does an ADU need its own electrical panel, water meter, or gas meter in Walnut Creek?
Are fire sprinklers required in an ADU in Walnut Creek?
Is solar required on an ADU in Walnut Creek?
How much can I rent an ADU for in Walnut Creek?
Can an ADU be used as an AirBnB or short-term rental in Walnut Creek?
Can your HOA prevent your ADU build in Walnut Creek?
How does an ADU affect property taxes in Walnut Creek?
How much value does an ADU add in Walnut Creek?
How much does it cost to build an ADU in Walnut Creek?

Online Resources
Learn more about building in Walnut Creek, California
City of Walnut Creek ADU Permitting Website
City of Berkeley ADU Development Standards Cheat Sheet
City of Walnut Creek ADU Municipal Code