The 12 Best ADU Builders in the Bay Area

May 23, 2022

Photo by Fleur on Unsplash

Finding the best ADU builders in the Bay Area begins with research. Whether asking friends and family, reading provider websites online, or asking other ADU owners in forums, this essential step helps prepare you for the many important decisions you’ll have to make in the planning process. Here, we’ll provide an overview of the 12 best ADU builders in the Bay Area: Six prefab ADU builders and six site-built ADU builders.

The difference between a prefab and site-built ADU

There are significant differences in process, time, budget, and customization between a prefab and site-built ADU.

A site-built ADU, also called a stick-built ADU, is built on-site. While they can be built to your precise specifications, that kind of customization comes at a price. It will take longer and cost more to build an ADU in the design of your choosing. Plus, the work needs to be completed on-site at your home, which can be disruptive to your daily life. They’re also more likely to be delayed by inclement weather because of the amount of time spent on-site.

Prefab ADUs eliminate much of the cost associated with a site-built ADU by offering their own designs. Many ADU companies offer a few designs to choose from alongside customizable finishes and interior and exterior colors. Their modular construction means that these homes are built offsite, minimizing disruptions to your daily life and minimizing potential delays due to bad weather and other factors. All these factors truncate the timeline and offer significant cost savings as well.

The 6 best prefab ADU companies

If you want to build an ADU while saving time, money, and headache, a modular prefab ADU is the way to go. These specialty firms are solely focused on modular ADU builds, often offering additional helpful services to help with project management, furnishings, and other related services. The six Bay Area prefab ADU companies below are possibilities as you explore your options.

Axiom ADU

Based in Berkeley, Axiom ADU offers prefab units across the Bay Area. With roots in construction, Axiom offers detached ADUs (DADUs) along with garage conversions, basement conversions, and attached ADUs. The firm offers start to finish services, with design, project management, accounting, and construction professionals on staff to help move things along. They also offer customization options to help match the property to your home. 


Spacials Studio ADU
Photo by Spacial

Stellar customer service, seamless planning, simplified steps: Spacial’s ADU construction services make the process as easy as can be.

At Spacial, we offer studio and one-bedroom ADUs designed from the inside out to maximize space without taking up too much of your property. Each ADU meets LEED requirements, is Passive House certified, and is equipped for solar panel outfitting too. Our close collaboration with world-renowned architecture firm CAZA puts smart, modern, and bright designs front and center, while our partnership with leading modular builder Groudon brings their expertise to your project.

Spacial offers a full staff of project managers who handle every step for you from beginning to end. You won’t need to call other professionals, get permits, or schedule any appointments. We do all the heavy lifting while you go about your daily life. Your dedicated Spacial consultant has the whole process under control. 


Based in San Francisco, Shilo designs and builds ADUs for Bay Area clients. The company, founded in 2018, constructs ADUs from 200 to 1,200 square feet. Green practices are at the heart of Shilo’s designs: Their ADUs meet both LEED and Passive Home certification requirements, and they come ready to install PV solar panels for additional savings. Known for their elevated, polished, and modern designs, Shilo also offers fully managed services to help with design, installation, and project management. 

Bay Modular

This full-service modular ADU company based in Hayward, California, is known for upcycling old shipping containers for use as ADUs. These designs are pre-approved by local authorities, avoiding the permitting process. The homes, called the Solo series, begin at 320 square feet, with multiple sizes and configurations available. Notably, site preparation costs, such as delivery and installation costs, are not included in the initial price.


Home automation is central to Veev’s ADU designs. Each unit is automatically equipped with smartphone-enabled controls for lighting, climate control, doorbells, blinds, and bathroom features. At the time of writing, Veev offers one model: a 568-square-foot, one-bed, one-bath ADU. The company, based in San Mateo, also builds multi-family homes and townhomes.

California Modulars

This San Jose-based ADU builder offers multiple prefab ADU starting at 400 square feet and up to 1,450 square feet. The company offers a full suite of services, including help with permits, relationships with local lenders, and customizable finish options. California Modulars is unique among prefab ADU builders in that they also offer stick build options. 

The 6 best site-built ADU companies in the Bay Area

Person using a welding machine
Photo by Christopher Burns on Unsplash

If you want to build a fully customized ADU from the ground up, you’ll need to work with a site-built ADU company. These companies are often general contractors or other construction experts who have strategically pivoted their expertise to service clients in need of ADUs. These six site-build ADU companies below are often cited as leading options for Bay Area homeowners in search of a trustworthy contractor.

BMF Construction

This San Francisco-based general contractor manages the construction process from start to finish for all types of structures, including ADUs. Their staff assists with all parts of the project, such as daily project supervision, permit processing, and arranging inspections. The company serves the greater San Francisco area.

HDR Remodeling

This award-winning, full-service residential design-build contractor has recently expanded its repertoire to include ADUs. Specializing in both garage conversions and standalone detached ADUs (DADUs), HDR Remodeling has experience designing ADUs that can tackle any number of presented challenges. HDR Remodeling’s service area is limited to the East Bay.

Design Draw Build

Design Draw Build is an architect-led design-build company that has added ADUs to its lineup of offerings. Drawing on their stated commitment to social justice and sustainability, the company views ADUs as an important tool to fill the gap in affordable housing that affects the Bay Area.  As a stick-build ADU company, Design Draw Build works closely with clients to design an ADU that works with their current surroundings and structure. 

McDunn ADUs

Unlike many other stick-build companies on this list, McDunn ADUs focuses exclusively on designing and building ADUs. Based in Berkeley, the firm brings several years of experience in whole house remodeling and other construction projects to ADU clients. McDunn ADUs services clients in the East Bay.

Oliver Builders

This residential building and remodeling company has experience constructing several types of ADUs, including detached ADUs and attached ADUs. Working with a team of skilled subcontractors, Oliver Builders collaborates closely with the client and their architect to bring their ADU vision to life. The firm, based in Berkeley, is a Certified Green Builder that uses best practices when it comes to construction’s impact on the environment.

Canyon Design Build

A general contractor, Canyon Design Build offers ADUs among many other home styles. The full-service building and remodeling company has all the necessary professionals on its team, simplifying the ADU building process. The firm also has a long history of forward-thinking, environmentally-friendly builds, a tradition it continues today with LEED-certified professionals.

Are prefab ADUs long-lasting?

Greenhouse with colorful folding chair
Photo by Arno Smit on Unsplash

Although they may not be built like a traditional home, prefab ADUs are not temporary by any measure. They are constructed to the same standards as any other home and are subject to inspection and permitting before anyone can live in one. You can expect to get many, many years of use out of your ADU.

How much does it cost to build an ADU in the Bay Area?

The cost to build an ADU in the Bay Area can vary wildly. Your cost will depend on the model you choose, the company you go with, and the finishes you select. There may be other considerations not initially predicted at the beginning of the ADU construction process.

The average spend to construct an ADU in California is $250 per square foot, but that cost increases when it comes to Bay Area projects. Expect to spend anywhere between $350 and $900 per square foot on an ADU in the Bay Area once all is said and done. The total cost can clock in anywhere between $250,000 and $500,000, depending on the size of the ADU, finishes, and other factors. Generally, prefab ADUs will cost less than stick-built ADUs.

How do I start the ADU building process?

With recommended providers and costs in hand, you’re well prepared to begin your ADU process. But before a shovel hits the ground (or in Spacial’s case, the walls assembled in a warehouse offsite), there are some important decisions you have to make.

  • Decide which model is better for your needs. Do you want a fully customized build from the ground up, or do the time and cost savings of a prefab ADU appeal to you? Do you want to build an attached ADU, which would require a stick build, or do you prefer a detached ADU through a prefab builder that checks all the boxes? This decision needs to be made before you can select the best ADU builder for your needs.

  • Consider your space. The amount of physical space you have can shape which ADU you select. A small backyard may only have space for a 400-square-foot studio, while larger yards can accommodate larger homes.

  • Determine your budget. The type of ADU you want to build and how much space you have are two major factors when it comes to crafting an estimated budget. Keep in mind that costs can quickly spike when you’re creating a custom ADU, so these transparent conversations are important to have with your chosen builder.

  • Review and select a provider. With a budget and a general direction in mind, give a few ADU builders a call. Don’t be afraid to ask questions about their process, approach, and how they’d manage your project. You can ask them about cost control as well and the measures they have in place to make sure you don’t run over budget.

  • Decide how you’re funding your ADU project. Once you know your budget or you’ve obtained a quote, it’s time to secure your funding. There are many ways to fund an ADU, including through a home equity line of credit (HELOC), home equity loan, and cash.

Once these determinations are made, the actual ADU construction process can begin. And when you work with a partner like Spacial, you won’t have to lift a finger. Our team handles every step, from permitting to scheduling, and keeps you informed at each turn.

Build your Bay Area ADU with Spacial

External side view of Spacials One Bedroom and Studio ADUs
Photo by Spacial

Spacial’s turnkey ADU solutions make Bay Area ADU building a breeze. Our modern studio and one-bedroom models, designed by leading architecture firm CAZA, eliminate the design process, saving you time and money. Each unit is fully assembled off-site: We only need to be on your property to pour the foundation and crane your ADU into place. That means minimal disruptions to your routine. So whether you’re looking to earn extra income, house aging family members, or build a private working space in your backyard, a Spacial ADU fills that need.