How to Choose the Right ADU Builder

There are general contractors, design firms, prefab ADU companies, & modular builders. Hillary Scott explains what to look out for when deciding on a builder
Updated July 01, 2021

In hindsight, Cottage’s Head of Contractor Partnerships and Bay Area native Hillary Scott wishes she knew more about what she was getting into when she embarked on a mission to remodel her house in Sunnyvale, California a few years ago.

“In the Bay Area, contractors are not hurting for work. After researching online and being referred to multiple contractors, it was still difficult to get a company to come on site to even give me a quote,” Hillary explained. “Between interviewing contractors, managing the architect, and getting buy-in on all finishes, it quickly became a second job. If it was challenging for someone who already works in the industry, I could only imagine how someone new to the process would feel.”

With her breadth of real estate experience in matching projects with the right build partner and project managers that are the best fit for the client’s needs, Hillary was just the right person to ask how to select the right builder for your accessory dwelling unit (ADU) plans, whether you're creating an attached ADU or a detached ADU.

Let’s jump right in!

Does Your ADU Builder Understand ADUs?


Despite her years of experience at real estate giant CBRE, Hillary could intuitively see the need for a better process for selecting build partners for residential construction. Her personal experiences with remodeling her own primary residence highlighted the need even further.

Now as Cottage’s Head of Contractor Partnerships, Hillary sources, vets, and onboards select ADU-specializing general contractors that are invited to join Cottage’s exclusive contractor network.

“With so many different parties involved in your ADU construction—architects, consultants, city permitting offices, and builders themselves—you want a team that knows how to navigate the whole system,” Hillary said. “Cottage carefully vets all potential contractors and ensures they are not only qualified to execute on our projects, but work seamlessly with all the different stakeholders.”

In Progress ADU Framing and Construction

With the updated ADU regulations being only a few years old, understanding the full ADU process is simultaneously important and not automatic within the construction industry from building permits and specific restrictions to local laws and ordinances. Make sure to confirm that your builder knows what does and does not apply to their ADU project before starting the project, warns Scott.

“ADU’s are becoming increasingly popular, but not every contractor is equipped to build these housing units,” Hillary explained. “It is imperative that contractors are comfortable executing on a project with a short timeline, with a tight schedule and little room for error.”

Does Your Builder Understand Your ADU Design and Needs?

With the traditional ADU building process, the design and construction teams are typically separated—the architect designs the permit set and navigates the local permitting process, and then the builder comes in after permit approval to bid on your project. This is a risky bet.

“Because there is little to no communication between the designer and builder, it’s difficult to get a clear cost estimate for your project until you have paid tens of thousands out of pocket,” Hillary explained. “That can be a non-starter for most single family homeowners.”

In Progress ADU Framing and Construction Attached ADU General Contractor

On the opposite end of the spectrum, prefab ADU companies and modular home providers such as Villa Homes and Abodu bridge that connection issue in-house by building their units off-site and craning them in. However, that comes with severe trade-offs as well.

“With prefab ADUs or modular homes, you’re stuck with the set design,” Hillary said. “Part of what makes ADUs so appealing is the ability to build a completely new living space without buying a whole new home. We have found that most homeowners want something customized, something that matches their current home. Cottage brings the contractor in early in the design process, requesting options to value engineer the design and get the best possible cost for the homeowner without having to sacrifice customization.”

With its in-house design and operations teams working hand-in-hand with select ADU construction partners, Cottage team is able to provide the best of both worlds—custom granny flats designs tailored to the homeowner’s specific needs and upfront cost estimates from its general contractor network before committing a dollar to the project.

Is the ADU Construction Quality Exceptional?

“Building high-quality construction is foundational for us at Cottage,” Hillary says. “The real standout GCs are the ones that are highly communicative, experienced, localized, and dependable.”

With projects ranging from second homes for family members, home offices, or a new art studio to rental income ADUs like Airbnbs, Cottage has designed and built high quality ADUs for the full range of ADU use cases.

“We match the right general contractor partner to your ADU project,” Hillary said. “Having been on the other side trying to do my own remodeling projects, having a quality contractor personally assigned to my project would have been a game changer. ”

Completed ADU Interior Window Drywall Detail General Contractor

Just like your existing residence, custom, stick-built ADUs are constructed to last decades. As a result, every detail matters. Having a solid foundation, wood framing, drywall, roofing, and custom finishes are a given for Cottage general contractor partners. This should be a requirement for your project as well, and is not necessarily the case for prefab home and ADU companies such as Abodu, Villa Homes (formerly Habitat ADU), and other providers.

Is Project Capacity Guaranteed for Your ADU Project?

Because smaller general contractors tend to be driven by local demand, it can be difficult to find a good contractor willing to take on your project for a fair price.

“Cottage looks for contractors that we can build a long term relationship with through a steady stream of projects in their location of expertise,” Hillary explained. “We are committed to learning what projects work best for each contractor as these relationships are critical in being able to offer our clients the best contractors, committed to helping build our projects.”

Larger contractor firms tend to shy away from ADU projects because of their smaller project size compared to full-sized homes and home remodels. In addition, there can be additional hidden costs associated with trying to work with a larger-scale contractor.

“My personal project was fairly significant, however was still too small for many of the contractors in my area,“ Hillary said. “By providing our contractor partners with ongoing projects and a process to help streamline the building process at Cottage, we are able to get these quality contractors to take on these relatively smaller projects that they may not be as willing to do as one-off projects.”

ADU In Progress Construction Foundation Detail

Even prefab ADU companies have capacity issues. Certain companies require a certain number of prefab accessory dwelling units in your neighborhood to be signed under contract before starting on your project, leaving you at the whims of local demand that is out of your control.

Alternatively, other prefab ADU companies may not be able to definitively confirm whether your project site qualifies for a static ADU to be craned in. Site conditions out of your control such as electrical power lines, easements, minimum lot size, or your lot depth can either prevent a prefab ADU from being dropped in or add in hidden costs that can show up last minute.

Are ADU Delivery Timeline and Expectations Clear?

Once you have settled on a general contractor or other ADU provider, timeline expectations are important to confirm up front. Of course, situations such as the recent pandemic have put some things out of control, but issues such as timeliness, customer service, communication, and construction quality should not be on the table.

“The timeline to complete an ADU project is pretty tight!” Hillary said. “The Cottage Design and Operations teams are constantly fine-tuning our process to ensure a beautiful, buildable design that will quickly pass through the city and get into the contractors hands as soon as possible.”

“By keeping our contractor in the loop throughout the process, we can keep the entire team on the same page and limit any surprises in the field. This keeps your project on schedule.”

The contractor or firm should be able to provide you with a clear sense of construction deadlines and expectations up front. Even then, contractors that have little to no information about your specific ADU design may not be able to provide you with an accurate estimate, both for cost and timing.

Choosing the Right ADU Builder for your Cottage

Whether you are choosing between a stick-built ADU through the old-fashioned general contractor route or considering the prefab ADU route, there are hidden issues along the way across CA from San Diego to San Jose that we covered in this article. State laws and jurisdictions, zoning laws in your municipalities, and building permit applications are just some examples of ADU considerations you should be aware of for any new constructions or renovations to your existing structure.

In contrast, Cottage’s A-to-Z process from eligibility to design to permits to construction minimizes the question marks you have before committing to your ADU project. There are so many types of ADUs from in-law apartments to a backyard home for rent to basement conversions, garage conversions, in-law units, and everything in-between. The best ADU contractor guarantees that your backyard cottage or attic apartment will include a full-service design that's perfect for your lifestyle and your neighborhood's building codes.

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