An ADU can solve a lot of problems at once. You might need space for a parent who wants independence but still wants to be close. You might want a rental unit to offset housing costs. Or maybe you want a quiet place to work that feels separate from the main house.
And many homeowners are already doing exactly that. Freddie Mac estimated in 2020 that about 1.4 million single-family properties included an accessory dwelling unit.
This guide explains how to choose an ADU contractor you can trust, what kind of services to expect, which questions to ask, and how to avoid budget surprises.
In most ADU projects, the general contractor or design-build team manages the build and coordinates the trades, schedule, and inspections. Depending on the scope of your project, services may include:
An ADU touches almost every trade and requires the coordination of multiple professionals to successfully complete a project.
ADU contractor or general contractor: Oversees the overall project and coordinates trades, schedules, and inspections.
Architect or designer: Often needed for plans that meet zoning rules, egress requirements, and structural needs.
Engineer: May be required for structural calculations, foundation design, or seismic and wind requirements that the structure must meet.
Licensed plumber: Needed to install any water or gas lines associated with the plumbing system in your ADU.
Licensed electrician: Installs any electrical wiring or equipment associated with the electrical system.
ADUs are regulated and detail-heavy. You want someone who can build safely, document everything, and manage approvals without constant delays.
An ADU is typically treated as a dwelling unit, which means it involves structural work, plumbing, electrical work, and inspections. So, when hiring a contractor to build your ADU, you need to ensure that they have the proper licenses to work on the project.
Ask the contractor:
If your potential contractor avoids the first question or answers the third question vaguely, this is a sign to step back.
Insurance matters here because the ADU contractor will likely need to hire various subcontractors, work with heavy machinery, and have longer timelines.
Ask for proof of general liability coverage. Also, confirm that the contractor’s employees are covered by workers’ compensation and that all subcontractors are properly licensed and insured.
ADUs come in many forms, including:
Each type has its own set of challenges. To make sure they have relevant experience, ask to see examples of ADUs similar to yours in size and layout, lot constraints, utility tie-ins, and permitting process.
Although there is no universal “ADU certification,” professional contractors often have:
Also, if your area requires energy documentation or specific construction standards, ask how they handle those requirements.
If you’re trying to hire the best ADU contractor in your area, look for online reviews that mention:
Another factor to consider is how many active projects the contractor has at the same time. If they are currently overworked, this could potentially delay the completion of your ADU.
Preparing a list of questions to ask ADU contractors can save months of delay and confusion.
Ask:
Then ask questions that protect your budget:
ADU costs vary a lot. As a rough planning range, many projects fall somewhere around $150 to $300 per square foot, but detached new builds, difficult sites, long utility runs, and higher-end finishes can push that well above the average. (Remember that square-foot pricing is a useful shortcut, not a guaranteed final number.)
Here are some of the factors that can swing the price:
If you’re unsure how to hire an ADU contractor, start by getting two to three detailed bids. More than that often adds noise, not clarity.
Make sure each bid covers the same scope. For example, one contractor might include full permitting and design coordination, while another might not.
A good ADU estimate should clearly spell out the details you need to compare proposals:
If the estimate is one page with a single number, it is not detailed enough for an ADU.
Clarify whether the following items are included or not:
ADU rules usually come from a mix of state law, local zoning, and building code enforcement, so the exact standards can vary widely by city and county. That said, common considerations include:
Even an experienced ADU contractor should verify local requirements early because rules can change.
Skipping permits or building without approvals can create serious legal and resale issues in the future.
California has been one of the country’s most active ADU markets. The state continues to update its ADU rules. Most recently, changes clarified parts of the permit process, impact fee rules, and the handling of some older unpermitted units. They also expanded some ADU allowances on lots with existing multifamily housing.
In California, local agencies generally must tell applicants within 15 business days whether an ADU application is complete. Once the application is complete, they generally have 60 days to approve or deny it.
Homeowners researching tips for choosing a reliable contractor for home renovation projects often underestimate the complexity of ADUs. These mistakes can lead to cost overruns and delays:
It can take time to find an ADU contractor who understands zoning, permitting, and utility coordination. Renovate helps make it easier for homeowners to get started.
Why use Renovate?
Timelines depend on the project type and how quickly the permitting process moves. Construction may take several months, depending on the scope of the project, while the total process from design, plan review, and inspections can take longer.
It depends on local rules and how you plan to use the ADU. In some areas, ADUs can share utility lines between the main house and the ADU. Others may require separate metering or have specific requirements for electrical capacity and water connections.
A contractor should review local utility rules early so they do not get surprised by connection fees or upgrade requirements after the construction has started.
Sometimes a qualified designer or draftsperson prepares an ADU project. However, if the layout is more complex or local rules require more detailed plans, then an architect might be necessary. A good contractor should tell you early what level of design help your project needs.
An ADU contractor is often a general contractor who regularly handles ADU work, including permitting, utility coordination, inspections, and other unique project requirements. A general contractor may be able to build an ADU, too, but not every GC has real ADU experience.
There are many factors that affect how long it takes to get an ADU permit, including your municipality, project complexity, and whether the permit office requires corrections after reviewing your plan. Some permits move faster than others, but ADU approvals often take longer than homeowners expect because zoning, utilities, structural details, and permit office backlog can all affect timing. A contractor with local ADU experience should be able to give you a realistic timeline upfront.
