How to Hire an ADU Contractor

Hiring the wrong contractor is the single biggest way an ADU project goes sideways. Not bad luck, not surprise soil conditions, not the city permit office. It's the contractor.

The good news is that most contractor problems are avoidable with better screening upfront.

What Kind of Contractor Do You Need?

For most ADU projects, you want a licensed general contractor with documented ADU experience in your specific city. Some contractors specialize exclusively in ADUs. Others are general residential builders who do ADUs as one project type among many.

ADU specialists often know the local permit office, use pre-approved plan sets, and have subcontractor relationships already in place. That can translate to faster timelines and fewer surprises.

For simple garage conversions, a design-build ADU firm or an experienced general contractor is typically sufficient. For complex sites or larger builds, an architect working alongside the GC adds oversight that pays for itself.

Licensing and Insurance

This is non-negotiable. Before anything else:

• ›Verify the contractor's license at the California Contractors State License Board (cslb.ca.gov). Enter their license number and confirm it's active, in good standing, and in the correct classification (B-General Building or C-class specialty as appropriate)
• ›Ask for a certificate of general liability insurance ($1 million minimum) and workers' compensation insurance
• ›Confirm the policy is current, not expired

Working with an unlicensed contractor voids your homeowner's insurance coverage for construction-related damage and leaves you personally liable for injuries on the job site.

Get Multiple Bids

Three bids is the minimum. The goal isn't just to find the lowest price. It's to understand the actual scope of work, catch gaps in coverage, and identify contractors who are thorough versus those who bid low to win the job and make it up in change orders.

When you send out bid requests, provide the same information to each contractor: the site address, your desired ADU type and approximate size, and any constraints you know about. If you already have plans, share them.

When the bids come back, compare them line by line. A well-structured bid breaks out:

• ›Site prep and demolition
• ›Foundation
• ›Framing
• ›Roofing and exterior
• ›Electrical, plumbing, HVAC
• ›Interior finishes
• ›Permits and fees

A bid that's just one lump number with no breakdown is a red flag.

Questions Worth Asking Every Contractor

How many ADUs have you completed in this city specifically? Local permit experience matters. A contractor who has pulled permits in Los Angeles will have an easier time than someone doing their first project there.

Can I see two or three completed projects and speak with those homeowners? References from recent projects are more useful than a portfolio of photos. Ask the homeowners about the timeline, whether the final cost matched the estimate, and how the contractor handled problems when they came up.

Who will be on site every day? Some GCs manage multiple jobs simultaneously and are rarely on your site. Know who is supervising day-to-day and how often the GC will be there in person.

What does your payment schedule look like? Legitimate contractors typically structure payments around milestones: deposit at start, payment at framing completion, payment at rough-in inspections, final payment at completion. Be cautious of any contractor asking for 50% or more upfront.

What's your process when something unexpected comes up? How they answer this tells you a lot. Problems always come up. A contractor who explains a clear change order process is more trustworthy than one who says "we'll figure it out."

Red Flags

These aren't guarantees of a bad outcome, but each one warrants serious caution:

• ›Pressure to decide quickly: "I have another client interested in this slot" is a classic high-pressure tactic
• ›Unusually low bid: If one bid is 30% lower than the others with similar scope, either they're planning change orders or they've missed something
• ›Large upfront payment required: $5,000–$10,000 is reasonable as a deposit on a large project. $50,000 upfront before work starts is not
• ›No written contract: Everything needs to be in writing, including scope, schedule, change order process, warranty, and payment terms
• ›Can't provide references: If a contractor can't connect you with recent ADU clients, that's a problem
• ›Asks you to pull the permit as owner-builder: Some contractors use this to avoid the license requirement and shift liability to you. Don't do it unless you genuinely intend to manage the project yourself

The Contract

Before any work starts, you should have a written contract that includes:

• ›Full scope of work with specifications
• ›Timeline with milestones
• ›Payment schedule tied to milestones
• ›Change order process (what triggers one, how they're priced, what requires your written approval)
• ›Warranty terms on labor and materials
• ›What happens if either party terminates the contract

California law requires any home improvement contract over $500 to be in writing. For an ADU project, your contract should be detailed enough that a third party could pick it up and understand exactly what was agreed to.

One More Thing

The cheapest bid rarely produces the best outcome. But neither does the most expensive. The contractor who earns the job should be the one who demonstrates they've done this before, communicates clearly, and gives you a contract that protects both sides.

Ask questions. Check the license. Call the references. The extra two weeks of due diligence is far less painful than six months of problems on a job site.