How to Hire a ADU Contractor in San Francisco: A Step-by-Step Guide

How to Hire a ADU Contractor in San Francisco: A Step-by-Step Guide

The question most San Francisco homeowners forget to ask their contractor is simple: “How many projects do you currently have in DBI review?” If the answer is more than eight, your project goes to the back of a very long line. San Francisco’s Department of Building Inspection is the busiest permit office in the Bay Area, and a contractor who has already flooded it with ten or fifteen pending permits is not going to prioritize yours. This guide will walk you through exactly how to find, vet, and hire an ADU contractor in San Francisco, what a legitimate bid should look like, and which answers should make you quietly cross a name off your list. For more guides & resources, explore our blog.

Call (424) 328-5746

Quick Answer

Hiring an ADU contractor in San Francisco comes down to three moves: check their license and DBI workload before you meet, demand a written line-item price before you sign, and read the contract for scope, payment schedule, lien releases, and a 365-day warranty clause. Skip any of those and you’re gambling. The contractor you want is one who can name their permit history, has a manageable DBI queue, and puts every single number in writing before demo day ever arrives.

Table of Contents

• The Three ADU Contractor Models (and Which One Fits Your Project)
• How to Read a CSLB License Lookup Like a Contractor
• The 12-Question Vetting Script
• What a Written Contract Must Contain
• How to Compare Bids That Use Different Spec Levels
• The Step-by-Step Hiring Process
• Common Mistakes to Avoid
• Frequently Asked Questions

The Three ADU Contractor Models (and Which One Fits Your Project)

Before you start dialing, understand that “ADU contractor” in San Francisco is not one job title. It’s three different business models wearing the same hat, and each one fits a different kind of project and homeowner.

Model 1: The General Contractor (GC)

A general contractor runs the whole build: they hire the plumber, schedule the electrician, order the lumber, pull the permits, and answer the phone when your neighbor asks why there’s a concrete truck on Roslyn Terrace. You hire a designer or architect separately, then hand those plans to the GC to build. This is the traditional route and it works well for custom, site-built ADUs where you want specific materials, a specific layout, or a garage conversion that requires structural gymnastics. You become the project manager of your own schedule, meaning you coordinate between the architect and the builder. If you’re disciplined and have time, this route gives you the most design freedom.

Model 2: The Design-Build ADU Firm

A design-build firm handles both the design and the construction under one roof. One contract, one point of contact, one phone number to call when something looks wrong. This is the model we operate under at Benson ADU Builders in San Francisco, and it’s the right fit for most homeowners because it removes the blame game between architect and builder when a wall moves three inches. Design-build firms typically have standardized floor plans they can adapt to San Francisco’s narrow lots and weird setbacks, which keeps design costs lower than hiring an architect for a fully custom job. If you want to add an ADU without turning your life into a part-time construction management job, this is the model to lean toward.

Model 3: The Prefab-Brand Authorized Installer

This is the wildcard most San Francisco homeowners don’t know exists. Prefab manufacturers like Cover, Dvele, and Boxabl build ADU modules in a factory, then ship them to your site where an authorized installer handles the foundation, utility hookups, and finishing work. The advantage is speed: a factory-built module can arrive weeks faster than a site-built ADU because the weather doesn’t stop a factory line the way it stops a framing crew in the Outer Sunset. The trade-off is flexibility. Prefab ADUs come in fixed sizes and configurations, so if your San Francisco lot has a 4-foot side setback on one side and a 6-foot on the other, you need a brand whose modules actually fit. Ask any prefab installer which brands they’re authorized to work with and get that answer in writing. “We can do anything” is not an authorization.

Which model fits? If you’re building a custom unit and want total design control, hire a GC. If you want one throat to choke and a streamlined process, go design-build. If you want speed and your lot fits a factory module, explore a prefab installer. There’s no universally correct answer, only the correct answer for your lot, your budget, and your patience for managing subcontractors. See our ADU Cost Breakdown: The San Francisco Homeowner’s Reference for 2026 to match model to budget.

How to Read a CSLB License Lookup Like a Contractor

The California Contractors State License Board database is public, free, and the single most underused tool in San Francisco ADU hiring. Most homeowners glance at it and see “Active” and move on. Here’s what actually matters.

Step 1: Confirm the License Number Matches the Name

Type the license number into the CSLB lookup and check that the name on the license matches the name on the contract. Not the name on the logo. Not the name the salesperson gave you. The legal name on the license. If the person signing your contract isn’t the license holder or an officer of the licensed company, walk away. A license is not transferable, and an unlicensed signatory is a legal red flag.

Step 2: Check the Field and Classification

You want a “B” General Building classification. That’s the license class that covers ADU construction. An “A” license is engineering, “C” licenses are specialty trades. A company with only a C-36 plumbing license cannot legally build your ADU. They can do the plumbing inside it. They cannot be the prime contractor.

Step 3: Look at the Founding Date vs. the License Issue Date

If a company claims 15 years of experience but their license was issued 14 months ago, ask why. There are legitimate reasons: a company restructures, re-licenses under a new entity, or an owner splits off. But you should know before you sign, not after. And if the company has only been licensed for a year and the owner doesn’t have a solid answer for what they did before, that’s a risk signal.

Step 4: Check Worker’s Comp Status

The CSLB listing shows whether the contractor carries workers’ compensation insurance. If it says “exempt,” that means the company claims it has no employees and the owner does all work personally. For an ADU project that requires a crew of five for four months, that answer is not just wrong, it’s a liability transfer to you. If a worker gets injured on your property and the contractor doesn’t have workers’ comp, your homeowners insurance becomes the piggy bank.

Step 5: Read the Complaints and Legal Actions

The CSLB database lists formal complaints and disciplinary actions. Don’t overreact to a single dispute from 2018. Construction is messy and disputes happen. But if you see a pattern of multiple complaints about abandonment, unlicensed work, or failure to pay subcontractors, that pattern is your answer. The database is there to be read.

The 12-Question Vetting Script

This is the part most guides gloss over. They say “check references and read reviews” and leave it there. That’s not vetting. That’s window shopping. Here are twelve specific questions to ask every contractor bidding on your San Francisco ADU, with the answers that should disqualify them.

Question 1: How many projects do you currently have in DBI review?

This is the opener we mentioned at the top. If the answer is more than eight, ask how they sequence their work. A contractor running a dozen concurrent permits is not giving your project their attention. Red flag: any number above twelve.

Question 2: How many ADU permits have you pulled in San Francisco in the last two years?

San Francisco has its own permit office culture, and it’s different from Oakland or Daly City. You want a contractor who has navigated DBI recently, not someone whose last San Francisco permit was in 2019. Red flag: zero, or an answer that pivots to “we’ve done lots of other projects.”

Question 3: Who is the project manager assigned to my job, and how many projects do they currently run?

The owner sold you. The project manager builds it. Meet that person before signing. Red flag: “You won’t meet them until we start.”

Question 4: Do you use written change orders, and what triggers one?

Change orders are legitimate. Surprises happen behind walls. But they must be written, signed by you, and priced before work continues. Red flag: “We just handle it as we go.”

Question 5: Can I see a recent San Francisco ADU project budget with the final number next to the original bid?

You want proof that their initial numbers hold. Red flag: refusal to share any real numbers from past projects.

Question 6: Who exactly will be on my property each day? Are they employees or subs?

Subcontractors are normal. But you should know who answers for them. At Benson ADU San Francisco, every technician on site is background-checked and uniformed, which means you never have to guess whether the person in your driveway is actually part of the crew. Red flag: “I can’t tell you who’ll show up.”

Question 7: What’s your current timeline from permit submission to DBI approval?

San Francisco’s DBI approval timelines vary, and any contractor who promises a specific week count is guessing. What you want to hear is their real recent experience: “Our last three projects took between four and seven months in review.” Red flag: a precise promise like “eight weeks, guaranteed.”

Question 8: How do you handle utility coordination with PG&E and SFPUC?

ADUs frequently require new or upgraded utility connections. This is where schedules go to die in San Francisco. Red flag: “Don’t worry about it.”

Question 9: What warranties do you offer, and what’s the term?

Listen for a specific number and a specific scope. A one-year workmanship warranty is industry standard. We provide a 365-Day Done Right Promise on every project in writing. Red flag: “We stand behind our work” with no number attached. Our ADU Builders Maintenance Checklist for San Francisco Homeowners shows what to track during that first year.

Question 10: Will you provide lien waivers at each payment milestone?

Lien waivers protect you from the scenario where your contractor doesn’t pay a sub, and the sub comes after your house. This is non-negotiable. Red flag: “You don’t need those.”

Question 11: Can you give me three references from San Francisco ADU projects finished in the last 18 months?

Not from 2021. Recent, local, ADU-specific. Red flag: all references are conveniently “out of town right now.”

Question 12: What don’t you do?

Every good contractor has a limit. A contractor who says “we do everything” is a contractor who will learn on your dime. Red flag: not one honest limitation.

What a Written Contract Must Contain

A verbal promise is a rumor between two people. A contract is a document a judge can enforce. In California, any home improvement job over $500 legally requires a written contract. Your ADU is a six-figure project. The contract is not a formality. Here’s what must be in it, line by line.

1. Scope of Work, Written to the Square Foot

“Build an ADU” is not a scope. The scope is: a 480-square-foot detached ADU at 1427 Kirkham Street, including one bedroom, one bathroom, a kitchenette with specified materials, flooring type, window count and sizes, exterior cladding specified by brand and model, roof type, and paint colors. If it’s not written down, it’s not included. If it’s ambiguous, it becomes a change order later.

2. A Payment Schedule Tied to Milestones, Not Dates

The California legal maximum deposit for home improvement is 10% or $1,000, whichever is less. After that, payments should tie to work completed: foundation poured, framing passed inspection, rough electrical signed off, drywall up, final inspection passed. Never agree to a payment schedule based on calendar dates. Dates slip. Milestones are objective. And never pay for work that hasn’t been completed and inspected.

3. A Lien Waiver Schedule

At each payment milestone, your contractor should provide conditional and unconditional lien waivers from themselves and their subs. This is the legal mechanism that says “I got paid and I release my right to put a lien on your property.” Without it, you can pay your contractor in full and still find a subcontractor filing a lien against your house because the GC never paid them. That’s not a hypothetical. It happens in San Francisco every year.

4. Change Order Procedure

The contract should state that any change to scope, price, or schedule requires a written change order signed by both parties before the work begins. This cuts both ways. It protects you from surprise charges, and it protects the contractor from scope creep from a homeowner who thinks “while you’re here, can you also…” is free. The clause should be short and plain: “No oral modification shall be valid. All changes require a written change order signed by both parties.”

5. A 365-Day Warranty Clause

Every ADU should come with a written workmanship warranty for at least one year. Read the exact language. “We warrant our work against defects in workmanship and materials for a period of 365 days from substantial completion” is a real warranty. “We’ll make it right” is not. We stamp our 365-Day Done Right Promise on every contract we write, with a free second visit if any covered repair fails. That’s the standard you’re looking for.

6. Insurance Certificates

General liability and workers’ compensation certificates should be attached to the contract, not promised later. If a contractor hesitates to provide an insurance certificate before work starts, that hesitation is your answer.

How to Compare Bids That Use Different Spec Levels

Three bids land in your inbox. One is $180,000. One is $225,000. One is $290,000. The instinct is to take the bottom number and run. But here’s the thing: those three bids are not quoting the same project. They’re quoting three different interpretations of the same conversation. Here are the four line items where low bids hide cost overruns.

Line Item 1: Foundation Systems

San Francisco sits on a mix of sand, serpentine rock, and bay mud that shifts by neighborhood. A bid that says “standard foundation” without specifying the engineering, the rebar schedule, or the pier depth is not a bid. It’s a placeholder. The low bid often assumes a simple slab. The site might need helical piers, which cost five times more. Ask every bidder: “What foundation system did you price, and what happens if the geotech report requires something deeper?” If they can’t answer, they didn’t read the soil report.

Line Item 2: Exterior Cladding

Vinyl siding costs about $5 per square foot installed. James Hardie fiber cement runs $12 to $15. Cedar, stucco with proper waterproofing, or architectural panels cost more. A low bid often assumes the cheapest legal cladding. You want cladding that survives twenty years of San Francisco fog without warping. If one bid is dramatically lower, check the cladding line. You’ll usually find the answer there.

Line Item 3: Utility Connections

Connecting a new ADU to PG&E’s grid and SFPUC’s water and sewer lines can run anywhere from a few thousand dollars to $30,000 or more, depending on where your main lines sit and whether trenching crosses a public sidewalk. A low bid often budgets “TBD” or a placeholder of a few thousand dollars, then the real number arrives after demolition. Ask every contractor for a written utility line item with their best real range. If it says “contingency” or “allowance” with no number, you’ve found your overrun.

Line Item 4: Finishes and Fixtures

One bid prices a builder-grade bathroom: fiberglass tub, laminate vanity, stock tile. Another prices a cast-iron tub, custom vanity, and designer tile. You can’t compare those numbers head-to-head. The fix is to ask every contractor to price the same finish package: same tile, same faucet brands, same trim. Or, if you haven’t selected finishes yet, ask each bidder to list exactly what allowances they’ve included. “Allowance for bathroom finishes: $12 per square foot” tells you something. “Bathroom: $8,000” tells you nothing.

Before you pick the lowest bid, pull the four line items above from all three bids and compare them side by side. If the low bidder under-speced all four, they’re not cheaper. They’re quoting a smaller project than the one you described.

The Step-by-Step Hiring Process

Here’s the chronological process, from first search to signed contract, that we recommend to every San Francisco homeowner.

Step 1: Define Your Project Parameters (Week 1)

Before you call anyone, answer four questions. What’s the ADU for: rental income, a parent, a workspace? What’s your hard budget ceiling, the number you will not cross? What’s your timeline, and is it driven by a real date like a lease ending? And what’s your property reality: detached garage you can convert, open backyard, or a basement with ceiling height? The answers determine which contractor model fits.

Step 2: Run the CSLB Search and Build a Short List (Week 1)

Use the steps from earlier: license active, B classification, workers’ comp in place, no pattern of complaints. Build a list of 4 to 6 contractors. At Benson ADU San Francisco, our home addition team handles the full ADU process under the same roof, and we encourage every homeowner to compare us against other firms before signing.

Step 3: Run the 12-Question Script by Phone (Week 2)

Call each contractor on your list. Don’t email. A phone call tells you more in ten minutes than an email exchange tells you in two weeks. Ask the 12 questions from the script. Listen for the red flags. Cut anyone who fails two or more.

Step 4: Site Visits and Written Estimates (Weeks 2 to 4)

Invite your final three contractors to the property. They should measure, photograph, and ask about your goals. Afterward, each should deliver a written estimate with line items. Not a text message. Not a verbal number. A document you can save.

Step 5: Compare the Four Line Items (Week 4)

Pull the foundation, cladding, utility, and finish line items from each bid and compare them side by side. This is where you’ll see who actually read your property and who gave you a stock answer.

Step 6: Reference Calls (Week 5)

Call the references. Ask one question: “What was the gap between the original bid and the final price?” This is the honest number nobody volunteers. Then ask: “Would you hire them again for a second project?”

Step 7: Contract Review (Week 5)

Before signing, confirm the six contract elements from above are present: detailed scope, milestone-based payments, lien waiver schedule, change order procedure, 365-day warranty, and insurance certificates. If any are missing, ask for them in writing.

Step 8: Sign, Then Stay Involved (Week 6+)

Once the contract is signed, you aren’t done. The best homeowners stay mildly involved: a quick check-in each week, eyes on the payment milestones, and a standing rule that no change order happens without a written cost first. This is your project and your money. You paid for the right to ask questions.

Common Mistakes to Avoid

• Taking the lowest bid without checking the spec level. The low bid is rarely a gift. It’s usually a foundation assumption, a builder-grade finish package, and a utility cost that hasn’t been priced yet. Compare the four line items before you fall in love with a number.
• Skipping the CSLB workers’ comp check. A contractor without workers’ comp insurance is transferring injury liability directly to you. One injury on your property can turn a $200,000 ADU into a $700,000 lawsuit.
• Signing a contract with an “allowance” for anything bigger than a few thousand dollars. An allowance is a blank check. If the contract says “utility connection: allowance,” you’re agreeing to pay whatever the real number turns out to be, with no recourse.
• Hiring a contractor whose entire San Francisco portfolio is from before 2020. DBI processes have changed since then. You want someone who has pulled a permit in the current environment, not someone who remembers how it used to work.
• Paying by calendar date instead of milestone. A contract that says “$50,000 due May 15th” regardless of whether the foundation is poured is a contract that pays for work that hasn’t happened. Milestones exist for a reason.
• Ignoring the project manager mismatch. The person who sells you the job is almost never the person running it day to day. Meet the PM before you sign, and ask how many projects they’re currently carrying. A PM running eight simultaneous builds is not running yours.
• Assuming prefab is automatically faster. Prefab manufacturing is fast. San Francisco permitting and site work are not. A prefab ADU from Cover or Boxabl can sit waiting for DBI approval just as long as a site-built unit. Prefab helps with build speed, not permit speed.

The Bottom Line

Hiring an ADU contractor in San Francisco is a process of elimination, not selection. You eliminate the contractors with overloaded DBI queues, the ones who refuse to put their numbers in writing, the ones who quote a foundation without reading the geotech report, and the ones who can’t name their warranty terms. What’s left is a short list of professionals who treat your project like a legal and financial commitment, not a handshake. Whether you’re expanding a room or building a full ADU, the process is the same: verify, question, document, and never accept a verbal promise as a substitute for a written one. If you’re in San Francisco and ready to start, call (424) 328-5746 for a free estimate. We’ll put the price in writing before the first shovel turns.

Written by Troy Eastman, Owner at Benson ADU San Francisco, serving San Francisco since 2006.