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

Here’s a number most homeowners never hear: roughly seven out of ten ADU projects in San Francisco end up over budget, behind schedule, or tangled in a permit delay that could have been caught before the first check was written. The cause is rarely the build itself. It’s the hiring decision made in the first two weeks. This guide walks through the exact vetting process we’d use if we were hiring for our own backyard, starting with the one question that separates serious contractors from salespeople, and points to more guides & resources for homeowners navigating the ADU process. By the time you finish, you’ll know how to verify a license in under three minutes, which five documents to demand before signing, and how to structure the relationship so you’re never left wondering what’s happening on your own property in San Francisco.

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Quick Answer

To hire an ADU contractor in San Francisco, first verify the license on the CSLB website, then request a written fixed price before any permit is filed, and review a contract that includes scope, timeline, lien releases, and a written guarantee. A legitimate contractor will put all of this in writing without hesitation. A contractor who resists any of these steps is telling you exactly who they are before you hand over a deposit.

Table of Contents

• The One Question That Predicts Everything
• Step 1: Verify the California Contractor License in Under Three Minutes
• Step 2: The Five Documents to Request Before You Sign Anything
• Step 3: What a Legitimate San Francisco ADU Contract Must Include
• Step 4: Why the Lowest Bid Is Usually the Most Expensive
• Step 5: Structuring Communication So You’re Never Left Waiting
• Step 6: San Francisco-Specific ADU Requirements That Change the Math

The One Question That Predicts Everything

Before you ask about timelines, materials, or references, ask this: “Will you give me a written fixed price before the permit is filed?”

Most contractors won’t. They’ll explain that San Francisco permits are unpredictable, that city fees shift, that they need to see what’s behind the walls first. Some of that is true. But a contractor who knows ADU work in San Francisco can account for the known unknowns in writing. A contractor who refuses is signaling that the risk is yours, not theirs, and that your project will be priced on a cost-plus basis that can climb month after month.

At Lodgewick ADU San Francisco, the written price comes before any work starts, every time. That price is fixed and documented. If something changes in the field, the change gets agreed to in writing before work proceeds. There’s no door-price surprise. In our experience across San Francisco, from Sunset District garage conversions to Bernal Heights backyard cottages, the contractors who quote honestly up front are the same ones who finish on schedule.

Step 1: Verify the California Contractor License in Under Three Minutes

Every home service business in San Francisco that performs work over $500 must hold a valid California Contractors State License Board (CSLB) license. The search takes less time than ordering a cup of coffee, and it’s the first filter that eliminates a meaningful share of bad actors.

1. Go to the CSLB website and click “Check a License.”
2. Search by company name or individual name. If you have a license number, even better – enter it directly.
3. Confirm the license status says “Active.” Anything else – expired, suspended, revoked – means walk away immediately.
4. Check the classification. For ADU construction, you want a Class B (General Building Contractor) or a Class A (General Engineering Contractor) if the project involves significant grading or retaining work. A Class C specialty license only covers one trade, like plumbing or electrical.
5. Verify the business name on the license matches the name on the contract. If they don’t match, ask why.
6. Scroll to the bottom for any enforcement actions, citations, or license suspensions in the past five years.

For ADU work specifically, the difference between a Class B and a Class C license matters. A general contractor with a Class B can supervise and schedule every trade: framing, electrical, plumbing, roofing, and finish work. A specialty contractor cannot legally pull permits for the whole project. That’s why the classification check takes an extra 30 seconds and saves you from hiring someone who can’t legally do the job they quoted.

What a Red Flag Response Looks Like

If a contractor resists giving you their license number, says it’s “in the truck” or “at the office,” or gives you a number that doesn’t match any CSLB record, the interview is over. No exceptions. A licensed contractor is proud of that credential and will hand it over before you ask. In San Francisco, the city also requires a Business Registration Certificate, which is separate from the state license. A contractor doing ADU work in the city should be able to show both.

Step 2: The Five Documents to Request Before You Sign Anything

You don’t need to be a construction expert to protect yourself. You need to request the right paperwork and watch how they respond. This step alone filters out most of the contractors who intend to take a deposit and underdeliver.

Document 1: Written Fixed-Price Proposal with Line Item Detail

The proposal should break down costs by category: site work, foundation, framing, electrical, plumbing, insulation, drywall, finishes, and a contingency line. If the proposal is one number with no explanation, that’s a red flag. A one-page lump sum tells you nothing about what happens if a line item runs over. A detailed proposal tells you where your money goes and gives you a basis for holding them accountable later.

Red flag response: “We’ll figure out the details after we start.”

Document 2: Certificate of Insurance with Named Insured Matching the Contractor’s Legal Name

Ask for a certificate of general liability insurance with limits of at least $1 million. The named insured should exactly match the name on the license and the contract. If they’re carrying a policy under a different company name, the coverage may not apply to your project. You can also request to be added as an “additional insured,” which most legitimate contractors will do without complaint.

Red flag response: “Our insurance covers everything, you don’t need to see it.”

Document 3: Written Guarantee with Duration and Scope in Plain English

The guarantee should state, in writing, what is covered, for how long, and what happens if something fails. Here’s what ours says at Lodgewick ADU San Francisco: if the work isn’t right within the 365-day guarantee period, we come back and make it right, free of charge. That’s the 365-Day Done Right Promise, and it’s part of The Kingswell Guarantee – written price first, real arrival window, clean job site, and written guarantee on every project. A contractor who won’t put a guarantee in writing is telling you they don’t plan to be reachable after the final check clears.

Red flag response: “Don’t worry, we stand behind our work.” But nothing in writing.

Document 4: Lien Release Schedule Tied to Payment Milestones

If the contractor doesn’t pay their subcontractors or suppliers, those parties can file a mechanic’s lien against your property – even if you paid the contractor in full. A lien release schedule protects you. Every time you make a payment, you receive a signed release from every subcontractor and supplier who worked up to that point. This should be structured into the contract before signing, not added later.

Red flag response: “We handle all the subs, you don’t need to worry about them.”

Document 5: Written Project Timeline with Specific Milestones

A legitimate ADU build in San Francisco takes five to eight months from design to certificate of occupancy, depending on scope and permit speed, which is why understanding Seasonal ADU Care for San Francisco: Year-Round Homeowner’s Guide can help you time your project wisely. The timeline should break the project into phases: design, permit submission, permit approval, site work, foundation, rough framing, MEP (mechanical, electrical, plumbing), insulation and drywall, finishes, final inspection. Each phase gets a start and end date. If a contractor wants to start work without a written timeline, they’re asking you to fund an open-ended project.

Red flag response: “It’ll be done when it’s done.”

For a deeper look at how a full project should be structured, see our Home Addition Contractor in San Francisco guide, which covers the same document standards for larger builds.

Step 3: What a Legitimate San Francisco ADU Contract Must Include

A contract is not a formality. It’s the single document that determines whether you have recourse when something goes wrong. In San Francisco, where ADU permits involve city-specific requirements that can add weeks to a timeline, a vague contract is a license for scope creep.

Here’s what every ADU contract in San Francisco must include, in plain English:

• Scope of work. A complete description of what is being built: square footage, number of rooms, finishes, appliance specifications, exterior materials. If it’s not written in the scope, it’s not included in the price.
• Written fixed price. The total contract price, broken down by line item, with a stated contingency that does not exceed a specific percentage (in our work, that’s typically 5-10% for unforeseen site conditions, and any unused contingency is returned to the homeowner).
• Timeline with milestones. Start date, completion date, and the dates by which each phase will be completed. Include a defined arrival window for crews so you’re never waiting on a truck that never shows.
• Permit responsibility. Who pulls the permits, who pays the permit fees, and what happens if the city requires changes during plan review. In San Francisco, the Department of Building Inspection processes ADU permits, and a contractor who knows the city’s rules can move this step faster than one who’s learning on the job.
• Lien release schedule. Payment milestones tied to specific deliverables, with signed lien releases from all subcontractors and suppliers before the next payment is released.
• Guarantee terms. The duration of the workmanship guarantee, what it covers, and the specific process for requesting a return visit if something fails. Ours is the 365-Day Done Right Promise: if the work isn’t done right during that first year, we come back and make it right, no charge.
• Change order process. How changes get requested, priced, and approved in writing before work proceeds. No verbal changes. Ever.

In our experience building ADUs across San Francisco, the contractors who resist written change-order processes are the same ones who end up presenting a surprise invoice at the end of the project. The Kingswell Way is simple: say the price before the work, show up in the window given, leave the place cleaner than found, put the guarantee in writing, come back if it fails. A written contract is the vehicle for all of that.

Step 4: Why the Lowest Bid Is Usually the Most Expensive

The instinct is natural: get three bids, pick the lowest, save money. In San Francisco ADU construction, that instinct routinely produces the most expensive outcome. Here’s the math.

Say you get three bids for a 750-square-foot detached ADU with one bedroom and one bathroom. Bid A comes in at $310,000. Bid B at $340,000. Bid C at $368,000. Bid A is the obvious choice until you look at what’s missing: no contingency line, a scope that specifies “framing and finish to match existing” without naming materials, no allowance for the soil conditions on your specific San Francisco lot, and no written timeline.

Six months later, here’s the scope creep: foundation added $18,000 when the soil required deeper footings. Electrical upgrade added $9,000 because the existing panel wasn’t specified. The “finish to match” clause meant a lower grade of flooring and countertops than the other bids quoted, so you paid another $14,000 to upgrade. Written change orders totaled $41,000. Your “cheapest” bid cost $351,000, and the project ran three months over because the contractor was juggling other jobs to stay solvent.

Meanwhile, the higher bids included those items from the start. The $368,000 bid might have been the least expensive on day one, because the price was complete.

The lesson: a written fixed price with line-item detail is worth more than a lower number with a vague scope. The Kingswell Guarantee exists because we’ve seen this pattern repeat across the city. Written price first, always. If a contractor can’t tell you exactly what’s included for that number, they can’t be held to it.

Step 5: Structuring Communication So You’re Never Left Waiting

Most homeowner frustration isn’t about the work. It’s about the silence. A project goes quiet. Texts go unanswered. Phone calls hit voicemail. Days pass. The homeowner starts to worry, then to rage, then to regret. This pattern is entirely preventable, but only if you set the expectation before the contract is signed.

Here’s the structure we recommend, and the one we follow:

1. Written communication protocol in the contract. Specify how updates will be delivered (text, email, project portal), how often (at minimum once per week on active build days), and when you can expect a response to any question. Our standard at Lodgewick ADU San Francisco is a same-day response, and a live person answers calls 24 hours a day, 7 days a week – not a voicemail, not a chatbot.
2. Weekly progress report. Every Friday, you receive a written update: what was completed this week, what’s scheduled for next week, any changes to timeline or price, and a photo or two of the site. This takes ten minutes to write and eliminates ninety percent of homeowner anxiety.
3. Defined escalation path. Who do you contact if something feels wrong? The project manager? The owner? Both? Write it down. At Lodgewick, you can reach Russ Delmar directly with any issue on your project.
4. Site visit schedule. You should be able to walk the site with the contractor at pre-scheduled intervals: after foundation, after rough framing, after mechanical systems, at final walkthrough. If a contractor discourages site visits, that’s a red flag.
5. A 24-hour response guarantee in writing. If you ask a question by text or email, you get an answer within 24 hours. Not “soon.” Not “when we get a chance.” Within one business day. If a contractor can’t commit to that, ask yourself how they’ll handle a real problem.

Our crews are background-checked and uniformed, so you always know who’s on your property. That’s part of The Kingswell Way, and it’s in writing on every project. No surprises at the door, no strangers in the backyard, no silence when you ask a question.

Step 6: San Francisco-Specific ADU Requirements That Change the Math

San Francisco is not like building an ADU in Sacramento or San Jose. The city has its own set of rules, fees, and neighborhood conditions that affect cost, timeline, and design. A contractor who’s never built in San Francisco will learn these lessons on your dime.

Zoning Differences by Neighborhood

San Francisco’s zoning map is a patchwork. A detached ADU in the Sunset District faces different setback, height, and floor area ratio requirements than one in the Richmond, Bernal Heights, or the Mission. Some areas have historic district overlays that add design review and months to the process. Your contractor should be able to tell you, by address, what district you’re in and how it affects your project before you pay for a survey.

Soft-Story and Seismic Requirements

San Francisco sits on some of the most dynamic soil in the country, and the city’s seismic requirements are stricter than nearly anywhere else in California. A garage conversion ADU in a soft-story building triggers additional engineering, which can add $15,000 to $40,000 depending on the existing structure. A contractor who doesn’t mention this in the first conversation hasn’t built enough in San Francisco to know what they’re up against. For garage conversions specifically, see our Garage Conversion Contractor in San Francisco page for a breakdown of what’s involved.

Prefab vs. Stick-Built: What Works on San Francisco Lots

San Francisco lots are famously narrow and difficult to access, which makes modular and prefab ADUs increasingly popular. We work with established prefab manufacturers including Mighty Buildings and Boxabl, and we’ve matched their systems to tight city lots where traditional stick-built delivery would be impossible. A prefab ADU can cut build time significantly, but the site work – foundation, utilities, accessibility for the delivery – remains site-specific and San Francisco-specific. If your lot is on a steep hill with limited street access, that changes which manufacturers make sense. Our team has worked with materials from ADU Builders in San Francisco using systems that fit San Francisco’s unique site constraints.

Permit Timelines and Fees

San Francisco’s Department of Building Inspection has improved ADU permit processing in recent years, but plan review still takes longer than many surrounding cities. Expect permit fees for a typical ADU to run between $8,000 and $20,000 depending on scope, and plan for two to five months in the permitting pipeline. A contractor who promises “permits in six weeks” is either new to the city or comfortable overpromising. The right contractor tells you the realistic range and helps you plan around it.

Common Mistakes to Avoid

• Paying a large deposit before anything is in writing. In California, the legal limit for a down payment is $1,000 or 10% of the contract price, whichever is less. Any contractor asking for more is violating state law. In San Francisco, where the average project is $300,000+, a contractor asking for 50% up front is a walking red flag.
• Signing a contract with a vague scope. “Garage conversion, 400 square feet, finishes to match existing” tells you nothing. A scope should name materials, fixtures, and appliances, or state explicitly what is not included.
• Choosing a contractor with no written guarantee. If the guarantee isn’t in writing, it doesn’t exist. The 365-Day Done Right Promise at Lodgewick ADU San Francisco is written on every project before work begins – not a verbal assurance, a commitment on paper.
• Skipping the CSLB license check because the contractor “seemed nice.” Nice is not a credential. The license check takes three minutes and is the single most effective vetting step you can take.
• Allowing verbal change orders. “Let’s bump the ceiling height a few inches” is how a $320,000 bid becomes a $360,000 invoice. Every change gets priced and approved in writing before work proceeds.
• Not assigning someone to manage the project. A contractor juggling three jobs in San Francisco will prioritize the project with a client who communicates clearly and holds them accountable. The weekly progress report structure prevents this.
• Hiring based on the first bid you receive. You need at least three, and you need to compare line items, not just totals. The lowest bid usually has the most missing items.

When to Call a Professional

Some things are worth doing yourself. Permitting an ADU in San Francisco is not one of them. If your project involves structural changes to an existing building, new foundation work, electrical panel upgrades, gas line extension, or a soft-story retrofit, you need a licensed contractor and, in many cases, a structural engineer. Attempting to coordinate these trades independently is how projects stall for a year and cost double their original estimate. The city’s permit process alone requires drawings, calculations, and iteration that professionals handle as a matter of routine. If you’re uncertain where your project falls, call a contractor and ask. Lodgewick ADU San Francisco offers free estimates in San Francisco – call (707) 760-0502 and we’ll walk through your lot, your goals, and what’s feasible before any money changes hands.

The Bottom Line

Hiring an ADU contractor in San Francisco is a multi-month financial relationship that touches your property, your permits, and your neighbors. The vetting process should match that weight. Verify the license on the CSLB website. Request five documents before signing. Demand a contract with written scope, fixed price, timeline, lien releases, and a written guarantee. Reject anyone who can’t provide all of it. In San Francisco, where the cost of a mistake can run into six figures, the contractor who puts everything in writing is the one worth hiring. The Kingswell Guarantee exists for exactly this reason: written price first, real arrival window, clean job site, written guarantee on every project, and a live person on the phone when you call.

Written by Russ Delmar, Owner at Lodgewick ADU San Francisco, serving San Francisco since 2010.