ADU Builders in San Francisco: How to Choose and Check One

The market, from the record

What ADU work in San Francisco actually looks like

Before choosing a builder, know what the job is. We read every ADU-flagged permit filed in the city since January 2023 — 469 of them — and set aside the 155 that bundle an ADU with a larger remodel. That leaves 314 standalone ADU projects.

Seven in ten San Francisco ADUs with a known type are conversions. That is a different trade from building a backyard cottage. It means working under an occupied building: structure, fire separation, ceiling height, light, exits, and often neighbours or tenants upstairs.

So the first filter is simple. Ask a builder how many conversions they have finished in San Francisco — not how many ADUs they have built in the Bay Area. A firm with fifty detached units in the suburbs has not necessarily done one of these.

Where the permits are

Of the 469 permits, the supervisorial districts with the most were District 8 (76), District 11 (59), District 4 (55), District 9 (54) and District 2 (51). That takes in Noe Valley and the Castro, the Excelsior and Outer Mission, the Sunset, the Mission and Bernal Heights, and the Marina and Pacific Heights. Housing types differ sharply between them, so a builder's experience in your kind of building matters more than their experience in the city at large. Our neighbourhood guide to the west side: Sunset District ADUs.

The eight questions

Eight questions a San Francisco ADU builder should answer without hesitating

A builder does not need to be a lawyer. But in this city the builder and designer are usually the first professionals an owner talks to — and an owner who is not warned about these points finds out after the drawings are paid for.

1. "Would you file this under the Local Programme or the State Programme — and why?"

San Francisco has two routes: the Local Programme (Planning Code §207.1) and the State Mandated Programme (§207.2). They carry different standards. A builder who does not know there are two has not permitted an ADU here.

2. "What does that choice do to rent control?"

A new ADU is subject to the San Francisco Rent Ordinance if it is built under the Local Programme, if it is added to a building that already has a rent-controlled unit, or if the owner requested a waiver. Such units are registered under a recorded agreement. This is the most consequential decision on the project and it is made on the application form. Our guide: Will my SF ADU be rent controlled?

3. "Does my design need a waiver — and is that waiver available?"

Under the Local Programme, waivers exist for density, open space, rear yard and exposure. They are never available for ceiling height, ventilation, fire safety or exits. A builder who says "we'll get a variance for the ceiling" is describing something the programme does not offer.

4. "There are tenants in the building. Can we use the garage?"

A good builder stops here and tells you to call a lawyer. A tenant's garage, parking space, laundry, storage, deck or garden can be a housing service under the Rent Ordinance. Legal analysis of the 2025 amendments reports that removing one without just cause exposes the owner to treble damages and attorney's fees — and that building an ADU is not just cause.

5. "Will my lower level qualify?"

For a basement or ground-floor unit the gates are ceiling height, light and air, a way out, structure and fire protection. Ask how the builder would establish each one for your building before you pay for full drawings — and who measures. Our guide: SF basement to ADU.

6. "I may want to sell the ADU separately one day. What do I need to do now?"

San Francisco has opted in to separate sale of ADUs as condominiums, but the tests are strict: the ADU must be built under the State Programme only, on an application submitted on or after May 1, 2025, on a lot with four dwelling units or fewer, and junior ADUs are excluded. A unit filed under the wrong programme cannot be fixed later. Our guide: Sell an SF ADU separately.

7. "Could I fit two detached ADUs from 2027?"

From January 1, 2027, state law allows two detached new-construction ADUs of up to 800 sq ft each on a single-family lot. It is realistic mainly on deeper, wider or corner lots, and nobody should promise it fits a standard 25-foot San Francisco lot. A builder who promises two units before measuring is selling. Our guide: Two detached ADUs in San Francisco from 2027.

8. "How long did your last three San Francisco ADU permits take?"

Ask for the permit numbers. The city's permit tracker is public, and you can read the filing and issue dates yourself. For context: the median across 194 standalone ADU permits was 216 days from filing to issuance, and one in four took more than a year. A builder whose answer is "about two months" is quoting the statute, not their record. The full breakdown: How long an ADU permit takes in San Francisco.

The licence

Check the licence before the second conversation

Every contractor who builds an ADU in California needs an active licence from the Contractors State License Board. Look it up at cslb.ca.gov by number or business name.

• Status: active, not expired or suspended.
• Name: the same legal name that will be on your contract.
• Classification: one that covers building a dwelling, not a single trade.
• Workers' compensation: a policy on file — or an exemption, which means the contractor has declared no employees.
• Bond and disclosed complaints: shown on the same record.

Then check the experience claim the same way. Take the permit numbers the builder gives you, look each one up in the city's permit tracker, and confirm the contractor named on the permit is the one in front of you.

The bid

Make the bids comparable — especially here

A conversion bid depends on what is behind the walls of a building nobody has opened yet. Three habits keep you out of trouble:

1. One written scope for every builder. Same unit, same size, same finish level.
2. Ask what was assumed about the existing building. Foundation adequate? Ceiling height as measured? Existing sewer and electrical service sufficient? Each assumption is a possible change order.
3. Separate the lines. Construction; design and engineering; fees; utilities and site work; allowances and exclusions; schedule; payments tied to completed work.

Our 13-line quote comparison worksheet sets this out so you can print it and fill in a column per builder.

A note on price. We publish no city-wide cost range for San Francisco ADUs, because we do not have a sourced one. Permit records carry a declared valuation, but a declared valuation is the figure written on a permit form — it is not what the project cost — and we do not present it as a price. The one planning range we do publish for the city is on the basement conversion page, with its source.

Design-build or separate firms

Who draws it, who builds it

You will meet three arrangements in San Francisco:

• Design-build firm. One contract covers drawings, permits and construction. Fewer hand-offs; you rely on one company's judgement for both design and price.
• Architect or designer, then a general contractor. You own the drawings and can bid them to several builders. More comparable bids; more coordination falls to you.
• Permit expediter or ADU consultant plus a contractor. You will meet this on conversions too. Check exactly who is responsible for the programme choice and the application.

None is the right answer for everyone. What matters is that someone specific is accountable for the eight questions above, in writing, before you sign.

Ready to start

If you plan to hire in the next 90 days

Builders give their best attention to owners who arrive ready. Have this on one page:

• The address, the number of existing units, and whether any is tenant-occupied.
• The space you want to convert or the yard you want to build in, with rough dimensions and ceiling height.
• What the unit is for: family, long-term rental, or future sale. Each points to a different programme.
• Your budget range and how it is funded.
• Your timing: when you want to file.

The lot checker below asks these questions and puts the answers into a brief you can hand to any builder.

Questions, answered

San Francisco ADU builders: quick answers

Keep going

Related San Francisco guides

Check your lot

Build the brief a builder can price

Type your address and tap twice. You get a plain-language verdict on screen — what your lot can likely take and the questions to settle first — before we ask for any contact details. If you choose to save your brief, we store it and tell you so. No builders are signed to our roster yet, so no quotes are available today and no builder will contact you.