Who is building California’s ADUs, and where they are

What Terner measured, and the gap this page is for

The Terner Center for Housing Innovation at UC Berkeley, with the Center for Community Innovation, owns the homeowner-facing evidence on California ADUs: who the owners are, what they paid, how they financed, who lives in the unit, how long coastal-zone permitting takes.

That work is cited here as Terner’s and CCI’s. It is not restated as ours.

Chapple, Ganetsos and Lopez, Implementing the Backyard Revolution (22 April 2021), surveyed California homeowners with 2018 or 2019 ADU permits or certificates of occupancy.

On page 35 they asked, “Who did the physical construction on your ADU?” (n = 674, select all that apply).

491 selected “a paid contractor”; 71 selected “multiple”; 48 selected “myself or another owner of the property.” A second chart on the same page (n = 664) asked whether the construction process was easy; the footnote is “This may include issues finding a contractor.” Those are owner reports about a completed job.

They are not a roster of firms, not a license table, and not a permit-volume map.

Reaching California’s ADU Potential (August 2020) and the later financing papers identified cost, products and underwriting as barriers. They did not publish a supply-side count of which CSLB classes hold the work, which counties the firms sit in, or how concentrated the named-contractor volume is in a given city.

HyreADU analysis: the missing object is the builder side. A homeowner who has decided to build still has to find a licensed contractor who has actually pulled an ADU permit in that city — and has no public way to tell a B that markets ADUs from a B that has been named on the permits.

This page maps the store we actually hold against the permit extracts we actually have. It will not invent the other 500 jurisdictions.

The board licenses dwellings. It does not license ADUs

CSLB’s Licensing Classifications page, retrieved 2026-09-05, lists the branches in Business and Professions Code § 7055: (A) General Engineering, (B) General Building, (B-2) Residential Remodeling, and (C) Specialty, then the C-2 through C-61 list.

There is no ADU, JADU, granny-flat or backyard-cottage classification. There is no ADU grade. The word does not appear on the list.

§ 7057 defines B. A general building contractor’s principal business is “any structure built, being built, or to be built, for the support, shelter, and enclosure of persons,” requiring at least two unrelated trades, “or to do or superintend the whole or any part thereof.” Framing or carpentry may be taken without that two-trade test.

Fire protection (C-16) and well drilling (C-57) may not be taken unless the B holds the specialty or subcontracts it. That is the statute that lets a B contract for a house. An ADU is a dwelling. The statute does not further qualify it.

B-2, added by SB 1189 (effective 1 January 2021), is residential remodeling of an existing wood-frame structure with at least three unrelated trades, and it is forbidden from structural changes to load-bearing portions. A detached new ADU is not a B-2 job on that text. The store holds zero B-2 classifications.

CSLB Fast Facts, “Tips for Building a Residential Accessory Dwelling Unit (ADU),” revision 11/2025, is the board speaking to consumers in terms.

Building an ADU “is considered a home improvement project under the Contractors State License Law.” A written Home Improvement Contract is required; the down payment cannot exceed $1,000. “B – General Building Contractors can build or install ADUs.” C-47 can install a manufactured unit built off site.

Other C-specialties “cannot generally manage a full ADU build or installation but can be subcontracted.” The leaflet states that CSLB licenses California’s 285,000 contractors.

Treating 735 store files as a share of 285,000 “ADU builders” would be a category error: 285,000 is every licensed contractor, and the store is the ADU-evidenced B subset of five cities.

HyreADU analysis: the Fast Facts sentence is the whole credential structure. The board will tell you which class may take the contract. It will not tell you who has taken one.

That determination lives at the building department, which is why the next sections are permit extracts and not a second pass over the license list.

What is actually on disk

The national-metrics file in this dataset still says total_companies: 0. It is stale. The count used here is a directory listing of data/adu-data/companies/ on 2026-09-05: 735 JSON files.

Companion listings: 737 license files (two companies hold a second license), 735 company-state rows (734 CA, 1 NM).

The New Mexico firm is Gibson Design Build, Las Cruces — in the store because it holds a California B and was named on a harvested permit, not because New Mexico is in scope. Store-based claims on this page are California claims.

Every one of the 735 files records adu_licence_class: null and a note that California licenses no ADU classification.

Every one holds B GENERAL BUILDING. 584 (79.5%) hold B and nothing else. 151 (20.5%) hold B plus at least one other class.

Classification-set sizes: 584 with one class, 94 with two, 38 with three, 13 with four, four with five, one with six, one with seven.

Years in business on these files are derived from the issue date of the earliest CSLB license.

They are the age of the license, not of the business; a reissue to a new legal entity resets them. Mean license age is 17.09 years.

Buckets: 9 at 0–2 years, 31 at 3–5, 204 at 6–10, 277 at 11–20, 214 at 21+. 491 of 735 (66.8%) have a license eleven years or older. This is not a cohort of new ADU specialists.

It is mostly general builders whose licenses predate the 2016–17 ADU bills, later named on an ADU permit.

Entity type on the 737 license files: 548 corporation (74.4%), 153 sole ownership, 30 limited liability, 6 partnership. All 737 are stored as primary_verified_active as of the 29–30 August 2026 CSLB harvest.

A live re-check of five license-detail URLs on 2026-09-05 was rejected by CSLB’s web application firewall; statuses on this page are the August harvest, not a 5 September census.

Lifecycle on the company files is not a quality grade. 560 sit at ELIGIBILITY_CHECK — the ceiling of a license-plus-permit pass. 175 sit at RANKING_READY because a reputation source (typically a BBB letter grade) was attached. RANKING_READY is an internal pipeline flag. It is not published here as a rank.

What else they hold, besides B

The additional classes are a picture of how ADU general contractors are otherwise ticketed, not a second ADU credential. C-10 Electrical (53 files) and C-36 Plumbing (41) are the trades a B would otherwise subcontract.

A General Engineering sits on 39 files. C-47 Manufactured Housing — the class Fast Facts names for a factory-built ADU — sits on three files. C-46 Solar sits on four.

A solar or electrical class on a firm that also holds B does not make the firm a specialist in ADU solar. It means the same legal entity is licensed for that trade.

Los Angeles’s third-highest named contractor by site count in the permit index is SOUTH COAST SOLAR (license 1025311, classes C46, B and C10 on the permit, CSLB status Expired as of 30 August 2026, 43 sites).

Los Angeles matching is a work-description sweep on “ACCESSORY DWELLING.” A solar install whose description names an existing accessory dwelling will match.

That is a limitation of the Los Angeles determination, not a finding that a solar contractor is an ADU builder. San Francisco and San José do not have this problem: those cities classify the permit themselves.

Additional CSLB classifications on the 735 company files, counted from disk 2026-09-05. Every file also holds B General Building. Classes with one or two files are omitted from the bars and remain in the source JSON.

A classification is the credential on the license, not a count of jobs in that trade. C-47 = 3 is the manufactured-housing class Fast Facts names for off-site ADUs; it is not a count of prefab ADUs built.

Where the firms sit, and why that is not where ADUs are built

Headquarters city is filled on every file: 158 distinct city strings. Headquarters county is not.

413 of 735 files (56.2%) have a null county. The nulls are concentrated in Los Angeles postal neighborhoods the CSLB record stores as a city and not as a county — Woodland Hills (34), Sherman Oaks (27), Tarzana (20), North Hollywood, Encino, Van Nuys, West Hills.

This page will not collapse those strings into Los Angeles County without a city-to-county crosswalk we did not run. City is the geography that covers the roster. County is reported only for the 322 files that have it.

Of those 322 filled counties: San Francisco 122, Los Angeles 115, Sacramento 34, Santa Clara 14, then Alameda and Ventura 8 each. Zero filled San Diego County rows. The city listing has no “San Diego” string; it has one San Ysidro. Orange County, a large ADU market on the HCD map, is three filled-county files.

That geography is an artifact of which building departments we could join to CSLB, not a map of California ADU construction.

The attached permit-track on the store — one jurisdiction per file, the one that qualified it — is 453 City of Los Angeles (61.6%), 181 San Francisco (24.6%), 66 Sacramento, 22 San José, 13 unincorporated Marin.

San Francisco is roughly a quarter of the store and 1.3% of statewide HCD ADU permits in 2018–2025. Los Angeles is 61.6% of the store and 27.8% of statewide HCD permits.

The store is over-weighted to the cities whose registers carry a contractor name we could match, and under-weighted to the rest of California, including San Diego.

Every store permit-track has two or more distinct site addresses: 380 files with exactly two, 218 with three or four, 100 with five to nine, 37 with ten or more, none with one.

The one-site majority in the permit index, shown below, was structurally excluded from the store. That is the floor, stated as a rule rather than as a finding about the market.

Headquarters city as stored on the company file, top ten of 158 distinct strings. Counted from disk 2026-09-05. Woodland Hills, Sherman Oaks, Tarzana and the other Valley strings are CSLB city fields, not a HyreADU assignment to Los Angeles County.

A headquarters is where the license sits, not a service area. A San Francisco B can pull a Marin permit; a Woodland Hills B can pull a Los Angeles permit. The permit-track, not the HQ city, is the determination.

Who the five cities actually named

The permit-contractor index, computed 2026-09-05 from harvests taken 29–30 August 2026, is the determination layer. It is 3,668 named-contractor records, 6,551 distinct site addresses, 6,623 kept building permits, declared valuation $769,106,274. Those are sums of per-jurisdiction records.

A firm named in Los Angeles and San Francisco is two records. They are not a unique statewide contractor count, and they are not a count of completed units.

Each city determines “this is an ADU permit” differently, and the difference is the method. San Francisco publishes an adu Y/N column; the city’s classification is the determination, restricted to issued permits.

San José classifies the permit subtype as “ADU Accessory Dwelling Unit.” Los Angeles, Sacramento and Marin are work-description matches, re-tested locally against a word-boundary pattern so that a bare “ADU” substring cannot hit GRADUATE, ADULT or MODULE.

Sacramento further drops trade activity codes so the electrician or plumber on an ADU job is not counted as the builder. Marin, with no permit-discipline field, drops solar/reroof/HVAC rows unless a builder verb also appears.

New single-family houses that contain an accessory unit are held out in every city — a production-homebuilder product, not the homeowner ADU these counts describe.

Los Angeles is the largest extract and the most incomplete. LADBS resource xnhu-aczu is the legacy building-permit file, last updated 22 May 2023. It is the only published Los Angeles shape that still carries the contractor of record and that contractor’s CSLB number.

Newer LADBS extracts dropped every contractor column. Contractor evidence in the City of Los Angeles therefore ends 19 May 2023. San Francisco’s last named permit in the harvest is 28 August 2026; San José’s is 27 August 2026; Sacramento’s is 24 July 2026; Marin’s is 20 July 2026.

Comparing a 2023 Los Angeles roster to a 2026 San Francisco roster as if they were the same year is a mistake this page will not make.

Owner-builder and missing-name rows are the other incompleteness. Los Angeles: 8,312 of 12,627 matching rows (65.8%) were coded owner-builder and excluded from contractor counts, plus 473 with no contractor. San Francisco: 671 of 2,005 (33.5%) owner-builder.

Sacramento publishes no owner-builder flag; 840 of 2,109 matching rows had no contractor name. San José: 825 of 1,291 (63.9%) had no contractor.

Marin: 37 owner-builder rows in the match, and 145 owner-builder permits still sitting in the harvest because that register does not always separate them cleanly. A missing name is not an owner-builder.

An owner-builder is not “the owner did the work.” Both are reasons the named-contractor count is a floor on the work.

A long tail, except where it is not

In four of the five cities, a majority of named contractors appear on one distinct site address: 68.1% in Los Angeles (1,359 of 1,995), 73.9% in San Francisco, 67.7% in Sacramento, 81.0% in San José, 86.4% in unincorporated Marin.

One-site firms account for a smaller share of sites than of contractors — 35.9% of Los Angeles named sites, 44.7% of San Francisco named sites — because the other tail of the distribution holds more addresses per firm.

The ten-plus club is small: 32 firms in Los Angeles, 11 in San Francisco, 9 in Sacramento, 1 in San José, 1 in Marin.

The top ten named contractors hold 8.8% of Los Angeles named sites and 10.6% of San Francisco’s. That is not a concentrated industry in those two cities.

It is a long tail of firms that have pulled one or two ADU jobs, which is what a B-plus-a-backyard-permit market looks like.

Sacramento is the exception. The top ten named contractors hold 28.0% of named sites in that extract — three times Los Angeles’s top-ten share. The highest site count in Sacramento is IMKAT CONSTRUCTION CORP, 56 sites, CSLB 1094866, current and active as of 30 August 2026.

San José’s top-ten share is 14.3%; Marin’s is 15.9%. Smaller registers, fewer names, a heavier head. A statewide “ADU builder industry” concentration number averaged across these five cities would be a fiction, and we do not compute one.

Share of named contractors who appear on exactly one distinct ADU site address, by harvested jurisdiction. Counted from the permit index, not from the 735-file store (the store excluded the one-site firms by rule).

One site is not one job in the sense of one building permit: siblings were collapsed to the address. It is still one property. A firm can have a long ADU career in a city this extract does not cover.

The demand the store cannot see

HCD’s Housing Element Annual Progress Report Table A2, retrieved 2026-09-05 from the data.ca.gov resource dated 2026-09-04T15:44:00Z, is the statewide production file. Filter UNIT_CAT = ADU; permits dated by BP_ISSUE_DT1 on unique events; completions dated by CO_ISSUE_DT1.

The method, including the double-count correction against a naive APR-year sum, lives in the permit-to-completion study. This page takes the statewide and focus-jurisdiction totals from that already-computed file and does not re-download Table A2.

178,495 ADU permits in California in 2018–2025, and 102,356 completions (cumulative ratio 57.3%). 511 jurisdictions reported at least one ADU permit in that window. 2025: 32,126 permits, 22,630 completions. ADUs were 26.1% of all HCD-reported housing permits in 2025, up from 9.1% in 2018.

The City of Los Angeles is 49,556 of those statewide permits (27.8%) and 29,529 completions. San José 3,337 permits / 2,104 completions. San Francisco 2,353 / 1,673. Sacramento 1,631 / 1,032.

Those four harvested cities together are 56,877 permits, 31.9% of the state. Unincorporated Marin is not a named focus row in the HCD file this desk computed; we do not invent a Marin HCD total from the county permit extract.

The City of San Diego, which is not one of the official five permit-index jurisdictions, is 9,153 HCD permits and 2,667 completions in 2018–2025 — more production than San José, San Francisco and Sacramento combined, with a completion ratio of 29.1%.

The store has essentially no San Diego headquarters. That is the harvest, not the market.

What a homeowner can actually do with this

Check the license at cslb.ca.gov, the way Fast Facts tells you to.

Confirm it is current and active, that the classification includes B (or C-47 for a manufactured unit), and that the number on the contract is the number on the board.

A canceled, revoked, expired or suspended license on a firm with a long permit history is still a canceled, revoked, expired or suspended license.

Ask for the city and the permit numbers of ADU jobs, not for a count of “ADUs built.” Then look those numbers up on the building department’s own register.

A firm that has pulled three ADUs in Sacramento has not, on that evidence, pulled three in San José.

The permit-contractor index is the public-record listing for the five cities this desk has; it is not a statewide directory and it is not a recommendation.

Get at least three bids on the same drawings, the way Fast Facts tells you to.

Compare them on completeness — same scope, site work as a line, utilities as a line, fees, named allowances, a draw schedule — not on a headline price.

The bid comparison is the worksheet. It will not rank the firms.

Do not treat a B that advertises ADUs as an ADU specialist. Do not treat a one-site permit as a track record. Do not treat a 2022 Los Angeles site count as a 2026 referral.

If the project only “works” because a website called someone the best ADU builder in California, it does not work on the evidence this page could source.

HyreADU analysis: the category has been answering a supply question with directories, because directories close a lead and public-record joins do not.

The honest picture in the five cities we can see is a long tail of B general contractors named on one or two ADU sites, a handful of higher-volume names whose licenses are not all current, a large owner-builder remainder in Los Angeles, and a statewide production file that is an order of magnitude larger than this roster.

We would rather publish that floor than a statewide builder map we cannot source.