Research

HyreADU research

Original analysis of California accessory dwelling units, computed from municipal permit records, HCD production returns, HUD rents and the statute — not from builder marketing.

Updated September 2026 · Data as of Municipal permit extracts through 2026-08-29; sources re-retrieved September 2026

Written by HyreADU Research Desk Primary-source research and data analysis

CA the only state this desk makes store-based claims about 734 of 735 companies; 1 New Mexico

5 jurisdictions with extracted ADU permit evidence Los Angeles, San Francisco, Sacramento, San José, unincorporated Marin

735 CSLB-verified companies in the store A floor, not a census of every ADU builder

What this is

We publish original analysis of California ADUs from primary sources: municipal building-permit open data in five named jurisdictions, HCD’s Annual Progress Report, HUD Fair Market Rents, Census ACS housing tables, the California Contractors State License Board, and the state ADU statute.

Every study names its source files, publishes its method, and states its geography in the first screen.

This is a California program. Figures from our company store are titled to California, and where permit evidence exists it is titled to Los Angeles, San Francisco, Sacramento, San José and unincorporated Marin — never to the United States.

Research is attributed to the HyreADU Research Desk, never to an individual. Nothing on these pages is legal, tax or financial advice, and HyreADU does not design, permit or build ADUs.

What this desk will not do

The desk will not rank builders. California licenses no ADU classification and no ADU grade.

A B General Building license evidences that a firm may contract for a dwelling, not that it builds ADUs well, or at all.

Where we publish contractor names they come with a public-record permit count in a named city, a retrieval date, and no score.

It will not treat permits as production. HCD’s Annual Progress Report carries both permits issued and units completed. Almost every published ADU figure quotes the first as if it were the second. The studies below keep them apart.

It will not restate Terner Center research as ours. The Terner Center for Housing Innovation at UC Berkeley owns much of the homeowner-facing ADU evidence in California. We cite it, we complement it on the supply side and on the permit-versus-completion cut, and we never put their finding in our voice.

It will not give legal advice. The ADU provisions were recodified out of Government Code §65852.2. Every citation of the statute on this site is checked against the current numbering before it ships, and a zoning page that cannot name the ordinance does not ship.

What it costs

What an ADU costs to build, what the city charges on top, and why the fee line is the least predictable part of the budget.

750 sq ft Database · Cost and fees What an ADU costs in fees — and the cliff at 750 square feet The rules are unambiguous and fully sourced. The schedules that put numbers on them are, as far as a machine can reach, unpublished. Read the study $100k–$178k Research · Cost and fees What an ADU actually costs to build in California A range, and what moves you along it. Bid, survey average, declared permit valuation and a blog $/sf are four different numbers. This page keeps them apart. Read the study 750 sq ft Research · Cost and fees Utility connections: the constraint nobody budgets for Four different charges get called "the connection fee". State law waives one of them, caps a second, leaves the third alone, and says nothing at all about the fourth. Read the study $120/sf Research · Cost and fees What builders tell the city an ADU is worth — and why it is not the cost Declared permit valuation is the single most available ADU cost number in California, and the single most misleading. This page measures how wrong it is, and in which direction. Read the study

Permits and what gets built

How many are permitted, how many are finished, how long each stage takes, and where the published data stops being reliable.

162 days Research · Permits and production How long does an ADU take to approve? Medians and interquartile ranges from the cities that publish both an application date and an issued date. The 60-day statute is a different clock, and we do not pretend otherwise. Read the study 499 days Research · Permits and production From permit to final inspection: how long an ADU really takes Every published ADU timeline is a builder describing their own construction phase. This one is measured from the City of Los Angeles permit record, Read the study 57.3% Research · Permits and production California permits thousands of ADUs. How many get built? Permits are not production. A reconstruction of HCD’s Housing Element Annual Progress Report, Table A2, 2018–2025. Read the study 26.1% Research · Annual The California ADU annual report — the 2025 reporting year One permanent URL, republished each spring when HCD releases the Annual Progress Report. This edition covers reporting year 2025, retrieved 5 September 2026. Read the study 920 sq ft Research · Permits and production How big are the ADUs people actually build? The rule picks the number Every competitor page says “typically 600 to 800 square feet” and none of them says where that came from. Here is the measured distribution, and the two statutory lines it is piled against. Read the study 52.1% Research · Permits and production ADU production against housing need, jurisdiction by jurisdiction Californian cities are assigned a housing need every eight years. This measures how much of what they are actually permitting is accessory dwelling units — Read the study 53.8% Research · Permits and production Where ADUs are actually being built — and how concentrated that is The equity question was answered by Terner and the Center for Community Innovation, and we credit them for it rather than restating it as ours. What we add is a current, maintained, Read the study 34–80% Research · Permits and production How many unpermitted ADUs are there? What the record actually supports A unit built without a permit is, by construction, missing from the dataset that would count it. This page publishes what the prior research really found, on which denominators, and where it has been misquoted. Read the study 1,205 Database · Research infrastructure Where California cities publish their permit data — and what state it is in A portal is not a dataset. We ran the queries, recorded the last record in each store, and published the ones that publish nothing. Read the study

Zoning and the ordinance

What the state floor guarantees, what a city may still require, and what the ordinances actually say once you read them.

No ordinance Database · Zoning and ordinance Every California city’s ADU rules — the schema, the floor, and what we have actually read The normalisation is the hard part, so we publish the schema. The state floor is the baseline every row is measured against, so we publish that in full. And we publish the wall we hit. Read the study 1 Jan 2020 Research · Zoning and ordinance Legalizing an unpermitted ADU — the amnesty programs, and their expiry dates The state route is stronger than most owners think, the local programs have deadlines, and at least one city is publishing a repealed section number as its legal basis. Read the study 1 space Research · Zoning and ordinance ADU parking and the half-mile transit rule The maximum is one space whatever the bedroom count, six separate conditions reduce it to zero, and the widest of them turns on how the statute defines a bus stop. Read the study Prohibited Research · Zoning and ordinance Owner-occupancy rules: what your city’s code still says The single provision most likely to turn an investor’s answer from yes to no — and the one where the printed municipal code is most likely to be out of date. Read the study Null and void Research · Zoning and ordinance How California enforces its ADU law against cities — and what we could not retrieve We set out to compile every HCD letter of findings against a non-compliant ADU ordinance. HCD’s website was unreachable for two consecutive sessions. This is the honest page: the machinery, Read the study ~90% Research · Zoning and ordinance Building an ADU in the coastal zone One per cent of California, some of its most valuable land, and the one place where the ADU statute explicitly does not override the local process. Read the study Not required Research · Zoning and ordinance SB 9 lot splits and how they interact with ADU rights Two routes to more units on one parcel. Use both and the statute stops guaranteeing you the ADU — and, separately, there are now two different bills called SB 9 in this area. Read the study

Beyond California

What the federal datasets can and cannot count, and which other states have legalized ADUs in their own session laws.

6 of 6 Database · National and state law Which states have actually legalized ADUs Having a law and having a law that produces buildings are different things. We score on the six provisions that decide which one you have. Read the study 1 Research · National and state law ADU growth outside California: do the new laws work? A statutory right is not a housing unit. This page tests the gap — and finds that the main obstacle to testing it is that hardly any state counts. Read the study No count Research · National and state law How many ADUs are there in America? The honest answer Nobody knows. That is not a dodge — it is a finding with a mechanism, and this page publishes the mechanism, the closest defensible estimate, and the error bars that estimate’s own authors printed. Read the study 7 of 7 Research · National and state law Who actually adopted the model ADU ordinance? Model codes are supposed to propagate. This page tests whether they do — and is explicit about the comparison we set out to run, could not run, and refused to fabricate. Read the study 4 Research · National and state law Why the national permit data cannot see ADUs Not “has not counted them yet.” The Census Building Permits Survey is structurally incapable of producing an ADU number, in two separate ways, and this page shows you the instrument. Read the study

Code, utilities and hazard

Fire, flood, wildfire, septic, solar and the electrical service — what the code requires and who is licensed to do it.

No Research · Codes and hazards Sprinklers, fire separation and the wildland interface One of these three questions has a clean statutory answer that is routinely got wrong at the counter. The other two do not, and we would rather show you the gap than fill it with something we did not read. Read the study 140 A Research · Codes and hazards Does an ADU need a service upgrade? The honest answer is that a web page cannot tell you. What a page can do is name the four inputs that decide it — and flag the one that has quietly inverted since 2023. Read the study The county Research · Codes and hazards Building an ADU on septic Three regulators, one decision, and it is not made by any of the first two. Plus a straightforward admission: nobody can tell you how many California homes are on septic, including us. Read the study 7 of 16 Research · Codes and hazards Does an ADU have to have solar? Two tests, applied in order. Most ADUs fail the first one and never reach the second — and a surprising number of the ones that do reach it are exempt anyway, by arithmetic. Read the study Preempted Research · Codes and hazards The cities where your ADU cannot have gas A question with a clean answer in 2022 and a genuinely unsettled one now. We report the mechanism and the ruling, and we do not publish a city list we could not verify. Read the study 0 Research · Codes and hazards ADUs as rebuild housing after wildfire The state records every damaged structure over 120 square feet. It has no category for an accessory dwelling unit — so nobody knows how many burned, including the state. Read the study 50% Research · Codes and hazards Building an ADU in a flood zone The permission is rarely the problem. The elevation is, and the 50 per cent rule is — and the 50 per cent rule punishes exactly the cheapest way to build an ADU. Read the study

Renting it out

Rent control, short-term rental limits, the minimum term the statute now mandates, and who is allowed to live there.

51% Research · Tenancy and rental ADUs as rental housing: what the rents actually look like HUD Fair Market Rent and ACS gross rent by California market, set against a survey in which a substantial share of ADUs are occupied by family at below-market rent or none. Read the study 15 years Research · Tenancy and rental Is a new ADU exempt from rent control? Two statutes, two clocks One exemption is permanent, one expires, and the one most landlords reach for is the one an ADU probably cannot use. Read the study Shall Research · Tenancy and rental Can you short-term rent an ADU? The rule stopped being optional The permission a city used to have is now an obligation it carries. Most published guidance on this question is describing the law as it stood before 1 January 2026. Read the study 51% / 16% Research · Tenancy and rental Who lives in ADUs? The evidence, and its expiry date A synthesis of the Center for Community Innovation’s statewide owner survey, cited as theirs, joined to where California is permitting units now. The join is ours. The occupancy findings are not. Read the study

Money and value

What lenders will count, what appraisers can evidence, what the assessor adds, and the value figure nobody can source.

No national % Research · Financing and value Do ADUs add value? The appraisal evidence, the GSE rules, and the county assessor — four numbers that are not the same, and a widely circulated percentage that cannot be traced. Read the study 62% Research · Financing and value ADU financing: why the money is the hard part The products actually on the market, and the underwriting rule that still will not count rent from a unit that does not yet exist. Read the study 0 of 5 Research · Financing and value What an ADU does to your property tax bill — and what no assessor will tell you The statute is clear and the county guidance is missing. Both of those are findings, and the second one is the reason this page exists. Read the study 0 Research · Financing and value The CalHFA ADU grant: what we could not find out A public subsidy program whose award-level record we could not obtain from any state source on the retrieval date. This is a research note about that, not an analysis we do not have the data to write. Read the study 5 Research · Financing and value Insuring an ADU: what changes when you add a second unit The statutory architecture is retrievable and useful. The California market data is not, and this page says so instead of substituting broker commentary for evidence. Read the study

Who builds them

Who is named on the permits, how long those firms last, and what the license register does and does not publish.

5 Database · Builders and supply Who is named on California’s ADU permits Public-record counts in five jurisdictions. Not a ranking, not a statewide census, and not a completion count. A B license is not an ADU grade. Read the study 735 Research · Builders and supply Who is building California’s ADUs, and where they are CSLB classifications for 735 companies, set against who is actually named on the permits in five jurisdictions. A license is not an ADU grade. This is not a ranking. Read the study 76.5% Research · Builders and supply How long do ADU builders last? What the license register says You sign a six-figure contract and the workmanship warranty runs for years. This measures how often the license on the other side of that contract is still standing — and it names nobody. Read the study 45.6 Research · Builders and supply The enforcement record against ADU contractors — and what it does not record What the public license register actually says about discipline, at what rate, for what reasons — and the much larger question of what a consumer cannot see on it at all. Read the study

Types of ADU

Garage conversions, junior ADUs, prefab, and the legal distinctions that change which rules apply to yours.

21/21 Database · ADU types Pre-approved ADU plans Which California cities actually have a catalog you can use — and which only have a process page with nothing on it. Read the study 49.1% Research · ADU types Garage conversions: the most common ADU permit in Los Angeles Half the ADU permits the city issues are not new buildings. They are an existing structure being reclassified as somewhere a person may sleep — which is a fire, Read the study 3 Research · ADU types HUD Code, factory-built, or site-built? Three legal regimes hide behind one marketing word. Which one your unit is in decides who inspects it, what foundation it sits on, and whether it is real property. Read the study 9.6% Research · ADU types Junior ADUs: the category almost nobody uses Cheaper, smaller, faster to occupancy — and one unit in every ten. The legal distinction that defines the category is also the best explanation of why it stays small. Read the study 75% / 1 in 4 Research · ADU types ADUs and aging in place: the multigenerational case The demand evidence is AARP’s and the occupancy evidence is CCI’s, cited as theirs. The accessibility half is taken from the code, where the answer is more surprising than the brochures suggest. Read the study

The rules we hold ourselves to

Primary sources only
Statistics are traced to the organization that produced them. We do not repeat a figure because other sites repeat it, and we do not cite a secondary source when the primary file is downloadable.
Calculation is labeled as calculation
Where we compute a share, a ratio, a median or a range from source data, it says so. Nothing we derive is presented as a reported statistic, and nothing third-party is presented as our research.
Geography is in the first screen
A figure from five cities is a five-city figure. A figure from California HCD is a California figure. Nothing from our store is titled as a national ADU statistic.
Limitations sit above the fold on a flagship
Each study carries a limitations section. Where a result depends on a reporting quirk, a missing application date, or a city that does not publish contractor names, we say so in the finding rather than below it.
A license is not an ADU grade
California has no ADU contractor classification. Permit evidence is engagement in a named jurisdiction. It is not quality, completion, or a statewide track record.
Terner is cited, never restated
The Terner Center owns much of the homeowner-facing ADU research in California. Complementary supply-side and permit-versus-completion work is ours. Their findings stay in their voice.
Attributed to the desk, never to a person
Research here is published under the HyreADU Research Desk. We do not put an individual byline on original analysis, and we do not claim first-hand experience the organization cannot evidence.
Not legal, tax or financial advice
Zoning is local. Underwriting is a lender decision. Appraisal practice varies by appraiser and market. A disclaimer is not a substitute for naming the actual rule.

Every figure in one place

The studies above each answer one question in depth. ADU statistics collects the figures they produce into a digest, each labeled as a HyreADU calculation, a federal or state published figure, or a trade estimate — and each linked back to the study that produced it.

A statistics page ships only when at least a third of its figures are ours. Below that it would be a bibliography, and we would rather publish the study.

Using this research

Journalists, researchers, planning departments and housing reporters are welcome to cite and reproduce these findings, including the tables. We ask for a link to the study page, because the methodology and the limitations live there and a figure quoted without them is easy to misread.

Every study names its source files precisely enough to be checked independently. The query that produced a permit extract is published next to the extract.

If you find an error, we would rather hear it than not. Corrections are made on the page with a dated note, not silently. Write to hello@hyreadu.com.

The desk itself

How the research is made, what the statute actually says this month, and the files themselves. These are the pages the other fifty cite.

How Standards · The desk Methodology The three provenance classes, the sourcing-with-retrieval-date rule, the one-third gate on the statistics hub, the correction policy, and the California-only limitation stated plainly. Open 36 Timeline · The desk ADU ordinance change log Every section of Government Code Chapter 13 with its enactment line read verbatim from the code. 18 of 36 sections still carry only the 2024 SB 477 line. Open 8 Index · The desk ADU legalization index A HyreADU-constructed measure of published transparency — explicitly not of program quality, and not a ranking. Unretrievable cells are excluded, never scored zero. Open 3,828 Downloads · The desk Data downloads Nine CSVs, 3,828 rows, cut from the same files the studies read. Each carries a caveat line: declared valuation is not cost, a permit is not a completion, FMR is not asking rent. Open CC BY Press · The desk For the press There is no coverage to list yet, and none is invented here. What there is: how to describe the desk, twelve citable facts with sources, the open data, and CC BY 4.0 terms. Open

Questions

Where do the numbers on these studies come from?

Primary sources only: municipal building-permit open data in Los Angeles, San Francisco, Sacramento, San José and unincorporated Marin, HCD’s Housing Element Annual Progress Report, HUD Fair Market Rents, Census ACS housing tables, the California Contractors State License Board, and the ADU statute itself. Each study names the source files it read and the date they were retrieved.

Is this research national or California only?

California. Figures drawn from the HyreADU company store are titled to California, and figures drawn from permit extracts are titled to the five named jurisdictions they came from. Where a study reaches beyond California it rests on a federal or statutory source such as HUD Fair Market Rents, Census ACS or the GSE selling guides, and says so.

How often is the research updated?

Each study carries its own published date, a retrieval date for every source, and a data-as-of line. Annual pages such as the California ADU annual report keep one permanent URL and are republished when HCD releases the next Annual Progress Report. Corrections are made on the page with a dated note rather than silently.

Can I reuse these figures or tables?

Yes. Journalists, researchers and planning departments are welcome to cite and reproduce the findings, including the tables. We ask for a link back to the study page, because the method and the limitations live there and a figure quoted without them is easy to misread.

Do you rank ADU builders?

No. California licenses no ADU classification and no ADU grade, so there is nothing to rank on. Where contractor names appear they carry a public-record permit count in a named city and a retrieval date, with no score attached.

Who writes the research, and is it advice?

Every study is attributed to the HyreADU Research Desk rather than to an individual. Nothing on these pages is legal, tax or financial advice, and HyreADU does not design, permit or build accessory dwelling units.

Written and audited by

HyreADU Research Desk

Primary-source research, data analysis and fact checking

We are a research desk, not a builder. We read the permit extract, the statute, the HCD return or the fee schedule ourselves, and publish each figure with its source and retrieval date.

Where a number cannot be traced to a primary source, we leave it out and say what we could not verify. Our store-based claims cover California only.

CA: the only state this desk will make store-based claims about
5: jurisdictions with extracted ADU permit evidence
735: CSLB-verified companies in the California store
0: national claims from a one-state store

How this desk works

Primary sources only. Permit counts come from the city or county that issued the permit. Production counts come from HCD’s Annual Progress Report. Rents come from HUD or the Census. We do not cite an article that cites a source; we download the source and compute the figure ourselves.
This is a California site. The company store is 734 California firms and one New Mexico firm. Permit evidence exists for five named jurisdictions: Los Angeles, San Francisco, Sacramento, San José and unincorporated Marin. A number from that store is titled to those places, never to the United States.
A permit is not a completion, and a license is not an ADU grade. California licenses no ADU classification. Being named on an ADU permit is evidence of engagement in that jurisdiction, not of quality, completion, or work anywhere else. Owner-builder permits are excluded from contractor counts.
Calculation is labeled as calculation. Figures we derive are never presented as something HCD, HUD, the Census or a city published. Terner Center research is cited as Terner’s, never restated as ours.
We do not design, permit or build ADUs, and we take no payment for placement, ranking or a favorable mention. Pages that look like rankings are not: they publish public-record counts and let the reader decide.
Nothing here is legal, tax or financial advice. Zoning, underwriting and appraisal practice vary by jurisdiction, lender and appraiser. The useful next step on a specific lot is the planning counter and a licensed professional.

Data as of Municipal permit extracts through 2026-08-29; sources re-retrieved September 2026. Authorship on this site is organizational: the analysis belongs to the desk rather than to a named individual, and we do not publish credentials we do not hold. Our editorial policy sets out how we source, date and correct what we publish.

Sources & retrieval dates

California Department of Housing and Community Development — Annual Progress Report , Jurisdiction-level ADU and JADU permits issued and units completed Retrieved 2026-09-05.
LADBS building permits issued (data.lacity.org resource xnhu-aczu) , The legacy extract that still carries contractor of record; contractor evidence ends 2023-05-19 Retrieved 2026-08-29.
California Contractors State License Board — Check a License , License classification, status and published disciplinary actions Retrieved 2026-08-30.

A study describes a market. A lot is a lot.

None of this tells you whether your property can take an ADU, what it will cost, or who should build it. Those are questions about a specific parcel in a specific city.

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HyreADU does not design, permit or build accessory dwelling units. Research is informational. It is not legal, tax, financial or construction advice.