Statistics
ADU cost statistics
62 of 108 figures are HyreADU calculations. The 2018–19 owner survey as its authors published it, the construction-cost indices that have moved since, and the declared permit valuations five California cities actually recorded — each labeled, none collapsed into a sticker price.
Written by HyreADU Research Desk Primary-source research and data analysis
Audited by HyreADU Research Desk Provenance-class and indexation audit
How to use this page
There is no sourced sticker price for a California ADU, and this page does not ship one. The only statewide owner survey with a published method — Chapple, Ganetsos and Lopez, UC Berkeley Center for Community Innovation, 22 April 2021, of homeowners who permitted or completed a unit in 2018 or 2019 — found a median construction cost of $150,000, or $250 per square foot, inclusive of design, labor, materials and permits, with regional medians from $100,000 in Los Angeles County to $177,500 in the Bay Area.
Those are 2018–19 dollars from owners who finished. Construction got more expensive afterwards. The DGS California Construction Cost Index rose from 6,924 in December 2019 to 10,633 in August 2026, a factor of 1.536.
Applying that factor cell-by-cell puts the statewide median at about $230,351 ($384/sf) and a detached unit at about $276,421 ($461/sf).
That indexation is a HyreADU calculation on somebody else’s survey. It is not a 2026 survey and it is not a bid, and DGS itself says the index “does not reflect current market bidding environment.” A third number circulates as if it were cost and is not: declared permit valuation.
Median declared valuation runs $40,000 in the City of Los Angeles to $156,800 in unincorporated Marin, and on Los Angeles new detached permits the declared rate is $120/sf against $461/sf indexed — about 26%.
62 of 108 figures on this page are HyreADU calculations (62 hyreadu calculation, 10 agency published, 36 trade / survey estimate). Every calculation links to the study that produced it. Nothing here is a quote. HyreADU does not design, permit or build accessory dwelling units.
Read the provenance, not just the number
Almost every “ADU cost” page on the open web ends its citation chain in a builder brochure. That is why the spine of this digest is provenance rather than volume. Every figure below is exactly one of three things, and the class travels with it into every table.
Trade / survey estimate — Chapple, Ganetsos and Lopez (CCI, 22 April 2021, Terner-reviewed) and the Terner Center’s own August 2020 brief. A survey of owners who built in 2018 and 2019, and an average from a professional report.
Cited as theirs, in their dollars, with their vintage attached.
Agency published — DGS republishing the ENR Building Cost Index for California, Census and HUD publishing the constant-quality house price index, ENR publishing its 20-city averages, a city publishing a valuation rate on a numbered form.
We cite the table, never an article about the table.
HyreADU calculation — the indexation, the declared-valuation distributions, the per-square-foot rates, and every ratio between them. Method on the California cost study and the permit-valuation study.
Those three classes describe three different objects, and the whole failure mode of the category is treating them as one. A survey median is what a household said it spent. An index level is a labor-and-materials trend.
A declared valuation is a number written on a permit application to generate a fee. A contractor’s bid — the only number that can actually be spent — appears nowhere on this page, because we do not have one for your lot and will not invent one.
A fourth object circulates and is not on this page at all: the round per-square-foot band with no vintage, no geography, no sample and no method. “California ADUs run $300–$500 a foot” is a sentence, not a statistic. We record that it circulates. We do not repeat it as a fact.
The figures most worth knowing
Full method on the California cost study. A range with named movers is the evidence. A starting price is marketing.
The 2021 owner survey, as its authors published it
Chapple, Ganetsos and Lopez sent postcards to 15,745 addresses drawn from HCD Annual Progress Report records for 2018 and 2019 ADU permits and certificates of occupancy, plus a Bay Area supplement. They received 823 responses, a 4.8 per cent rate after dropping non-owners.
Construction cost was defined as “the total cost that the homeowner spent on their ADU, and is inclusive of all costs for design, labor, materials, and permits.” Every figure in this table is theirs, in 2018–19 dollars.
| Cut of the survey | Median total | Median $/sf | Class | What that cut is |
|---|---|---|---|---|
| Statewide | $150,000 | $250/sf | Trade / survey estimate | Inclusive of design, labor, materials and permits. |
| San Francisco Bay Area | $177,500 | $329/sf | Trade / survey estimate | Most expensive region in the survey; 52% of respondents lived here. |
| Central Coast | $140,000 | $223/sf | Trade / survey estimate | Region as defined by the authors. |
| Orange and San Diego Counties | $130,000 | $200/sf | Trade / survey estimate | Combined in the report because of sample size. |
| Los Angeles County | $100,000 | $197/sf | Trade / survey estimate | Cheapest region; garage conversions were 39% of the LA County sample. |
| Detached (new construction) | $180,000 | $300/sf | Trade / survey estimate | 53% of the sample. Most expensive type. |
| Addition to the main residence | $150,000 | $250/sf | Trade / survey estimate | 13% of the sample. |
| Garage conversion or expansion | $90,000 | $189/sf | Trade / survey estimate | 23% of the sample. Cheapest type. |
| Conversion of the main residence | $100,000 | $173/sf | Trade / survey estimate | 9% of the sample. Lowest $/sf among conversions. |
| Studio | $100,000 | $241.27 | Trade / survey estimate | 18% of units in the survey were studios. |
| 1-bedroom | $150,000 | $266.67 | Trade / survey estimate | 61% of units. |
| 2-bedroom | $212,500 | $250.00 | Trade / survey estimate | Most expensive by total. 17% of units. |
| 3 or more bedrooms | $200,000 | $129.17 | Trade / survey estimate | 3% of units. Lowest $/sf — wet rooms sink across more floor area. |
| Owner income under $50,000 | $95,000 | $176.17 | Trade / survey estimate | Owners who spent less, not a cheaper market. |
| Owner income $100,000 or more | $170,000 | $306.12 | Trade / survey estimate | 70% of respondents were in this band. |
Chapple, Ganetsos and Lopez, Implementing the Backyard Revolution: Perspectives of California’s ADU Owners, Center for Community Innovation, 22 April 2021, Table 2 and related text. Retrieved 2026-09-05. Average unit in the sample: 615 square feet. 37 per cent of units cost under $100,000; 71 per cent under $200,000.
The survey’s own limits are the figures’ limits, and they are not small. Respondents were more affluent than California homeowners generally (70 per cent at $100,000 or more, against 40 per cent of Californians in the 2019 ACS).
The Bay Area was over-represented at 52 per cent of respondents; Los Angeles County was under-represented at 24 per cent of respondents against 54 per cent of the postcard population. And every respondent finished. Nobody who priced a unit and stopped is in this table.
The survey against the indexation
The left pair of columns is Terner/CCI’s. The right pair is ours: the same medians multiplied by 1.536, the ratio of the California Construction Cost Index in August 2026 (10,633) to December 2019 (6,924).
An index moves every cell by the same factor. It does not know that garage conversions became a smaller share of Los Angeles production, or that a 750-square-foot fee threshold changed the size mix, or that one lot needs a new sewer and the next does not.
| Cut | Survey median (2018–19) | Survey $/sf | Indexed to Aug 2026 | Indexed $/sf | Class of the indexed pair |
|---|---|---|---|---|---|
| Statewide | $150,000 | $250/sf | $230,351 | $384/sf | HyreADU calculation |
| San Francisco Bay Area | $177,500 | $329/sf | $272,582 | $505/sf | HyreADU calculation |
| Central Coast | $140,000 | $223/sf | $214,994 | $343/sf | HyreADU calculation |
| Orange and San Diego Counties | $130,000 | $200/sf | $199,637 | $307/sf | HyreADU calculation |
| Los Angeles County | $100,000 | $197/sf | $153,567 | $303/sf | HyreADU calculation |
| Detached (new construction) | $180,000 | $300/sf | $276,421 | $461/sf | HyreADU calculation |
| Addition to the main residence | $150,000 | $250/sf | $230,351 | $384/sf | HyreADU calculation |
| Garage conversion or expansion | $90,000 | $189/sf | $138,211 | $291/sf | HyreADU calculation |
| Conversion of the main residence | $100,000 | $173/sf | $153,567 | $266/sf | HyreADU calculation |
Indexed columns are a HyreADU calculation: survey median × 1.536. DGS’s own qualifier travels with the number — the underlying ENR Building Cost Index “reports cost trends for specific construction trade labor and materials in the California market and does not reflect current market bidding environment.”
A second index is a useful check on whether the choice of index is driving the result.
The Census and HUD constant-quality Laspeyres price index of new single-family houses under construction moved from 134.4 (annual 2019) to 199.8 (July 2026 preliminary), a factor of 1.487.
On that factor the statewide median indexes to $222,991 rather than $230,351 — a difference of $7,360, or about 3% of the level. Two indices, two indexed dollars, one five-year-old survey underneath all of it.
The national house index is not California and is published here only as that check.
Declared permit valuation in five jurisdictions
Declared permit valuation is the number a homeowner is most likely to be shown as “what ADUs cost around here,” because it is the only ADU dollar figure California cities publish at scale. Declared valuation is a fee input.
The applicant writes it on the building-permit application, the city computes plan check and permit fees from it, and some cities substitute a published dollar-per-square-foot table instead. Everything in this table is a HyreADU calculation on municipal open data.
| Jurisdiction | Window (issued) | n (> $0) | p25 | Median | p75 | Garage median | Non-garage median | Class |
|---|---|---|---|---|---|---|---|---|
| City of Los Angeles | 2017-02-28 → 2023-05-19 | 3,809 | $20,000 | $40,000 | $81,000 | $27,000 | $80,000 | HyreADU calculation |
| City and County of San Francisco | 2015-06-26 → 2026-08-28 | 1,314 | $83,625 | $150,000 | $250,000 | $185,000 | $145,300 | HyreADU calculation |
| City of Sacramento | 2018-10-29 → 2026-07-24 | 749 | $85,000 | $133,105 | $195,313 | $80,000 | $150,000 | HyreADU calculation |
| City of San José | 2008-02-11 → 2026-08-27 | 459 | $71,819 | $98,971 | $131,648 | $73,800 | $107,023 | HyreADU calculation |
| Marin County (unincorporated) | 2014-04-10 → 2026-07-20 | 277 | $55,000 | $156,800 | $350,000 | $122,500 | $168,000 | HyreADU calculation |
HyreADU calculation from five municipal permit harvests generated 29–30 August 2026. Nested permit valuations; owner-builder-named contractor records excluded under Business and Professions Code § 7044; zero and missing valuations dropped. Declared permit valuation, not construction cost. Assembled 2026-09-05.
The extract windows are not the same and cannot be made the same: Los Angeles contractor evidence ends 19 May 2023 because the legacy LADBS extract is the only shape carrying a contractor of record, and the newer feeds dropped those columns.
Means are omitted from the headline columns because a single $17.5 million Los Angeles row and Marin’s long right tail pull them. Medians and quartiles are the statistic.
What the cities were told, per square foot
Dividing declared valuation by the floor area recorded on the same permit removes the size difference between a 480-square-foot conversion and a 1,200-square-foot detached unit, and leaves a rate that can be set beside a construction-cost rate.
On 8,528 City of Los Angeles new detached ADU permits — median recorded floor area 920 square feet — the declared median is $120/sf. The whole declared distribution sits below the cheapest indexed anchor.
| Measure | Value | What kind of number it is | Class | Source |
|---|---|---|---|---|
| Declared valuation per square foot — 10th percentile | $96/sf | A fee input recorded on a permit | HyreADU calculation | LADBS pi9x-tg5x, 8,528 new detached ADU permits |
| Declared valuation per square foot — 25th percentile | $102/sf | A fee input recorded on a permit | HyreADU calculation | LADBS pi9x-tg5x |
| Declared valuation per square foot — median | $120/sf | A fee input recorded on a permit | HyreADU calculation | LADBS pi9x-tg5x |
| Declared valuation per square foot — 75th percentile | $152/sf | A fee input recorded on a permit | HyreADU calculation | LADBS pi9x-tg5x |
| Declared valuation per square foot — 90th percentile | $201/sf | A fee input recorded on a permit | HyreADU calculation | LADBS pi9x-tg5x |
| Indexed cost per square foot — garage conversion | $291/sf | Somebody else’s survey, indexed by us | HyreADU calculation | Survey $189.19/sf × 1.536 |
| Indexed cost per square foot — statewide, all types | $384/sf | Somebody else’s survey, indexed by us | HyreADU calculation | Survey $250/sf × 1.536 |
| Indexed cost per square foot — detached | $461/sf | Somebody else’s survey, indexed by us | HyreADU calculation | Survey $300/sf × 1.536 |
| Ratio: median declared ÷ indexed detached | 26% | A comparison of two different instruments | HyreADU calculation | $120/sf ÷ $461/sf |
| Ratio: median declared ÷ indexed garage conversion | 41% | A comparison of two different instruments | HyreADU calculation | $120/sf ÷ $291/sf |
| Median recorded floor area on those permits | 920 sq ft | A city record | HyreADU calculation | LADBS pi9x-tg5x, n = 8,536 |
HyreADU calculation on City of Los Angeles open data and on the indexed 2021 survey. Full method, and the reasons the two instruments were never measuring the same scope, on the permit-valuation study.
Part of that four-to-one gap is scope, not under-declaration, and the honest form of the finding says so. A permit valuation is at best the value of the permitted construction work.
An owner-reported cost includes design, engineering, plan-check and impact fees, site work outside the permitted structure, financing costs and the contractor’s margin.
The defensible claim is about the ratio between two independent instruments measured on the same units, in the direction the mechanism predicts.
It is not a decomposition, and it accuses no applicant of anything.
The fee lines a sample of schedules actually publishes
Fees are not construction cost and they do not scale with it. There is no statewide ADU fee average on this site, because there is no 480-jurisdiction table behind one.
What follows is a sample of published municipal schedules, with the arithmetic labeled wherever we added published cells together ourselves. The fee digest at ADU fee statistics takes this further.
| Published figure | Amount | Jurisdiction | Schedule date | Class | Whose arithmetic |
|---|---|---|---|---|---|
| Building Division total, ADU 0–750 sq ft (issuance + plan review + inspection) | $3,291 | City of San José | 10 Aug 2026 | HyreADU calculation | Cells are the city’s ($422 + $1,137 + $1,732). The addition is ours. |
| Building Division total, ADU 751–1,200 sq ft | $5,103 | City of San José | 10 Aug 2026 | HyreADU calculation | Cells are the city’s ($633 + $1,950 + $2,520). The addition is ours. |
| Plan review plus permit issuance on a $150,000 declared valuation | $4,337 | City and County of San Francisco | Table 1A-A, 12 Jul 2026 | HyreADU calculation | DBI’s published band: plan review $1,617 + $15.60 per additional $1,000; issuance $677 + $4.83 per additional $1,000. The arithmetic is ours. |
| ADU fee estimate at 749 sq ft, excluding school fees | $5,272 | City of Sacramento | CDD-0419, 12 Jul 2026 | Agency published | The city’s own column total on its own worksheet. |
| ADU fee estimate at 750 sq ft, excluding school fees | $10,624 | City of Sacramento | CDD-0419, 12 Jul 2026 | Agency published | The city’s own column total. |
| The step between those two columns, for one square foot | $5,353 | City of Sacramento | CDD-0419, 12 Jul 2026 | HyreADU calculation | Subtraction of two city-published totals. Park $2,617.50 + SAFCA $1,575 + STA $1,154.64 arrive at 750 sq ft. |
| Valuation rate used for new living area | $170.80/sf | City of Sacramento | CDD-0245, 12 Jul 2026 | Agency published | The city’s published table. Where a table governs, declared valuation stops being an estimate. |
| Valuation rate used for a garage conversion | $101.16/sf | City of Sacramento | CDD-0245, 12 Jul 2026 | Agency published | Same table. |
A sample of five published municipal schedules retrieved 2026-09-05, not a census of California’s roughly 480 cities and counties. Where a total is HyreADU arithmetic on published cells, the cells are named so the addition can be checked.
Impact fees are barred outright on an ADU of 750 square feet of interior livable space or less by Government Code § 66311.5(c)(1) — the section formerly numbered § 66324, and before that § 65852.2(f).
Connection and capacity charges are excluded from that definition, and school developer fees run on a different statute with a 500-square-foot test. Sacramento’s worksheet is the rare municipal document that prints the cliff as three columns.
Figures we will not repeat
- An “ADUs start at $X” starting price
The 2021 survey found 37 per cent of units under $100,000 and 71 per cent under $200,000 — among 2018–19 owners who finished, with garage conversions pulling the left tail hard in Los Angeles County.
A starting price is a marketing floor, not a minimum the statute, the indices or the permit files support. We do not publish one, and the California cost study does not either.
- A statewide average per square foot with no vintage
Inside the survey alone, the median rate runs from $197/sf in Los Angeles County to $329/sf in the Bay Area, and by type from $173/sf to $300/sf.
Indexed to August 2026 those spans widen in dollars. A single number across that range hides the two variables — region and type — that did the most work in the only survey we have.
- The indexed dollar quoted as a 2026 measurement
$230,351 is a 2018–19 owner median multiplied by a labor-and-materials index. It is on this page because it is the honest way to say “that survey is old” without inventing a new survey.
It is not a 2026 owner survey, it is not a contractor’s price, and DGS says the underlying index does not reflect the bidding environment. We label it every time it appears, and so should anyone who cites it.
- Declared permit valuation restated as construction cost
If declared valuation were cost, contractor-named ADUs in the City of Los Angeles would be a $40,000 product and San Francisco a $150,000 product, and both would contradict the owner survey, the Terner average, and anyone who has paid a carpenter in either city.
San José’s harvest maximum of exactly $234,848 is the clearest tell that a table is doing the work: a market of bids does not produce a ceiling that neat.
- A construction-cost figure derived from a fee schedule, or the reverse
Fees are computed from valuation or from floor area, and they step at statutory thresholds. Construction cost is what a household pays a builder.
A page that adds a permit total to a per-square-foot rate and calls the result a budget has double-counted the parts a valuation table already flattened, and missed the site work and utilities neither number contains.
What actually moves a project along the range
Type does more work than any other single variable in the survey. Detached new construction had a median of $180,000 against $90,000 for garage work — a factor of two on the same statewide sample, and the indexed figures preserve it exactly, because an index cannot change a ratio.
A conversion inherits a slab, walls and a roof. It still pays for insulation, egress, a wet room, electrical service and the parking the garage stops providing.
A detached unit pays for all of that plus a foundation, an envelope and a utility run.
Region is labor, not atmosphere. The Terner Center attributed the Los Angeles / Bay Area gap “largely” to labor costs, and the 2021 survey found an ADU gap larger than Terner’s own multifamily hard-cost work: Bay Area ADUs sat $106 per square foot above the next most expensive region.
Indexed, the Bay Area median is 1.78× the Los Angeles County median.
The CCCI itself is built only from Los Angeles and San Francisco ENR data, which means it cannot speak for Sacramento, Fresno or Bakersfield — a limitation of the index, stated by the people who publish it.
Site and utilities do not scale with floor area at all. A short sewer tie-in and a septic upgrade are not the same project. A flat pad and a hillside retaining wall are not the same project.
A panel with spare capacity and a service upgrade with a transformer wait are not the same project. Fourteen per cent of 2021 respondents put utility connections among their top challenges.
This is why a single dollar-per-square-foot figure is not merely imprecise but structurally wrong about the shape of the budget: part of the budget has no square footage in it.
Size crosses a fee threshold before it crosses a cost threshold. A unit at 749 square feet of interior livable space and a unit at 751 are separated by roughly two square feet of construction and, on Sacramento’s published worksheet, by $5,353 of fees.
That is not a cost driver in the construction sense. It is a statutory step, and it changes the total.
Who builds it changes which number applies. The Los Angeles legacy extract is majority owner-builder — 8,312 of 12,627 matched rows, excluded from the contractor harvest under Business and Professions Code § 7044 — and San Francisco excluded 671 owner-builder permits of 2,005.
An owner-builder’s declared valuation is not a general contractor’s bid, and the contractor-named distributions above are already the wrong frame for a homeowner who intends to be the builder of record.
HyreADU analysis. Put those five together and the reason there is no sticker price stops being a rhetorical position and becomes an arithmetic one.
Two 800-square-foot detached units on two California lots can differ by a sewer run, a slope, a school-fee threshold, a crane that will not fit down the side return, and a finish package — and every one of those differences is larger than the precision a statewide average implies.
The range is the finding. The cost calculator asks you to type the lines you actually have, and leaves the building rate at zero until a designer or a bid supplies one, because a $0 line you can see is more honest than a fabricated $300 per square foot.
Citing these figures
Journalists, planning desks and academics are welcome to cite these tables. Where possible, link the California cost study or the permit-valuation study rather than this digest: the method, the exclusions and the limits live there, and a digest that travels without them is exactly the artefact this page exists to argue against.
Where a figure is labeled HyreADU calculation, attribute it to HyreADU and name what it was computed from — “HyreADU indexation of the 2021 CCI owner survey on the DGS California Construction Cost Index,” or “HyreADU analysis of City of Los Angeles building-permit valuations.” Where it is Agency published, cite DGS, the Census Bureau, ENR or the named city; we are repeating it.
Where it is Trade / survey estimate, cite Chapple, Ganetsos and Lopez, or the Terner Center brief, with the 2018–19 or 2020 vintage attached — that vintage is part of the fact.
Corrections are welcome and are published on the page with a dated note rather than made silently: hello@hyreadu.com. If a post-2021 statewide ADU owner cost survey with a published method exists, it supersedes the survey half of this page and we want to know about it.
Questions
How much does an ADU cost to build in California?
What is a realistic ADU cost per square foot?
Why is the permit valuation so much lower than these figures?
Is a garage conversion really half the price of a detached unit?
Has construction inflation made the 2021 figures useless?
Did the Terner Center say ADUs cost $150,000?
How much are ADU permit fees in California?
Which figures on this page are HyreADU’s own?
Is any of this a quote?
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 Terner/CCI papers, DGS CCCI, Census/HUD construction price index and ENR 20-city tables retrieved 2026-09-05; five-city permit harvests generated 29–30 August 2026; LADBS resource pi9x-tg5x refreshed 2026-08-30. 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
- Karen Chapple, Dori Ganetsos and Emmanuel Lopez, Implementing the Backyard Revolution: Perspectives of California’s ADU Owners (UC Berkeley Center for Community Innovation, 22 April 2021) , Statewide owner survey drawn from HCD Annual Progress Report addresses for 2018–19 permits and certificates of occupancy. Median construction cost $150,000 / $250 per square foot, inclusive of design, labor, materials and permits. Table 2 regional and type cuts. 37% under $100,000; 71% under $200,000. Average unit 615 square feet. Terner Center staff reviewed it; cited here as CCI’s. Retrieved 2026-09-05.
- Karen Chapple, David Garcia, Eric Valchuis and Julian Tucker, Reaching California’s ADU Potential (Terner Center and Center for Community Innovation, August 2020) , Average ADU cost $167,000; Los Angeles $148,000; Bay Area $237,000; Bay Area costs that “can exceed $800 per square foot.” Footnote 6 cites Valchuis, “HomeOn,” MCP professional report, UC Berkeley, 2020, whose underlying table we did not retrieve and do not reconstruct. Retrieved 2026-09-05.
- California Department of General Services — California Construction Cost Index (CCCI) , ENR Building Cost Index averaged for San Francisco and Los Angeles only, republished monthly. December 2019 = 6,924; August 2026 = 10,633; factor 1.535673. DGS’s own qualifier: “The ENR BCI reports cost trends for specific construction trade labor and materials in the California market and does not reflect current market bidding environment.” Retrieved 2026-09-05.
- U.S. Census Bureau and HUD — Price Indexes of New Single-Family Houses Under Construction (Laspeyres, 2005 = 100) , Survey of Construction. Annual 2019 = 134.4; July 2026 preliminary = 199.8; factor 1.487. National, not Californian, and not ADU-specific. Published here as a check on whether the choice of index drives the indexation. Retrieved 2026-09-05.
- Engineering News-Record, Construction Economics, 17 August 2026 (20-city averages) , Construction Cost Index 14,350.29 (+0.3% month, +3.1% year); Building Cost Index 9,005.51 (+0.5% month, +4.7% year). The 20-city average is not California; CCCI is the Los Angeles and San Francisco derivative used for the arithmetic on this page. Retrieved 2026-09-05.
- Los Angeles Department of Building and Safety — Building Permits Issued from 2020 to Present , Socrata resource pi9x-tg5x on data.lacity.org. 409,619 rows downloaded; ADU frame 39,279 non-supplemental permits; refreshed 2026-08-30. Source of the per-square-foot declared-valuation distribution and the recorded floor areas. Retrieved 2026-09-05.
- HyreADU municipal permit harvests — Los Angeles, San Francisco, Sacramento, San José and unincorporated Marin , Generated 29–30 August 2026 from municipal open data. Nested permit valuations; owner-builder-named records excluded; zeros dropped; quartiles by linear interpolation on the sorted list. Helper file src/data/research/adu-cost-california-valuations.json, computed 2026-09-05. Declared permit valuation, not construction cost. Retrieved 2026-08-29.
- City of Sacramento — CDD-0419 Accessory Dwelling Unit Fee Estimate and CDD-0245 residential fee table (both revised 12 July 2026) , Worked fee columns at 749, 750 and 1,200 square feet, totalling about $5,271.90, $10,624.40 and $14,842.50 excluding school fees. Residential valuation table: new living area $170.80 per square foot; garage conversion $101.16 per square foot. Retrieved 2026-09-05.
- City of San José — Building and Structure Permits Fee Schedule, effective 10 August 2026 , ADU new construction and alteration: 0–750 sq ft issuance $422, plan review $1,137, inspection $1,732; 751–1,200 sq ft $633 / $1,950 / $2,520. ICC construction-tax valuation rates on page 25. Retrieved 2026-09-05.
- San Francisco Department of Building Inspection — Table 1A-A, building permit fees on and after 12 July 2026 , Plan review and permit issuance computed from total valuation. $50,001–$200,000 band: plan review $1,617 for the first $50,000 plus $15.60 per additional $1,000; issuance $677 plus $4.83 per additional $1,000. Note 1 excludes Public Works, Planning, Fire, Public Health and trade permits. Retrieved 2026-09-05.
- California Government Code § 66311.5 , The current ADU and JADU fee section, added by renumbering § 66324 by SB 543 (Stats. 2025, Ch. 520, § 7), effective 1 January 2026, after SB 477 recodified ADU law out of § 65852.2 in March 2024. Impact fees barred at 750 square feet of interior livable space or less; proportional above it; connection and capacity charges excluded from the definition. Retrieved 2026-09-05.
A range is not a quote. Type the lines you actually have.
Design, permits, site work, utilities, a building rate from a real bid, and the contingency you hold. The calculator will not fill in a national ADU price, and a $0 line you can see is more honest than a fabricated one.
HyreADU does not design, permit or build accessory dwelling units, and does not appraise, lend or prepare taxes. This page is informational. It is not a quote, a bid, or construction, legal, tax or financial advice.
Construction-cost survey figures from the Center for Community Innovation and the Terner Center are cited as theirs and are 2018–21 vintage.
Indexation of those figures by the California Construction Cost Index is a HyreADU calculation, not a 2026 owner survey, and the Department of General Services states that the index does not reflect the current market bidding environment.
Declared permit valuation is a fee input recorded by a city and is not construction cost; nothing on this page alleges under-declaration by any applicant.
Fee figures are a sample of published municipal schedules retrieved on 5 September 2026, not a census of California’s roughly 480 jurisdictions. Current ADU fee rules were retrieved at Government Code § 66311.5; citations to § 65852.2 or § 66324 are repealed numberings.