Open-license CSV of every California city's annual ADU permit count, merged from two authoritative sources. Free for any use with attribution. Updated quarterly as HCD publishes new APR data.
5,152 rows. Schema: Place, Year,
ADU_Permits, Type, Partial.
Coverage: 471 California cities + 38 county jurisdictions.
Years: 2013–2025 (2025 partial — 360 of ~509 jurisdictions
filed by HCD's April 1, 2026 deadline).
Suggested citation:
BackyardADU.net (2026). California ADU Permits Dataset 2013–2025
(May 2026 release). Sources: Big West Coast ADU Dataset (Peterson,
2024) for 2013–2017; California HCD Annual Progress Report
(April 2026 snapshot) for 2018–2025. Retrieved from
backyardadu.net/data/.
| Column | Type | Description |
|---|---|---|
Place | string | City or county jurisdiction name. Title-cased. County-unincorporated rows end in "County". |
Year | int | Calendar year permit was issued. |
ADU_Permits | int | Number of ADU building permits issued in that year by that jurisdiction. |
Type | string | "city" for incorporated cities, "county" for county-unincorporated jurisdictions. |
Partial | string | "Y" if the year's data is still trickling in (currently 2025 only); empty otherwise. Exclude partial rows when computing milestones like all-time peaks. |
2013–2017 (legacy): Big West Coast ADU Dataset published by BuildinganADU.com (Kol Peterson, January 2024 release). Drawn from city building-department records aggregated and normalised by Karen Chapple's research team at the UC Berkeley Center for Community Innovation. The dataset's January 2024 release covers 2013–2022; we use it for 2013–2017 only because HCD's APR framework didn't begin systematic ADU-line-item tracking until 2018.
2018–2025 (current): California HCD Housing
Element Annual Progress Report (APR) Table A2, downloaded from
data.ca.gov on 2026-05-01 (HCD
last refreshed the file 2026-04-24). Filter:
UNIT_CAT='ADU' AND BP_ISSUE_DT1 non-empty
(building permit was actually issued, not just entitled). We sum
NO_BUILDING_PERMITS per row, treating empty/0 as 1
(~96% of rows are 1, the rest are project-level rollups of 2–12
permits). City names are normalised from HCD's UPPERCASE format to
Title Case to match the legacy data.
Why the source mix: our previous published dataset used Big West Coast for all years through 2022. HCD's data has been continuously refreshed since the January 2024 BWC snapshot as cities re-file with corrected counts; the 2022 figure was 24,851 in BWC vs 31,750 in HCD's current snapshot — a 28% upward revision largely from late and corrected filings. We migrated 2018+ to HCD-current values in this release so the methodology is one consistent source for all post-preemption years (2018–present).
The merged CSV is offered free for any use with attribution. Underlying sources retain their own licenses:
Our merged file (the cross-walking, normalisation, and partial-year flagging) is dedicated to the public domain (CC0). Cite as above.
HCD publishes the APR data in three rounds each year:
Subscribe via the city pages or the about page to get notified when the dataset is refreshed.
Email hello@backyardadu.net. We're particularly interested in: (1) error reports if a city's reported number contradicts your local knowledge, (2) journalists or researchers who want a specific custom analysis (we usually do these for free, attribution requested), and (3) academics who want to collaborate on a deeper methodology paper.