Count the backyards.
City by city.

From the state. California Government Code section 65400 requires every city and county to report its housing element progress to HCD each year, by April 1 for the year before. Table A2 of that Annual Progress Report lists the housing developments a jurisdiction entitled, permitted or completed during the year, with a unit category, the number of units issued building permits and the permit date. HOMEFRONT adds up those units for each jurisdiction and year, once for the ADU category and once for every category. Nothing is estimated. One rule is applied: a unit counts only in the year its permit was issued.

Why these totals are lower than a straight sum of the state table. Some reports also list units whose permits were issued in an earlier year, next to a later milestone such as completion. Summing every permit row in the 2025 reports for the five counties gives 26,778 ADUs; 7,430 of those carry a permit date outside 2025, nearly all of them earlier. Leaving them out counts each permit once, in the year it was issued.

1. 01Source: HCD, Housing Element Annual Progress Report data, Table A2, data.ca.gov edition of October 13, 2026, retrieved October 14, 2026.
2. 02Scope: the 186 cities and county governments in the five counties that appear in the table, reporting years 2018–2025.
3. 03Count: units issued building permits whose permit date falls in the reporting year, grouped by jurisdiction. Rows dated outside the reporting year are left out.
4. 04Checks: the jurisdiction rows add up exactly to a separately queried state total for every county and year, and permit totals match their income breakdown. No address or parcel detail is kept.

Citing this index: HOMEFRONT Compass, “SoCal ADU Permit Index, 2018–2025,” homefrontremodelingca.com/compass/adu-permit-index/, compiled from California HCD Annual Progress Report data (Table A2), updated October 14, 2026.