In short
- 31 ADU permits since 2018.
- 6 in 2025.
About this data
- Source: California HCD Housing Element Annual Progress Reports. The state data does not say whether an ADU is detached, attached, a garage conversion or a JADU, so most records show as 'unknown'. Permit valuations are not published in this source. Timelines use the application date the city reported to the state, matched to the permit where possible; some cities report their planning application date, so timelines can include planning review. Each project is counted once, in its building-permit year (or completion year when no permit date was reported).
- Hidden Hills reported no ADUs for 2024.
Permits by year
Permits by year and type (table)
| Year | All ADU permits | Garage conversions | Detached |
|---|---|---|---|
| 2018 | 1 | — | — |
| 2019 | 3 | — | — |
| 2020 | 4 | — | — |
| 2021 | 7 | — | — |
| 2022 | 8 | — | — |
| 2023 | 2 | — | — |
| 2024 (incomplete report) | 0 | — | — |
| 2025 | 6 | — | — |
“—” means the source for that year does not report ADU type.
Read more: ADU types explained
ADU rules in Hidden Hills
State law check: No HCD review letter on file; the ordinance was rewritten in January 2026. HCD has told other cities that HOA review of an ADU violates state law (see the note below).
| Rule | Hidden Hills' code | State law guarantees |
|---|---|---|
| Maximum size | State-law ADU: 800 sq ft detached. Locally regulated ADU: 850 sq ft (studio or 1 bedroom) or 1,000 sq ft (2+ bedrooms), attached 50% of the house; up to 1,200 sq ft if all zone standards are met. Junior ADU 500 sq ft. | At least 850 sq ft (1,000 sq ft with 2+ bedrooms) must be allowed; an 800 sq ft detached ADU always is. Conversions of existing space have no size cap. Junior ADU: up to 500 sq ft. |
| Height | State limits; a locally regulated ADU is one story (attached ADUs may have two). | Detached: at least 16 ft (18 ft within ½ mile of transit, plus 2 ft for a matching roof). Attached: 25 ft or the zone's limit, whichever is lower. |
| Setbacks | 4 ft side and rear; 50 ft front setback for a locally regulated ADU; 25% lot coverage. | No more than 4 ft side and rear; none for conversions of existing space. |
| Parking | 1 space per ADU or per bedroom, whichever is less, unless exempt; no replacement parking. | At most 1 space; none within ½ mile of transit and in several other cases. No replacement parking when a garage is converted. |
| Owner living on site | None for ADUs. Junior ADU: required unless it has its own bathroom. | None for ADUs. A junior ADU that shares a bathroom with the house requires the owner to live in one of them. |
| How many on a single-family lot | The full state set. | One ADU converted from existing space, one junior ADU and one new detached ADU (up to 800 sq ft). From January 1, 2027: two new detached ADUs (a city then needn't allow a junior ADU on that lot). |
| Short-term rentals | Not for less than 30 days. | No guarantee: cities may require rentals of more than 30 days, and junior ADUs can't be short-term rentals. |
- The city's ADU page says an application includes the homeowners association's architectural approval; state guidance says an HOA review can't hold up an ADU permit.
- The whole city is in a Very High Fire Hazard Severity Zone.
Where local rules conflict with state law, state law controls. Sources: Hidden Hills Municipal Code Title 5, Ch. 2, Art. P (Ord. 407, Jan 12, 2026); HCD's list of review letters; California ADU rules. Verified Sep 29, 2026. Rules change and every lot is different: confirm with the city before you design.
How long permits take
| Type | Median days, application to permit | Middle half | Permits |
|---|---|---|---|
| Unclassified | too few to say | 5 |
Middle half: the range covering the middle 50% of permits (a quarter were lower, a quarter higher).
Read more: How long ADU permits take in Los Angeles (and other cities) · How long ADUs take to build
What neighbors declared as cost
Cost data (declared permit valuations) is not published for this area in these sources.
Read more: How to choose an ADU builder
An ADU builder serving Hidden Hills? Feature your business on this page.
Questions about ADUs in Hidden Hills
How many ADUs have been permitted in Hidden Hills?
Public records show 31 ADU permits in Hidden Hills from 2018 through 2025. 6 in 2025. These counts come from the city's reports to the state, which place a project in its completion year when no permit date was reported.
Can I build an ADU on my property in Hidden Hills?
California law allows ADUs on most lots with a house, including in Hidden Hills, but what you can build depends on your lot, local rules and utilities. This site shows permits, not eligibility. See California ADU rules.
Where do I apply for an ADU permit in Hidden Hills?
Apply with the City of Hidden Hills' Building and Safety and Planning department, which has a pre-approved ADU plan program. Official ADU page.
How current is this?
- State annual progress reports: through 2025 (published once a year)
How our data works · Download the data · Free to reuse with credit to SoCal ADU Tracker (socaladutracker.com), under CC BY 4.0.