Can you build an ADU in Calabasas or Hidden Hills?

Is Calabasas part of the City of Los Angeles for ADU purposes?

No. Calabasas is a separate city with its own municipal code, its own planning counter and its own ADU ordinance, which the state reviewed in 2026 ³. Hidden Hills, the gated city next door, incorporated on October 19, 1961 and runs its own building and planning department ²⁹. ZIMAS, LADBS and the LA City ADU memos we cite elsewhere do not apply to either one.

What the two cities share with the Valley is the fire department. Both contract with the Consolidated Fire Protection District of Los Angeles County, the county fire department, which lists Calabasas and Hidden Hills among the cities it serves ¹⁵, and the county's fire prevention plan-check list assigns both to its Calabasas office ¹⁶.

Zip code 91302 straddles the city line. If your property tax bill says Los Angeles, our Woodland Hills fire zone guide and Canoga Park and West Hills guide are the ones to read.

What are the ADU rules in Calabasas right now?

As of October 2026, state ADU law is the rule that counts in Calabasas, because the city's own ordinance has been found non-compliant. The city's ADU ordinance is No. 2020-382, adopted January 22, 2020 ³. On May 4, 2026, the California Department of Housing and Community Development (HCD) issued formal findings that it fails to comply with state ADU law and gave the city until June 3, 2026 to respond ³. HCD's handbook spells out what that means: while an ordinance is non-compliant, the city must apply state standards until it adopts a compliant one ⁹.

The findings letter names the local rules that cannot be enforced against you, among them:

• A zoning clearance before your permit. HCD says a separate zoning clearance is unauthorized and would thwart the 60-day approval deadline ⁴.
• A 30 percent rear-yard coverage cap. HCD calls the city's Table 2-4 standard unlawful wherever it would not permit an 800 sq ft ADU ⁶.
• A one-story, 16-foot cap on detached units. HCD told the city to add the state's other height allowances ⁵.
• A rule that the ADU's design must conform to the main house, which HCD calls overreaching, ambiguous and subjective ⁷.

The state baseline is one detached backyard house of up to 800 sq ft with 4-foot side and rear setbacks, at 16, 18 or 20 feet depending on the conditions in Government Code section 66321 ¹⁰; our setbacks and JADU versus ADU guides cover the rest. Ask the Calabasas Community Development Department in writing whether a replacement ordinance has been adopted since HCD's letter.

Is my Calabasas or Hidden Hills lot in a fire zone, and does that stop an ADU?

In Calabasas, yes, every house lot is in the fire zone, and no, that does not stop an ADU by itself. We tested the center point of every single-family parcel in both cities against the 2025 Local Responsibility Area Fire Hazard Severity Zones in the county's GIS ²:

• Calabasas: 3,049 of 3,049 single-family parcels are in the Very High zone.
• Hidden Hills: 364 of 540 (67 percent) are Very High, 87 (16 percent) High, 55 (10 percent) Moderate and 34 (6 percent) outside any wildland zone.

These are the maps the state fire marshal issued for Los Angeles County on March 24, 2025, and a local agency may not lower the level the state recommended ¹⁷. Hidden Hills' own notice confirms the city contains Moderate, High and Very High zones ¹⁹.

The zone changes how you build, not whether. Properties in High or Very High zones may be subject to California Building Code Chapter 7A, the ignition-resistant construction chapter, and to defensible-space rules under Public Resources Code 4291 ¹⁸. Sprinklers are separate: the state says they cannot be required in an ADU if they are not required for the existing main house, and the ADU cannot trigger a sprinkler requirement for the main house ¹³. Our fire zone guide and fire sprinkler guide cover the construction details.

Hidden Hills' housing element promises an extra ADU beyond state law, but only on lots outside the High and Very High zones and off private streets with reduced fire access, to be written into the zoning code by June 2026 ²³. For two-thirds of Hidden Hills lots, that bonus unit is off the table.

Can the Hidden Hills Community Association stop my ADU?

It cannot prohibit one, but it will review it, and the two reviews are tangled in a way nobody else in the Valley deals with. Nearly all of Hidden Hills has been inside the gated Hidden Hills Community Association since the city incorporated, under CC&Rs recorded from 1950 on, and the city says it has no authority to modify or remove them ²⁰. The Association says the city building inspector will not issue a permit unless the plans carry architectural approval stamped and signed by two committee members ²⁶, and the city's ADU page says a completed application includes HHCA Architectural Committee approval ²⁴.

The Association's rules were written for guest houses, not ADUs. The 1950 declaration allows a guest house without a kitchen, for non-paying guests of the main house ²⁷. The current architectural standards allow one single-story guest house without a kitchen, prohibit renting it, allow kitchens only in four named tracts, and cap guest houses at 1,200 sq ft ²⁸.

State law sits above all of that. HCD says Civil Code sections 714.3 and 4751 nullify CC&Rs and operating rules that effectively prohibit or unreasonably restrict an ADU on a single-family lot ¹¹. An HOA may impose limited objective standards such as materials or architectural style, but nothing stricter than state ADU law that raises the cost or blocks the unit, and no fees ¹². HCD also told Calabasas in December 2025 that an HOA, as a third party, cannot influence approval of an ADU application ⁸, which sits uneasily beside Hidden Hills' requirement that a complete application include HHCA approval. Whether a no-kitchen or no-rental rule survives section 4751 on your tract is a question for an attorney; our Porter Ranch guide lists what HCD treats as an unreasonable restriction.

How big are the lots, and is there room for a backyard house?

There is room on almost every lot. We measured every single-family parcel in the two cities on the LA County Assessor's parcel map ¹:

• Calabasas: 3,049 parcels, median lot 10,817 sq ft, half of all lots between 8,643 and 15,027 sq ft.
• Hidden Hills: 540 parcels, median lot 53,357 sq ft, about 1.2 acres, half between 47,583 and 68,426 sq ft.

Hidden Hills zoning explains the gap: its RA-S zones require one acre, the R-1 zone allows 20,000 sq ft but holds only five parcels, and the city says most lots are at least an acre ²¹. An 800 sq ft backyard house covers under 2 percent of a one-acre lot and under 8 percent of the Calabasas median. Neither city may set a minimum lot size for an ADU ¹⁴; slope, fire access and the Association's setbacks decide where it goes, not the area.

Hidden Hills residents are already doing this. The city reports 15 ADUs built during the last housing cycle and expects at least four a year going forward ²². Its preapproved-plan program accepts detached new units of 250 to 800 sq ft and one story up to 16 feet, with a 30-day decision once an application is complete, though no plans had been preapproved as of its last update ²⁵²⁴.

What should I check first for a Calabasas or Hidden Hills address?

Start with which city you are in, then the fire map, then the paperwork.

1. The city. Your property tax bill names it, and each city has its own planning counter ³²⁹.
2. The fire zone. In Calabasas assume Very High; in Hidden Hills check the 2025 state map for your parcel ²¹⁹. Plan on Chapter 7A construction and defensible space either way ¹⁸.
3. The current ordinance. In Calabasas, ask in writing whether a compliant ordinance has replaced No. 2020-382; until then state standards apply ³⁹. In Hidden Hills, ask whether the June 2026 zoning amendments were adopted ²³.
4. The Association, in Hidden Hills. Get the consolidated architectural standards and your tract's declaration, and file with the Architectural Committee early ²⁶²⁸.
5. Sprinklers. Find out whether the main house is required to have them, because that decides whether the ADU must ¹³.

Quick answers

Sources

1. LA County Assessor parcel layer (LACounty_Parcel), single-family parcels with TaxRateCity Calabasas and Hidden Hills, LA County Assessor (Greenlight analysis). Facts checked 2026-10-13
2. LA County GIS Hazards layer 18, Fire Hazard Severity Zones LRA (2025), matched to single-family parcels in Calabasas and Hidden Hills, LA County Fire Department GIS / CAL FIRE via LA County eGIS (Greenlight analysis). Facts checked 2026-10-13
3. Review of the City of Calabasas' ADU Ordinance under State ADU Law (findings letter, May 4, 2026), California Department of Housing and Community Development (HCD). Facts checked 2026-10-13
4. HCD findings letter to Calabasas (May 4, 2026), item 6, Zoning Clearance, California Department of Housing and Community Development (HCD). Facts checked 2026-10-13
5. HCD findings letter to Calabasas (May 4, 2026), item 11, Height limit, California Department of Housing and Community Development (HCD). Facts checked 2026-10-13
6. HCD findings letter to Calabasas (May 4, 2026), item 9, Site Coverage for Detached Rear Yard Units, California Department of Housing and Community Development (HCD). Facts checked 2026-10-13
7. HCD findings letter to Calabasas (May 4, 2026), item 8, Subjective Standards, California Department of Housing and Community Development (HCD). Facts checked 2026-10-13
8. HCD Letter of Technical Assistance to Calabasas (Dec. 5, 2025), Updates to the ADU Handbook (2025), on HOAs, California Department of Housing and Community Development (HCD). Facts checked 2026-10-13
9. Accessory Dwelling Unit Handbook (March 2026), Local ADU Ordinances and Local Agencies, California Department of Housing and Community Development (HCD). Facts checked 2026-10-13
10. Accessory Dwelling Unit Handbook (March 2026), 66323 Units: Single-Family Detached ADUs, California Department of Housing and Community Development (HCD). Facts checked 2026-10-13
11. Accessory Dwelling Unit Handbook (March 2026), Homeowners Associations (HOAs), on Civil Code §§ 714.3 and 4751, California Department of Housing and Community Development (HCD). Facts checked 2026-10-13
12. Accessory Dwelling Unit Handbook (March 2026), Homeowners Associations (HOAs): what restrictions can be placed on an ADU, California Department of Housing and Community Development (HCD). Facts checked 2026-10-13
13. Accessory Dwelling Unit Handbook (March 2026), Fire Protection and Fire Sprinkler Requirements, California Department of Housing and Community Development (HCD). Facts checked 2026-10-13
14. Accessory Dwelling Unit Handbook (March 2026), Lot size, California Department of Housing and Community Development (HCD). Facts checked 2026-10-13
15. Board Letter 25-0839 (Feb. 18, 2025), letterhead list of cities served by the Consolidated Fire Protection District, County of Los Angeles Fire Department. Facts checked 2026-10-13
16. LACoFD Plan Check and Inspection Offices (Fire Prevention Offices: Engineering Plan Check, 03/26/2026), County of Los Angeles Fire Department. Facts checked 2026-10-13
17. CAL FIRE Releases 2025 Local Responsibility Area Fire Hazard Severity Zone Maps for Los Angeles County, City of La Cañada Flintridge. Facts checked 2026-10-13
18. CAL FIRE Releases 2025 LRA Fire Hazard Severity Zone Maps for Los Angeles County: why the maps matter, City of La Cañada Flintridge. Facts checked 2026-10-13
19. Just Released: New Fire Hazard Severity Maps (Apr. 25, 2025), City of Hidden Hills. Facts checked 2026-10-13
20. City of Hidden Hills 2021-2029 Housing Element (May 2025), Appendix A history and IV.B Non-Governmental Constraints, City of Hidden Hills. Facts checked 2026-10-13
21. City of Hidden Hills 2021-2029 Housing Element (May 2025), IV. Constraints, Zoning Designations, City of Hidden Hills. Facts checked 2026-10-13
22. City of Hidden Hills 2021-2029 Housing Element (May 2025), review of the prior Housing Element, Program 5b, City of Hidden Hills. Facts checked 2026-10-13
23. City of Hidden Hills 2021-2029 Housing Element (May 2025), Program 6c, ADU Allowance Beyond State Law, City of Hidden Hills. Facts checked 2026-10-13
24. Accessory Dwelling Unit (ADU's): Preapproved ADU Plan Submittal Process, Streamlined 30-day Approval, City of Hidden Hills. Facts checked 2026-10-13
25. Accessory Dwelling Unit (ADU's): Preapproved ADU Plan Submittal Process, Step 1 eligibility and plan status, City of Hidden Hills. Facts checked 2026-10-13
26. Architectural Committee Overview, Hidden Hills Community Association. Facts checked 2026-10-13
27. Hidden Hills Declaration No. One of Protective Restrictions (Dec. 8, 1950), Article II Section 8, Accessory Buildings or Structures, Hidden Hills Community Association (recorded CC&Rs). Facts checked 2026-10-13
28. Architectural Standards of the Hidden Hills Community Association (adopted May 20, 2008, amended through August 2019), Guest Houses, Hidden Hills Community Association. Facts checked 2026-10-13
29. History of Hidden Hills, City of Hidden Hills. Facts checked 2026-10-13

Greenlight is not a contractor, architect or engineer, and this is not legal advice. Rules change; every fact here shows the date we last checked it.