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Altadena ADU regulations

Altadena follows County of Los Angeles’s ADU rules. Here are the requirements that apply to an ADU in Altadena. In Altadena, a detached ADU can be up to 1,200 sq ft, with a maximum height of 16 ft.

Los Angeles area Local figures verified: October 2026 State law updated: October 2026

At a glance

1,200 sq ftDetached ADU size16 ftDetached ADU height4 ftSide & rear setbacks1 ADU + 1 JADUADUs on a single-family lot

Altadena, CA

What you can build in Altadena.

Altadena is one of many California jurisdictions encouraging ADUs: small homes built on the same lot as a single-family home or multi-family building that add living space, rental income and much-needed housing.

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Zoning

All properties zoned for single-family and multi-family use may be eligible to build ADUs.

Number of ADUs

Depends on how your lot is zoned.

  • Lots zoned for single-family use may add 1 ADU and 1 Junior ADU (JADU).
  • Lots with an existing multi-family building may add up to 8 detached ADUs (no more than the number of existing units) plus conversion ADUs in non-livable space, at least one and up to 25% of the existing units. Lots with a proposed multi-family building may add up to 2 detached ADUs. (State law since January 2025; some local codes have not caught up, and state law controls.)

Building size

Maximum floor area by ADU type.

JADUMax 500 sq ft
Detached ADUMax 1,200 sq ft
Attached ADU50% of the primary residence floor area
Multi-family property ADUNo maximum

Building height

Maximum height by ADU type.

Detached ADU16 ft (18–20 ft near transit or on a lot with a multistory dwelling)
Attached ADUUp to 25 ft or the zone’s height limit, whichever is lower (state law)
Multi-family property ADU16, 18 or 20 ft depending on transit proximity and lot

Setbacks

Minimum distance from property lines.

Side yard4 ft
Rear yard4 ft

Parking

California state law.

No parking is required for an ADU if any of the following is true:

  • The ADU is within one-half mile walking distance of public transit.
  • The ADU is within an architecturally and historically significant historic district.
  • The ADU is part of the proposed or existing primary residence or an accessory structure.
  • On-street parking permits are required but not offered to the ADU’s occupant.
  • A car-share vehicle is located within one block of the ADU.
  • No replacement parking is required when a garage, carport or uncovered parking space is removed or converted to build an ADU (expanded by SB 1211, 2025).
Before you plan around these numbersLocal ADU rules change often, and your lot’s shape, utilities and easements matter as much as the city code. Our free ADU analysis confirms exactly what you can build on your property in Altadena.

Sources: Governed by Los Angeles County (Title 22 §22.140.640); California Government Code §§66310–66342.

We build herePlanning an ADU in Altadena? See how we design and build here: Altadena ADU builder.

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