Highland, CA Accessory Structures: ADU Rules (2026)

Highland Municipal Code § 16.44.180 implements the state ADU and junior ADU laws in the City of Highland. An application is considered ministerially, without discretionary review or a hearing, under either "planning review" or a streamlined "building permit only" review. The city must act within 60 days from the date it receives a completed application when a single-family or multifamily dwelling already exists on the lot. If the ADU is submitted with a permit for a new single-family dwelling, the city can delay acting until it acts on the dwelling, and an applicant-requested delay tolls the 60-day period. The application must be signed by the parcel owner or owners.

Under planning review, the director of community development or designee approves an ADU that meets every standard. One ADU is allowed on a lot with a proposed or existing primary dwelling in a residential zone. No ADU can be built in an area designated as a high fire severity zone, or in an area without adequate sewer systems, meaning a septic tank system.

Size is capped. An attached ADU cannot exceed 50 percent of the primary dwelling's gross floor area, except where that would prevent an ADU of 850 square feet, or 1,000 square feet for an ADU with more than one bedroom. An attached or detached ADU with two or more bedrooms cannot exceed 1,200 square feet, and no ADU can be smaller than an efficiency unit under California Health and Safety Code Section 17958.1. Height cannot exceed the district limit, the primary dwelling's height, or the applicable Government Code Section 66321(b)(4) height, whichever is greatest.

Setbacks: none for an ADU within an existing structure or one rebuilt in the same location with the same dimensions; four feet from side and rear lot lines for all others. Front yard setbacks still apply, except where they would prevent an 800-square-foot ADU. The ADU must match the primary dwelling's colors and materials, an attached ADU needs a separate exterior entrance, and fire sprinklers are required if the primary dwelling has them. The building permit route follows Government Code Section 66323, and a JADU must be between 150 and 500 square feet.