SF2369: ADU Regulation

Requires counties and cities to permit at least one ADU on the same lot as a single-family residence in zoning districts where such residences are principal uses. It refines how the size of ADUs is calculated, excludes unfinished basements, and removes the ability to restrict ADUs based on state historic building codes. Instead, it allows regulation of ADUs in historic districts only if deemed incongruous by the relevant preservation authority, who must document its reasoning. The bill also clarifies how 'size' is defined for these purposes.

Key Points & Impacts

• Counties and cities must allow at least one ADU per lot in zoning districts permitting single-family residences as a principal use.

• ADU size calculations must exclude unfinished basements, potentially allowing for larger ADUs than previously permitted if basements are unfinished.

• Removes the restriction allowing state historic building codes to prohibit or limit ADUs; only deed restrictions or rules of common interest communities can do so.

• ADUs may be regulated in historic preservation districts or areas of historical significance only if the relevant commission or city determines the proposed ADU would be incongruous with the area's character and documents its reasoning.

• Defines 'size' for ADU purposes as the gross living area of the primary dwelling, excluding garages, decks, and unheated porches, providing clarity for compliance.

• The bill prohibits more restrictive ADU regulations on common interest communities compared to single-family residences in general zoning.

• If a manufactured or mobile home is used as an ADU, it must be placed on a permanent foundation and assessed for real estate taxes as real property.

• Establishes a higher threshold for limiting ADUs in historic districts, shifting decision-making from blanket code restrictions to specific, documented determinations.

Signed by Governor on April 9. Takes effect July 1, 2026.