Westminster, CA Accessory Structures: ADU Rules (2026)

Setback rules split converted units from new construction. Converting existing living space or an existing accessory structure into an ADU requires no new setback at all, and a rebuilt unit in the same footprint as the structure it replaces is likewise exempt. Every other new ADU must keep a minimum four-foot setback from side and rear lot lines and still meet the applicable front-yard setback for the zone. On a single-family lot, a newly built detached ADU must sit at least six feet from the primary dwelling and from any other detached accessory structure; on multifamily-zoned land it must be at least ten feet from other dwelling units and six feet from accessory structures.

Underlying zone standards such as lot coverage still apply, but the city cannot use them to block an ADU of at least 800 square feet. An ADU built above an existing structure, or containing a second floor, must also meet the primary dwelling's setback and lot-coverage rules. Applications are ministerial: the Division must approve or deny a complete application within 60 days, and a denial must come with a written list of defects and how to fix them; missing that deadline means automatic approval. No impact fee applies to any ADU under 750 square feet, and fees for larger units scale with the primary dwelling's square footage.

An ADU cannot be sold separately from the primary home, and neither an ADU nor a JADU may be rented for stays under 30 days.