Iron County, UT Accessory Structures: ADU Rules (2026)

Section 17.36.400(B)(1) requires an ADU to share the same water, sewer, power and gas connections as the primary dwelling; if it ties into an existing septic system, the owner must get written verification from the Southwest Utah Public Health Department that the system is sized for the added load. The ADU must provide at least one extra off-street parking space beyond what the primary dwelling requires, and any garage or carport parking lost to the conversion must be replaced elsewhere on the lot. An addition-type ADU is capped at eight hundred square feet; a footprint ADU is capped at fifty percent of the primary dwelling's size.

It must meet all applicable building, health and fire codes and be designed so the home still reads as a single-family dwelling from the street. Section 17.36.400(B)(2) bars an ADU inside a mobile home as defined in Section 17.80.010, on any lot of six thousand square feet or less, or built as a duplex under the current adopted building code. Section 17.36.400(C) distinguishes an ADU from a guest house: an ADU is permitted by right in any residential zone that allows a single-family dwelling, while a guest house needs an administrative land use permit, must sit at least fifteen feet from the primary dwelling, and has no size cap. The zoning administrator reviews compliance under Chapter 17.72.