Las Cruces, NM Accessory Structures: ADU Rules (2026)

Section 38-33A of the Las Cruces Land Development Code defines an accessory dwelling unit (ADU) as a self-contained living quarter with its own kitchen, attached to and under the same roof as the main dwelling. An ADU may be created by converting an existing single-family house, adding onto one, or building the extra living space into new construction. The zoning districts where ADUs are allowed are EE, RE, REM, R-1c, R-1a, R-1b and their manufactured-home equivalents (R-1cM, R-1aM, R-1bM).

Nine conditions govern every ADU. The owner of record must reside in either the main house or the ADU for at least six months of each calendar year, with an exemption only for hospitalization or a similar medical emergency. Only one ADU is allowed per lot, and it must be built solely to house family members, not the general public. A conversion or addition can enlarge the home by no more than 30 percent of its heated and cooled floor area, and new construction can devote no more than 30 percent of its floor area to the ADU. The lot must meet the underlying zoning district's minimum area, and no more than ten percent of eligible single-family lots within a 500-foot radius may already have an ADU, capping density neighborhood by neighborhood. Exterior changes must match the main house's design, materials and color, and the ADU must connect to the main dwelling through a shared wall at least four feet long with a doorway at least three feet wide, opening onto genuine living space rather than a garage or hallway. Homes on septic systems cannot install a second septic tank for the ADU. If the property changes hands and the new occupant of the ADU is not a family member, or if any condition is violated, the ADU use becomes void immediately and the structure must be reconverted to a single-family dwelling or a new approval obtained.