San Antonio, TX Accessory Structures: ADU Rules (2026)

Sec. 35-371 of the Unified Development Code governs accessory dwellings, also called carriage houses, granny flats, or ECHO (elder cottage housing opportunity) units, in San Antonio's single-family residential zoning districts. Living area in an accessory dwelling cannot exceed 800 square feet, or 50 percent of the primary structure's gross floor area (excluding covered porches) up to a ceiling of 1,600 square feet, in any single-family district other than "FR"; the ceiling drops to 1,200 square feet in the "RE" district. No accessory dwelling may be constructed, used, or occupied until the city issues an accessory dwelling permit under subsection (a)(2).

For accessory detached dwelling units (ADDUs), only one is allowed per lot and it must sit in the rear yard. An ADDU exceeding 800 square feet of gross floor area must provide one on-site parking space. The required setback from the rear and side property lines is 5 feet, reduced to 3 feet if the structure has no roof overhang. Height is capped at 25 feet or two stories. Attached accessory dwelling units instead follow the setbacks of the primary structure required by the underlying zoning district rather than the detached-unit standards.

Any ADDU operated as a short-term rental must separately comply with Sec. 01's short-term rental standards. These provisions were most recently amended by Ordinance No. 2022-11-03-0831, effective January 1, 2023.