ADU rules in San Antonio

Detached ADUs (the UDC calls them accessory detached dwelling units, ADDUs) are allowed accessory to a house, limited to one accessory unit per lot located in the rear yard. Development Services lists the eligible base districts as R-1 through R-6, RM-4, RM-5, RM-6, and multifamily properties up to five total units; Table 311-1a also lists Dwelling - Accessory as permitted in the UD, RD, and FR districts. The FR Farm and Ranch district has its own scheme allowing up to two ADDUs per property. Approval is by permit, not public hearing.

Attached ADUs are allowed: the UDC definition of accessory dwelling covers both an accessory detached dwelling unit and an accessory apartment, a secondary unit located within the same building as the principal dwelling. Attached units follow the setbacks and height limits of the primary structure's zoning district rather than the relaxed detached-unit setbacks, and the same size formula applies to both.

Every eligible property can build an ADU of at least 800 sq ft regardless of house size; larger homes can go up to half the primary home's floor area with an absolute 1,600 sq ft ceiling. Attached units follow the district height limit. Citywide accessory-structure rules also cap all accessory structures at 50 percent of the side plus rear yard area and 2,500 sq ft of total floor area in residential districts.

The property owner must occupy either the principal unit or the ADU as their permanent residence and may never collect rent on the owner-occupied unit. Compliance is enforced through a notarized affidavit plus a covenant recorded in Bexar County public records that binds future owners; a property with no owner on site must instead be rezoned to a district allowing more than one dwelling unit. The 2023 UDC amendments (Ord. 2022-11-03-0831, effective January 1, 2023) kept this requirement. The one exception is the FR Farm and Ranch district, where the owner is not required to live on the property.

The 2023 amendments put the operative rule in the ADU section itself, and the city's fact sheet and ADU permits page state flatly that only ADUs over 800 sq ft require a dedicated space. The older citywide schedule (Table 526-3a in §35-526) still carries a 1-per-unit minimum row for Dwelling - Accessory, so DSD's interpretation favors the specific ADU provision; both texts are noted here because the conflict exists in the code.

In the districts where ADUs are allowed they are permitted by right; there is no conditional use or public hearing step, but an accessory dwelling permit must be issued before the unit is built or occupied. The process is a standard residential building permit through the BuildSA portal, with the recorded owner-occupancy affidavit included in the application packet, followed by plan review, inspections, and a certificate of occupancy.

§35-371(a)(4) makes §35-374.01 binding on ADUs used as STRs, and City Code Chapter 16 Article XXII requires the permit itself; DSD cross-references ADU permits against STR applications. Note that the residential use matrix (Table 311-1) does not list short-term rentals as permitted in the small-lot R-3, R-2, and R-1 districts even though ADUs themselves are allowed there.