Can I add an accessory dwelling unit?

Often yes. The Land Use Matrix allows accessory dwelling units as a limited use in FD, SF-R, SF-6, SF-4.5, ND-3, ND-3.2, ND-3.5, CD-2.5, and CD-3, and as a permitted use in ND-4, N-CM, CD-2, CD-4, CD-5, and CD-5D. Where limited, Sec. 5.1.3.1(C) requires that the owner maintain their primary residence on the lot, that only one ADU exist on the lot, and that the habitable area not exceed the lesser of 1,000 square feet or half the principal dwelling's habitable area. The ADU building type standards in Sec. 4.4.5.1 and the district's accessory structure setbacks apply, one parking space is required (Table 7.1), and the ADU counts as a separate unit for occupancy restrictions. ADUs are not allowed in CD-1 or the special districts, and legacy districts follow the Chapter 9 matrix instead. San Marcos zoning applies inside the incorporated city limits only; Texas counties do not zone, and ETJ parcels have no municipal zoning. A further Development Code update was adopted on second reading June 16, 2026 but is not yet published, so confirm current standards with the Planning Division at 512-393-8230 before design, purchase, leasing, or permitting decisions.