Houston, TX Accessory Structures: ADU Rules (2026)

Houston's historic preservation ordinance, Chapter 33 Article VII, requires a certificate of appropriateness before altering, adding to, or constructing anything on a landmark, protected landmark, or contributing structure in one of the city's designated historic districts; § 33-236(b) makes it unlawful to build any exterior feature within a historic district without one. Ordinarily that certificate has to go before the Houston Archaeological and Historical Commission (HAHC), a citizen board, under the eleven compatibility criteria in § 33-241. 1(c) lets the city's planning director bypass the HAHC and approve certain projects administratively, and item (5)a on that list covers accessory dwelling units directly: construction of freestanding garages, including garage apartments, freestanding carports, and other secondary structures, that have a footprint of 600 square feet or less, located at the rear of the lot.

Anything larger, or built anywhere other than the rear of the lot, has to go through the full HAHC review under § 33-241, which weighs massing, materials, and distance from the property line against neighboring contributing structures. Because Houston has no zoning code, this historic-district size cap is the only citywide numeric limit on garage apartments and similar secondary units found anywhere in the Code; outside a historic district, a homeowner adding a garage apartment answers only to Chapter 10 building-safety rules and the Chapter 42 platting standards on building lines and lot coverage, not to a use-based ADU ordinance. 1(g).