A garage apartment is a dwelling on the second floor of a detached garage. In San Antonio, it falls under the detached ADU rules: two stories and 25 feet maximum, the same floor-area cap, and the owner-occupancy affidavit. Whether the garage area counts toward the ADU's size is a question we confirm with the city during design.
Can my existing garage take a second floor?
Usually not without work. Garage slabs are often poured without the footings a second story needs. An engineer evaluates the foundation; if it falls short, a new two-story building is typically cleaner than retrofitting.
What should the design solve?
- Stairs. An outside stair saves garage space but needs a landing and a code-compliant guard.
- Heat. A second floor under a South Texas roof needs strong attic insulation and careful HVAC sizing.
- Neighbors. Upper windows facing side yards affect privacy, so placement matters.
- Fire separation. The garage below must be separated from the living space above.
How do setbacks work for a two-story unit?
The same side and rear minimums apply: 3 feet with fire-rating and eave limits, or 5 feet to avoid them. On a narrow lot, the stair often sets the footprint more than the building.
What does it cost?
We did not find a reliable published San Antonio range specific to garage apartments as of October 2026. Expect it to price above a one-story cottage of the same living area, because you are also building the garage. Your written, itemized quote breaks out both parts. See the cost guide for general ranges.