Why San Antonio Homeowners Are Building Backyard ADUs & Casitas
An Accessory Dwelling Unit (ADU)—often called a backyard casita, granny flat, or in-law suite—is a self-contained residential structure built on the same lot as your primary single-family home.
Across San Antonio, Alamo Heights, Boerne, and Kerrville, families are building ADUs to house aging parents close by with full independence, create a quiet detached executive office, or generate long-term rental income.
2026 ADU Construction Cost Ranges in San Antonio
Because an ADU is a complete miniature house—requiring its own foundation, roof, bathroom plumbing, kitchen, HVAC, and electrical panel—per-square-foot costs are higher than simple bedroom additions.
- Garage Conversion ADU (400–550 sq. ft.): $65,000 – $105,000 (Utilizes existing slab and roof framing while adding insulation, plumbing trenching, mini-split HVAC, bathroom, kitchenette, and new windows/entry).
- Detached Studio or 1-Bedroom Casita (450–650 sq. ft.): $115,000 – $175,000 (Includes new engineered concrete slab, 2x6 framing, exterior siding/stone matching the main home, full bath, kitchen, and utility tie-ins).
- Custom 1–2 Bedroom Luxury Guest House (700–1,000+ sq. ft.): $180,000 – $265,000+ (Includes vaulted ceilings, covered porch, full-size kitchen appliances, laundry closet, and premium architectural finishes).
San Antonio Zoning, Setbacks & Utility Trenching Considerations
Before designing your ADU, we verify four critical site factors: (1) Municipal zoning and HOA covenant rules, (2) Rear and side property line setbacks (typically 5 feet minimum for accessory structures in CoSA, though utility easements may require more), (3) Impervious cover limits, and (4) Sewer gravity fall from the backyard to your main house cleanout.
If the backyard sits lower than your main sewer line, we install a sealed residential sewage ejector pump system to pump wastewater reliably uphill to the municipal tie-in.