Navigating San Antonio's ADU Regulations: What Property Owners Need to Know
Accessory dwelling units have become one of the most talked-about housing topics in San Antonio over the past few years. Whether you call them casitas, granny flats, garage apartments, or ADUs, the concept is the same: a smaller, self-contained living space on the same lot as your primary home. And with rising property taxes and housing costs across the city, more homeowners are looking at ADUs as a way to generate rental income, house family members, or just make better use of their property.
San Antonio has taken real steps to make ADUs more accessible. The City updated its Unified Development Code in late 2022 with nearly 200 amendments, several of which specifically addressed ADU regulations. The City also released a set of permit-ready ADU floor plans that homeowners can use to streamline the permitting process. But the rules still have nuances that trip people up if they're not paying attention.
This post walks through the current ADU regulations in San Antonio so you know what's allowed, what's required, and what to watch out for.
What Qualifies as an ADU in San Antonio?
An ADU is a secondary residential unit on the same lot as a single-family home. To qualify as an ADU under the City's code, it needs to have a bedroom, a bathroom, and a kitchen or kitchenette, along with a separate entrance. It can be a detached structure in the backyard, an attached addition to the primary house, a garage conversion, or even an internal conversion of existing space within the home.
The UDC distinguishes between detached ADUs (which it refers to as ADDUs) and attached ADUs (referred to as accessory apartments). The rules are slightly different for each, so it matters which type you're building.
Zoning and Where You Can Build
ADUs are permitted by right in most single-family and rural residential zoning districts in San Antonio, meaning you don't need a special use permit or rezoning to build one. However, the specific zoning classification of your property determines the setback requirements, lot coverage limits, and other development standards that apply.
Before you start planning, verify your property's zoning on the City's One Stop GIS map. If your property is zoned for single-family residential use, you're likely eligible. If you're in a historic district or subject to a neighborhood conservation district, additional design review may apply.
One important requirement that's easy to overlook: your property must be platted. If your lot was never formally platted or if the plat doesn't meet current standards, you may need to address that before a building permit will be issued.
Size and Height Restrictions
San Antonio's UDC limits the size of an ADU relative to the primary dwelling. The ADU cannot exceed 25% of the gross floor area of the main house, though the specific maximum varies depending on whether the unit is attached or detached.
For detached ADUs, the height limit is 25 feet or two stories, whichever is less. Detached ADUs are also limited to one bedroom. Attached ADUs must comply with the height regulations of the underlying zoning district, which in most single-family zones means the same height limit as the primary structure.
Lot coverage matters too. The total footprint of all structures on the lot, including the primary house and the ADU, cannot exceed the lot coverage percentage allowed by your zoning district. This is where smaller lots can run into problems, especially in older neighborhoods where the existing house already takes up a significant portion of the lot.
Setbacks
Detached ADUs must be at least three feet from the side and rear property lines. They must also be fire-rated on walls within three feet of a property line and cannot have eave overhangs that encroach into the setback. Attached ADUs follow the same setback requirements as the primary dwelling under the applicable zoning district.
Getting setbacks right is critical. A setback violation can stop your permit application or create legal issues with neighbors after the fact. If you're not sure about your property lines, get a survey before you start designing.
Owner Occupancy
This is the rule that catches the most attention. San Antonio requires the property owner to reside on the premises, either in the primary dwelling or in the ADU, for the ADU to be legally occupied. An affidavit confirming owner occupancy must be filed and recorded in the public records.
This means you can't buy a property, build an ADU, and rent out both units while living somewhere else. The owner has to live on site. This requirement also affects short-term rentals. Non-owner-occupied short-term rentals in ADUs are prohibited under the current city ordinance.
Parking
An additional off-street parking space is required only for ADUs larger than 800 square feet. For smaller units, no additional parking beyond what's already required for the primary dwelling is needed. This is a significant change from older regulations that required parking for all ADUs and made it impractical to build them on many lots.
Utilities and Infrastructure
ADUs must connect to the primary dwelling's existing utility infrastructure, including water, sewer, and electrical systems. The existing infrastructure needs to be able to support the additional unit without requiring upsizing or extension. If your water or sewer service can't handle the added load, that's something you'll need to address with SAWS before permitting.
Depending on the size and scope of your ADU project, you may also need to coordinate with CPS Energy for electrical service upgrades, particularly if the ADU includes a separate panel or heavy electrical loads like HVAC equipment.
The Permit Process
The City of San Antonio has worked to streamline ADU permitting. The Development Services Department offers permit-ready ADU floor plans that have already been reviewed and approved for code compliance. These plans cover the building design but are not site-specific, meaning you'll still need a site plan that shows how the ADU fits on your particular lot, including setbacks, utility connections, and drainage.
If you're using a custom design rather than a permit-ready plan, the review process takes longer because the building plans need full code review. Either way, you'll need a building permit from DSD before construction can start.
For homeowners earning 80% or less of the area median income, the City may waive ADU permitting fees. Check with DSD for current eligibility requirements.
What Property Owners Should Think About Before Building
ADUs aren't complicated, but they do require some upfront homework. Before committing to a project, there are a few things worth checking beyond the zoning and code requirements.
Deed restrictions can prohibit ADUs even if the City's zoning allows them. Many older neighborhoods in San Antonio have deed restrictions that limit the number of structures on a lot or restrict rental use. These restrictions are enforced privately, not by the City, so a building permit won't protect you if your deed restrictions say otherwise.
Flood zone status matters. If your property is in a FEMA Special Flood Hazard Area, the ADU will need to be elevated above the base flood elevation and may trigger additional permitting requirements. Check your flood zone before you start designing.
Drainage and impervious cover can become an issue. Adding a structure increases the impervious cover on your lot, which affects stormwater runoff. On lots that are already close to the maximum impervious cover allowed by the zoning district, this can be a constraint.
And if you're planning to use the ADU as a rental, understand the owner occupancy requirement and the short-term rental restrictions before you invest. Building an ADU with a business plan that doesn't comply with the current rules puts you at risk.
Getting Help
Most homeowners can navigate the ADU process on their own using the City's permit-ready plans and working directly with DSD. But if your lot has complications like tight setbacks, flood zone issues, drainage constraints, or utility limitations, it may be worth bringing in a civil engineer to evaluate the site and help you work through the permitting process.
If you're thinking about building an ADU on your property in San Antonio and want to understand how your specific lot factors into the equation, we're happy to take a look.
