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Building an ADU (casita) in San Antonio

City code and Texas law · Last reviewed October 9, 2026

San Antonio lets you add one accessory dwelling unit (ADU), which the city also calls a casita, on a lot in the R-1 to R-6 and RM-4 to RM-6 zoning districts, and in multifamily districts up to five total units. It can be up to 800 square feet or half the size of the main house, whichever is larger, but no more than 1,600 sq ft. You must live in the main house or the ADU and record an owner-occupancy affidavit and covenant with Bexar County. The city offers permit-ready casita plans and a forgivable-loan pilot program. Texas has no statewide ADU law, so these city rules decide. [1][2][3][4][5]

San Antonio at a glance
Zones that allow ADUsR-1 to R-6, RM-4, RM-5, RM-6, and multifamily districts up to five total units [1]
Number per lotOne ADU [1][2]
Max size800 sq ft or 50% of the main house, whichever is larger; never over 1,600 sq ft [1][2]
Detached ADU height25 ft or 2 stories [1][2]
Detached ADU setbacks5 ft from side and rear lines; 3 ft with no eave overhang (fire rating needed within 5 ft) [1][2]
LocationDetached ADU in the rear yard [2]
Parking1 space only for a detached ADU over 800 sq ft [1][2]
Owner occupancyRequired; notarized affidavit and recorded covenant [1][2]
UtilitiesShared or separate meters; separate meters need a separate address [1][6]
Initial plan reviewUp to 3 business days for first redline comments [1]
City helpForgivable loans up to $25,000 or $35,000 for eligible owners; permit-ready plans from $450 [3][4]
On this page
  1. At a glance
  2. What you can build in San Antonio
  3. Size, height and setbacks
  4. Owner occupancy
  5. Parking and utilities
  6. Permits, fees and timeline
  7. Permit-ready casita plans
  8. Casita Incentives Pilot: forgivable loans
  9. HOAs, deed restrictions and historic districts
  10. Renting it out and short-term rentals
  11. Permit steps
  12. Pre-approved plans
  13. Who to call
  14. Questions people ask

What you can build in San Antonio

The city's ADU page says ADUs are allowed in the R-1, R-2, R-3, R-4, R-5, R-6, RM-4, RM-5 and RM-6 districts, and in multifamily districts up to a total of five units. Only one ADU is allowed per property. It can be attached to the house (such as a garage apartment or in-law suite) or detached (a backyard casita). There is no limit on the number of bedrooms.

The rules are in Section 35-371 of the Unified Development Code (UDC). Check your zoning on the city's OneStop map.

Texas has no statewide ADU law, so the UDC governs. See our Texas ADU guide and what is an ADU. [1][2][5]

Size, height and setbacks

The UDC says an ADU "shall not exceed eight hundred (800) square feet or fifty (50) percent of the gross floor area (excluding covered porches) of the primary structure up to a maximum of sixteen hundred (1,600) square feet." The city reads this as whichever is larger: every property can have an ADU of at least 800 sq ft, and none can exceed 1,600 sq ft. The limit applies to attached and detached ADUs and counts only living area. The UDC sets a lower cap of 1,200 sq ft in the "RE" district.

For a detached ADU:

An attached ADU must meet the setbacks of the main house under the base zoning, and the zoning district's height limit. [1][2][6]

Owner occupancy

San Antonio requires the owner to live on the property. Under the UDC, the owner "must occupy either the principal unit or the accessory dwelling as their permanent residence, and shall at no time receive rent for the owner-occupied unit." Proof can be voter registration, vehicle registration or similar.

You sign a notarized affidavit and record a covenant with the Bexar County Clerk that tells future owners about this rule. The city's Information Bulletin 402 includes the application, affidavit and sample covenant. The county clerk's records office is at 101 W. Nueva St., Suite 103; call 210-335-2581 for hours and recording fees.

The city says a property where the owner does not live on site must be rezoned to allow more than one dwelling unit. [1][2][6]

Parking and utilities

Only a detached ADU larger than 800 sq ft needs one off-street parking space.

You can share the main house's utility meters or set up separate ones. If you want separate meters, the ADU needs its own address; request one with the city's address assignment form. If it shares a meter, it uses the main house's address. [1][2][6][7]

Permits, fees and timeline

You apply for a Residential Building Permit through the BuildSA portal and select an Accessory Dwelling Unit permit. It is a combination permit that includes the mechanical, plumbing and electrical inspections, so you don't pull separate trade permits. Include the recorded affidavit and proof of residency.

Besides permit-ready plans, you submit a site plan, a foundation plan, an energy report under the adopted energy code, and HVAC sizing calculations (Manual J) and equipment list (Manual S). The city says you don't need an architect for casita plans, but an engineer must approve and certify the foundation plans.

The plan review fee is invoiced first. Once you pay, initial review "can take up to three business days" for redline comments. After approval you pay the separate permit fees and the permit is issued. When all inspections pass, the city issues a Certificate of Occupancy. The city says total construction averages 3 to 9 months. See our ADU permit process guide and ADU cost guide. [1][6][7]

Permit-ready casita plans

The city's Casita Permit-Ready Plan Library has designs "reviewed and approved by the City's Development Services Department." They range from 375 to 800 sq ft. The plans are not site specific.

Base plans with no changes cost $450, paid directly to the designer. Site-specific or customized plans cost more depending on the designer. The city prefers that you apply for a building permit within 6 months of getting the plan. See our prefab ADU guide for other ways to save on design. [3]

Casita Incentives Pilot: forgivable loans

The Casita Incentives Pilot Program offers a no-interest, forgivable loan to build or rehab a casita, paid as reimbursement when the casita is done:

Approved pilot applicants who earn 80% AMI or less can also get up to $4,500 back for design fees when they use permit-ready plans. The property must be owner-occupied, and casitas used as short-term rentals don't qualify. If you have an HOA, you need its letter confirming a casita may be built. As of October 2026 the city's page showed the application as open.

The city's ADU page also mentions fee waivers for ADUs rented to lower-income households. The city's Fee Waiver Program page says its Affordable Housing category is closed after a January 2 to February 13, 2026 application window, so ask the Casita Program which waivers are open. More options are in our ADU financing guide. [1][4][8]

HOAs, deed restrictions and historic districts

The city will issue permits for casitas that meet its rules, but it "strongly" recommends checking whether HOA rules or deed restrictions prohibit them. The ADU application form asks whether deed restrictions would prohibit an accessory dwelling.

Casitas are possible in historic districts, but you need a Certificate of Appropriateness before the permit is issued. [6][7]

Renting it out and short-term rentals

You can rent the ADU or the main house, but not the unit you live in. An ADU used as a short-term rental (under 30 consecutive days) must follow UDC Section 35-374.01.

Under that section, on a non-multifamily lot, one non-owner-occupied unit on the same parcel as an owner-occupied unit counts as a "Type 1" short-term rental. Short-term rentals can't host weddings, events or restaurants in residential districts. [2][9]

Permit steps in San Antonio

  1. Check zoning and private restrictions

    Look up your zoning on the OneStop map and check HOA rules and deed restrictions. [1][7]

  2. Get plans

    Use a permit-ready casita plan or your own plans, plus a site plan, engineer-certified foundation plan, energy report and HVAC calculations. [1][3][7]

  3. Sign and record the owner-occupancy affidavit and covenant

    Have the affidavit notarized and record it with the Bexar County Clerk. Forms are in IB 402. [2][6]

  4. Apply in BuildSA

    Submit a Residential Building Permit Application in BuildSA, select the ADU permit, and attach proof of residency and the recorded affidavit. [1][6]

  5. Pay fees and answer review comments

    Pay the invoiced plan review fee; first comments come within about three business days. After approval, pay the permit fees and the permit is issued. [1]

  6. Build, pass inspections and get the Certificate of Occupancy

    The combination permit covers trade inspections. Once all pass, the city issues a Certificate of Occupancy and the ADU can be occupied. [1][6]

Pre-approved and sample plans

Who to call

Questions people ask

How big can a casita or ADU be in San Antonio?

Up to 800 sq ft or 50% of the main house, whichever is larger, with a cap of 1,600 sq ft. Every property allowed an ADU can have one of at least 800 sq ft. [1][2]

Do I have to live on the property?

Yes. The owner must live in the main house or the ADU, sign a notarized affidavit and record a covenant with Bexar County. Without owner occupancy, the property would need rezoning to allow more than one unit. [1][2][6]

Does a San Antonio ADU need parking?

Only a detached ADU over 800 sq ft needs one off-street space. [1][2]

How close to the property line can I build?

A detached ADU needs 5 feet from side and rear lines, or 3 feet with no overhang. Within 5 feet it must be fire rated. An attached ADU follows the main house's setbacks. [1][2]

Does the city help pay for a casita?

Income-eligible owners, or owners renting to income-eligible tenants, can get a forgivable loan of up to $25,000 or $35,000 through the Casita Incentives Pilot, Approved applicants earning 80% AMI or less can also get up to $4,500 back for permit-ready plan design fees. [4]

Can I Airbnb my casita in San Antonio?

Short-term rental of an ADU must follow UDC Section 35-374.01. Casitas used as short-term rentals can't get Casita Incentives funding. [2][4][9]

Sources (11)
  1. Accessory Dwelling Unit (ADU) Permits, City of San Antonio Development Services Department. Accessed October 9, 2026.
  2. Unified Development Code, Sec. 35-371. Accessory Dwellings, City of San Antonio (Municode). Accessed October 9, 2026.
  3. Casita Permit-Ready Plan Library, City of San Antonio Neighborhood and Housing Services Department. Accessed October 9, 2026.
  4. Casita Incentives Pilot Program, City of San Antonio Neighborhood and Housing Services Department. Accessed October 9, 2026.
  5. Bill History: SB 673, 89(R), Texas Legislature Online. Accessed October 9, 2026.
  6. Information Bulletin 402: Accessory Dwelling Units, City of San Antonio Development Services Department. Accessed October 9, 2026.
  7. Constructing a Casita, City of San Antonio Neighborhood and Housing Services Department. Accessed October 9, 2026.
  8. Fee Waiver Program, City of San Antonio Neighborhood and Housing Services Department. Accessed October 9, 2026.
  9. Unified Development Code, Sec. 35-374.01. Short Term Rentals, City of San Antonio (Municode). Accessed October 9, 2026.
  10. Development Services, City of San Antonio. Accessed October 9, 2026.
  11. Casita Program, City of San Antonio Neighborhood and Housing Services Department. Accessed October 9, 2026.

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