What's Required in San Antonio
- ADUs are allowed in R-1 through R-6 and RM-4 through RM-6 districts, one per lot.
- The owner must live in the main house or the ADU and record a notarized affidavit and covenant in Bexar County.
- ADU size is up to 800 square feet or 50% of the main house, whichever is larger, never over 1,600 square feet.
- Detached ADUs sit in the rear yard, no taller than 25 feet or 2 stories.
- Detached ADUs need 5 feet from side and rear lines, or 3 feet with no overhang and fire-rated walls.
- ADUs over 800 square feet need one off-street parking space.
- Apply on BuildSA with the Residential Building Permit Application as a combination permit.
- Plans include a site plan, engineered foundation, framing, elevations, an energy report and Manual J and S.
Can you build an ADU in San Antonio?
Yes, by right in the R-1, R-2, R-3, R-4, R-5, R-6, RM-4, RM-5 and RM-6 districts, and in multi-family districts up to a total of five units, according to the Development Services Department (DSD). Only one ADU is allowed per lot. The catch is owner occupancy: under Unified Development Code Section 35-371(a)(1) the owner must live in either the main house or the ADU, sign an affidavit before a notary, and record a covenant in Bexar County's records that tells future owners the ADU depends on owner occupancy. If the owner will not live on site, the property must be rezoned to allow more than one dwelling unit.
How big can an ADU be?
DSD's ADU page sets the size at up to 800 square feet or 50% of the main house, whichever is larger, never more than 1,600 square feet, so every eligible lot can have at least 800 square feet. The rule applies to attached and detached units, there is no bedroom limit, and the ADU may share the main house's meters or have its own. A detached ADU goes in the rear yard, is limited to 2 stories and 25 feet, and may sit 3 feet from side and rear lines only with no eave within 3 feet of the line and fire-rated construction within 5 feet; at 5 feet neither applies. An ADU over 800 square feet needs one off-street parking space. In the RE district the code caps the ADU at 1,200 square feet.
How much does an ADU permit cost in San Antonio?
An ADU is filed as a combination Residential Building Permit, so the building, electrical, mechanical and plumbing fees are assessed together on one permit, by square footage, from DSD's FY 2027 Development Fee Schedule (revised September 2026). The schedule's Total Basic Permit Fees column adds the building permit, the trade permits, a $230.00 plan review and the $73.60 sewer fee:
| What you are doing | City filing | Rule |
|---|---|---|
| ADU up to 500 sq ft | Combination permit, $752.10 total | Building $172.50 + trades + plan review + sewer |
| ADU of 501–1,000 sq ft | Combination permit, $1,136.30 total | Building $488.80 row |
| ADU of 1,001–1,250 sq ft | Combination permit, $1,175.30 total | Building $517.50 row |
| ADU of 1,251–1,500 sq ft | Combination permit, $1,381.20 total | Building $718.80 row |
| ADU of 1,501–1,600 sq ft (the cap) | Combination permit, $1,603.20 total | Building $920.00 row |
| Main house or ADU rented at 80% AMI or below for 5 years | Fee waiver may apply | City fees and SAWS impact fees |
| Owner will not live on the property | Rezoning, not an ADU permit | UDC 35-371(a)(1) |
Worked example: an 800 square foot detached casita falls in the 501–1,000 row, $1,136.30, or $1,227.20 with the two 4% surcharges. The plan review portion is invoiced first and the rest after approval. SAWS water and wastewater impact fees are set by SAWS and are not part of this table.
How long does an ADU permit take?
DSD's fact sheet describes completeness review taking up to 3 business days, then a technical review that takes up to three business days for the first redline comments once the plan review fee is paid. You need permit-ready plans: site plan, engineered foundation plan, floor plan, framing details, elevations, an energy report under the adopted IECC, and Manual J and Manual S calculations for the HVAC. After inspections pass, DSD issues a Certificate of Occupancy and the ADU may be occupied.
How to Get a ADU Permit in San Antonio
Confirm zoning and eligibility
Check your district on the One Stop map and confirm you will live in the main house or the ADU.
Record the affidavit and covenant
Sign the owner-occupancy affidavit before a notary and record it with the covenant at the Bexar County Clerk.
Prepare permit-ready plans
Assemble the site plan, engineered foundation plan, floor plan, framing details, elevations, energy report and Manual J and S.
Apply and pay plan review
Submit the Residential Building Permit Application on BuildSA with proof of recording, then pay the invoiced plan review fee.
Build, inspect and get the C of O
Pay the remaining permit fees after approval, pass inspections, and receive the Certificate of Occupancy before anyone moves in.