ADU rules in Austin, TX
Yes. A second or third unit is a new dwelling and needs a residential building permit.
Since the 2023 HOME amendments, SF-1, SF-2 and SF-3 lots can hold up to three homes.
Two-unit sites are capped at a floor-to-area ratio of 0.55 or 3,200 sq ft, whichever is greater.
Rules last checked by a person on October 19, 2026. Guidance only; confirm with Austin before you build.
Limits
| Units allowed | Up to 3 on SF-1, SF-2 and SF-3 lots (HOME Phase 1)Confidence: medium |
|---|---|
| Two-unit site size cap | Greater of 0.55 FAR or 3,200 sq ft |
| Any one new unit | Greater of 0.4 FAR or 2,300 sq ft |
| Three-unit site size cap | Greater of 0.65 FAR or 4,350 sq ft |
| Small lots (HOME Phase 2) | Single homes allowed on lots of 1,800 to 5,750 sq ft since Aug 16, 2024Confidence: medium |
Good to know
- Austin replaced the old accessory apartment rules with two- and three-unit residential uses. Setbacks follow the base zoning district; confirm them with residential review.
- Call 811 at least a few days before you dig footings or post holes. Utility locating is free.
- HOA covenants and deed restrictions can be stricter than city rules. Check yours before you build.
Check your lot
Where to apply
- Austin Build + Connect (AB+C)
- Work exempt from building permits
- City and Land Development Code
- Phone: 311 (512-974-2000)
Sources
- City of Austin, HOME Amendments. Checked 2026-10-19.
- Ordinance No. 20231207-001 (HOME Phase 1). Checked 2026-10-19.
The maximum floor-to-area ratio for the site is the greater of 0.55 or 3,200 square feet... a dwelling unit may not exceed the greater of 0.4 or 2,300 square feet.
- 44 CFR 59.1, definition of development (NFIP). Checked 2026-10-19.
Development means any man-made change to improved or unimproved real estate, including but not limited to buildings or other structures...
- 44 CFR 60.3, floodplain management criteria. Checked 2026-10-19.
Require permits for all proposed construction or other development in the community...