Do I also need a zoning permit for an ADU in Austin?

Residential review checks the unit count, floor-to-area limits and setbacks under the HOME amendments.

Where do I apply for a ADU permit in Austin?

Apply through Austin Build + Connect (AB+C), or call 311 (512-974-2000).

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.

Setbacks depend on your zoning district, and a flood zone can change the permit answer. Enter your address to see both.

Permit	When it applies
Building permit	A second or third unit is a new dwelling and needs a residential building permit.
Zoning review	Residential review checks the unit count, floor-to-area limits and setbacks under the HOME amendments.
Floodplain development permit	If the lot is in a FEMA special flood hazard area, all development there needs a permit.

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

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.

When does a ADU need a building permit in Austin?: A second or third unit is a new dwelling and needs a residential building permit.
Do I also need a zoning permit for an ADU in Austin?: Residential review checks the unit count, floor-to-area limits and setbacks under the HOME amendments.
Where do I apply for a ADU permit in Austin?: Apply through Austin Build + Connect (AB+C), or call 311 (512-974-2000).

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...