How many units can you build in Austin? ADUs after HOME

Last verified August 5, 2026 against the Austin Land Development Code · KiliGray Homes

Up to three dwelling units are permitted on SF-1, SF-2 and SF-3 lots. Austin no longer has an "accessory dwelling unit" category — HOME repealed the accessory apartment and two-family sections, so a second or third unit is governed by §25-2-773 with its own standards.

Applies to: SF-1, SF-2 and SF-3 zoned lots. Small lots under 5,750 sq ft are limited to one unit under §25-2-779. The FAR gradient and Subchapter F carve-out only apply inside the Subchapter F boundary.

Austin does not have "ADUs" any more

This is the single most important thing to know, and almost every published Austin ADU guide still gets it wrong.

HOME Phase 1 repealed §25-2-901 (Accessory Apartments) outright and struck the accessory apartment from the list of permitted accessory uses. It also repealed §25-2-774 (Two-Family Residential Use) — the consolidated code now shows that section as RESERVED with an editor's note recording the repeal.

In their place: Duplex, Two-Unit and Three-Unit Residential Uses, all governed by a single section, §25-2-773, and all permitted in SF-1, SF-2 and SF-3.

So the question is no longer "can I add an ADU?" It is "how many units am I building?" — and the answer changes your setbacks, your floor area, your height and whether the McMansion ordinance reaches you at all.

	One unit	Two units	Three units
Permitted in SF-1/2/3	Yes	Yes	Yes
Minimum lot area	5,750 sq ft (1,800 on a small lot)	5,750 sq ft	5,750 sq ft
Governed by	Subchapter F	§25-2-773	§25-2-773
Subchapter F applies?	Yes (inside the boundary)	No	No
Height	32 ft inside the boundary	35 ft	35 ft
Front setback	25 ft or block average	15 ft	15 ft
Site floor area	0.4 or 2,300 sq ft	0.55 or 3,200	0.65 or 4,350

Going from one unit to two changes almost every number on the page — and removes Subchapter F entirely. See the individual pages for the detail.

The §25-2-773 standards

§25-2-773(A) opens by stating that the section supersedes the base zoning district regulations to the extent of conflict — so where it speaks, it wins.

Minimum lot area 5,750 sq ft. This is the hard floor. A lot under 5,750 sq ft cannot take two or three units — it is a small lot and limited to one.
Front setback 15 ft, down from 25.
Rear setback is the base district minimum, or five feet if the lot backs an alley or a lot zoned multifamily or less restrictive.
Building coverage 40%, impervious cover 45% — and front-yard impervious cover capped separately at 40%.
At least one street-facing entrance.

Full detail on setbacks, impervious cover and floor area.

Keeping the existing house can take it out of the floor area count

This is the most valuable provision in §25-2-773 and the least discussed.

If you preserve an existing dwelling unit, its preserved square footage can be excluded from gross floor area altogether — so the old house effectively stops competing with the new units for your allowance. Two routes:

Built on or before 31 December 1960 — preserve at least 50% of the existing dwelling unit and 100% of the street-facing façade.
Built on or after 1 January 1961 and at least 20 years old — preserve at least 50% of the existing dwelling unit.

The pre-1961 route carries limits on how you may alter the structure, keyed to roof form: on a side-gabled, cross-gabled, hipped or pyramidal roof, alterations are confined behind the existing ridgeline; on a front-gabled, shed or flat roof, to the lesser of 15 feet from the front façade or half the width of the front wall.

Separately, preserving an existing unit raises the three-unit any-two-units floor area sub-cap from 0.55 to 0.65 — a 2025 amendment.

Three other things HOME changed

Occupancy limits are gone. §25-2-511 (Dwelling Unit Occupancy Limit) was repealed. Austin no longer restricts the number of unrelated adults who may live in a dwelling unit — a rule that had stood for decades.

Tiny homes are defined. §25-1-21 now defines a TINY HOME as a dwelling unit of 400 square feet or less in floor area, excluding loft space. The loft exclusion is doing real work in that sentence.

The short-term rental restriction HOME added is gone. §25-2-773(D) originally barred one unit of a duplex or two-unit project from being short-term rented more than 30 days a year. The consolidated code now shows that subsection as Reserved.

It was not simply deleted — short-term rental regulation was restructured in 2025. Ordinance 20250227-039 made STRs an accessory use across all zoning districts, and 20250227-040 moved most STR regulation out of Title 25 into Title 4 (Business Regulation), with further operator and spacing limits added in September 2025. So the rules still exist; they are no longer in the land development code. We have not read Title 4 and do not cover STR licensing here.

The old size caps do not apply any more. If you read that an Austin ADU is limited to 1,100 sq ft or 15% of lot area, that came from the repealed accessory apartment rules. Under §25-2-773 the constraint is the floor area gradient across the whole site — 0.55 or 3,200 sq ft for two units, 0.65 or 4,350 for three — with a per-unit cap of 0.4 or 2,300 sq ft. Owner-occupancy requirements are gone too.

What actually decides it

The 5,750 sq ft minimum is the gate. Below that you are building one unit on a small lot, whatever you had in mind — and a great many Central Austin lots sit just under it.

Above it, the interesting question is whether to keep the existing house. The preservation route can be worth more than it looks: the old structure stops consuming floor area, and on a three-unit project it lifts the two-unit sub-cap as well. Against that, you are committing to work around an existing foundation and roofline, which is rarely the cheapest way to build.

We run both versions before advising. The answer turns on the condition of the existing house more often than on the code.

Common questions

How many units can I build on an SF-3 lot in Austin?

Up to three, if the lot is at least 5,750 sq ft. Duplex, two-unit and three-unit residential uses are all permitted in SF-1, SF-2 and SF-3.

Can I still build an ADU in Austin?

You can build a second or third dwelling unit, but not under the old rules — HOME repealed §25-2-901 (Accessory Apartments). What used to be an ADU is now simply a unit under §25-2-773, with its own setbacks, coverage and floor area.

Is there still a 1,100 sq ft limit on Austin ADUs?

No. That came from the repealed accessory apartment rules. The constraint now is the site-wide floor area gradient — 0.55 or 3,200 sq ft for two units, 0.65 or 4,350 for three — with any single unit capped at 0.4 or 2,300 sq ft.

Do I have to live on the property to build a second unit?

No. The owner-occupancy requirement was part of the repealed accessory apartment framework and does not appear in §25-2-773.

What is the minimum lot size for two or three units in Austin?

5,750 sq ft. §25-2-773(B)(1) sets that as the minimum lot area for duplex, two-unit and three-unit residential uses. Smaller lots are limited to one unit.

Can I short-term rent a unit in an Austin duplex?

The 30-day restriction HOME added at §25-2-773(D) is now Reserved. Short-term rental regulation moved out of Title 25 into Title 4 in 2025, with operator and spacing limits added that September. Check the current Title 4 rules — this page does not cover them.

Does keeping the existing house help?

It can, substantially. Preserved square footage of a qualifying existing dwelling unit can be excluded from gross floor area, and on a three-unit project preservation also raises the any-two-units floor area sub-cap from 0.55 to 0.65.

What counts as a tiny home in Austin?

A dwelling unit of 400 square feet or less in floor area, excluding loft space, under the §25-1-21 definition added by HOME Phase 1.

Working out what you can build?

We build in Central Austin and deal with this code on every project. If you own a lot and want a straight answer about what fits on it, we're happy to take a look.

Talk to us about your lot

We are homebuilders, not the City of Austin. This page explains how we read the code in practice — it is not legal advice and it is not an official determination. Always confirm with Austin Development Services before you rely on it for a project. The authoritative text is the Austin Land Development Code; permitting questions go to Austin Development Services Department.