How many units can you build in Austin? ADUs after HOME
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HOME Phase 1 repealed §25-2-901 (Accessory Apartments) outright and struck the accessory apartment from the list of permitted accessory uses. It also repealed §25-2-774 (Two-Family Residential Use) — the consolidated code now shows that section as RESERVED with an editor's note recording the repeal.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.
Garage placement: which standard governs, and what it requires
Garage and carport placement is a separate design standard layered on top of the site development rules above. Which section governs turns on unit count and on whether the site sits in a Neighborhood Plan combining district that opted into garage placement standards — a Neighborhood Plan ordinance may apply §25-2-1604 to the district under §25-2-1406(6), but is not required to.
| Use type | NP area that adopted §25-2-1604 | Everywhere else |
|---|---|---|
| Duplex / two-unit | §25-2-1604 | §25-2-773(C)(3) |
| Three-unit | §25-2-773(C)(3) (NP status has no effect) | §25-2-773(C)(3) |
| Single-family, standard lot | §25-2-1604 | No garage placement standard applies |
| Small lot single-family (<5,750 sq ft) | §25-2-779(K)(3) (NP status has no effect) | §25-2-779(K)(3) |
A five-way conditional collapses to two variables: unit count, and whether the Neighborhood Plan opted in. Three-unit and small lot uses are governed the same way everywhere — Neighborhood Plan status never changes which section applies to them.
The §25-2-773(C)(3) rule for duplex, two-unit and three-unit uses
Outside an opted-in Neighborhood Plan, §25-2-773(C)(3) sets two limits, and they track the small-lot rule closely — see how "facing the front yard" is defined and how width is measured, which apply here too:
- A parking structure — garage or carport, attached or detached — may not sit closer to the front lot line than the front-most exterior wall of the first floor of the building façade.
- If its entrance faces the front yard and it sits less than 20 feet behind the façade, its width may not exceed the width of the building façade, measured parallel to the front lot line.
That 20-foot threshold is the duplex/two-unit/three-unit figure — the small-lot version of the same test uses 5 feet instead. Multiple parking structures serving one unit are totaled together, the same as on a small lot.
Duplex or attached three-unit width calculation. Where all garages face the front yard, the cumulative frontage of all garages is compared against the cumulative frontage of all units, not garage-by-garage against unit-by-unit. On a corner lot where the garages face different streets, only the garages that actually face the front yard are subject to the width requirement at all.
Through lots and multiple units on one site
A through lot — one with frontage on two streets, other than a corner lot — must comply with the applicable garage placement standard for any street frontage that provides vehicular access, not just the frontage the house faces.
For a site with more than one unit, every parking structure on the site must meet the applicable standard, and the application must clearly designate which unit each parking structure serves — a requirement that matters once a two- or three-unit site has more than one garage or carport to track.
What actually satisfies the street-facing entrance requirement
§25-2-773 requires at least one street-facing entrance per site. City staff interpretation CI2026-0002 (May 2026) defines the test in detail, because "facing the street" and "front door" both turn out to carry specific meanings:
- A qualifying entrance is either the primary door — the door that provides the primary entrance to the unit — or a porch that directly accesses the primary door and sits on the front façade, oriented toward the street.
- Side doors, garage doors, rear doors, courtyard doors and pool deck doors do not count as a primary door, no matter how prominent.
- On a corner lot, the primary door may face either abutting street. An alley does not count as a street for this purpose.
- A door "faces" the street if it is parallel or angled toward it — the same test used for garage placement above. It cannot be blocked from view by an enclosed part of the building, another building, or a garage, though an unenclosed decorative wall (a breeze block wall or screen) is allowed as part of the entrance design.
- A carport or porte cochère is never a qualifying porch.
Existing units get relief. An existing unit being preserved without façade modification does not need a street-facing entrance of its own — whether or not it qualifies for the preservation bonus below. If no unit on the site is visible from the street, none is required for the site at all; if any unit is visible, the site needs one. If an existing façade is being modified, that unit needs a qualifying entrance only if no other unit on the site can satisfy the requirement.
The front-yard porch allowance that rarely does anything
§25-2-773(C)(1) permits a porch to project into the front yard setback — but the same provision requires the porch to sit at least 15 feet from the front lot line. Because the front yard setback for these uses is also 15 feet, the two numbers are identical, and CI2026-0002 makes the point explicitly: the allowance does not actually let a porch encroach into the setback in practice. A porch roof or overhang gets slightly more room, at a 13-foot minimum from the front lot line.
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.
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
Send us an address and we will tell you what we find
We do this research ourselves on every project we take on — zoning, floodplain, watershed, trees, whether it is a legal lot. Send us an address and we will run it and tell you what we find. It works the same whether you own a vacant lot, a house you are thinking of adding a unit to, or a house you are thinking of replacing. No charge and no strings, and if it is a bad lot we will say so.
Send us an addressWe 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.