SF-3 zoning in Austin: what Family Residence district allows

What SF-3 was for

The designation in §25-2-57 is precise about it: SF-3 is "the designation for a moderate density single-family residential use and a duplex use on a lot that is a minimum of 5,750 square feet."

The duplex is the whole reason SF-3 exists as a separate district from SF-2. Every dimensional standard is identical between them — the only thing that ever distinguished SF-3 was that it permitted two units where SF-2 permitted one.

HOME dissolved that distinction. Duplex, Two-Unit and Three-Unit Residential are now permitted uses in SF-1, SF-2 and SF-3 alike, all capped at three dwelling units per lot. The district that was defined by allowing duplexes is no longer distinguished by it.

The designation also notes SF-3 may be applied "to a use in an existing single-family neighborhood with moderate sized lots" — which is why it blankets so much of Central Austin's pre-war grid.

The five-foot rear setback for accessory buildings

Useful, and shared across the single-family districts — §25-2-553 (SF-1), §25-2-554 (SF-2) and §25-2-555(B) (SF-3) all carry the same sentence:

The rear yard setback is five feet for an accessory building that is not more than one story or 15 feet in height.

The base rear setback is ten feet. So a single-storey accessory structure — a garage, a workshop, a studio — may sit twice as close to the rear line as the main house.

Note the "or": not more than one storey or 15 feet. And note what it does not say — this is a setback provision, not a floor area one. The building still counts against floor area and impervious cover in the ordinary way, and if it is a garage the parking exemptions are a separate question.

It pairs well with the detached-rear-parking exemption, which wants the structure at least ten feet from the principal building — the two rules push a garage to the back of the lot from opposite directions.

55% impervious cover — rarely available, worth knowing

§25-2-556 lets the building official approve up to 55% impervious cover in SF-2 and SF-3, against the normal 45%. That is a large uplift, and the conditions are correspondingly narrow. All of them must hold:

• the principal use of the lot is residential;
• the lot is in a plat recorded before 2 January 1989;
• the lot adjoins open space — including a golf course or regional park — which must not contain, and must not be likely to be developed with, a significant amount of impervious cover; must contain at least twice the area of the adjacent lots; and must not be separated from the lot by an impervious barrier such as street pavement or a paved plaza;
• no setback variance has been granted or requested, and the owner agrees not to request one; and
• no development intensity transfer affecting the open space has been granted.

In practice this means a pre-1989 lot backing directly onto a golf course or regional park with no street between. Not many lots qualify — but if yours is one, ten percentage points of impervious cover on a 7,000 sq ft lot is 700 sq ft, which is a driveway and a patio.

The setback-variance condition is the trap. Requesting a variance forfeits it, and the owner has to agree not to request one in future — so the two reliefs are mutually exclusive and you have to choose early.

What sits on top of SF-3

The base numbers are a starting point. Three things routinely change them:

• Subchapter F — inside the boundary, one dwelling gets a 0.4 floor area cap, a 32-foot height limit instead of 35, and the setback planes.
• Building two or three units — takes you out of Subchapter F entirely and into §25-2-773, with 15-foot front setbacks and a higher floor area gradient.
• Overlays — a neighbourhood plan combining district can modify the maximum FAR, maximum gross floor area, gables and dormers at the setback plane, and the minimum front yard setback.

An SF-3 lot can also be subdivided below 5,750 sq ft under §25-2-779 — down to 1,800 — at which point a different regime again applies.