What counts as gross floor area in Austin?

Last verified August 10, 2026 against the Austin Land Development Code · Kimbrough Gray · KiliGray Homes

All enclosed space counts, regardless of its dimensions, unless it is exempted. The exemptions are parking, ground-floor porches, qualifying basements, qualifying attics, and any enclosed area five feet or less in height. Unenclosed space is outside the calculation entirely.

Applies to: Single-dwelling lots of 5,750 sq ft or larger inside the Subchapter F boundary. Small lots and multi-unit projects use a different gross floor area definition under §25-2-779(J) and §25-2-773(E).

One sentence, then the exemptions

The rule is simpler than most people expect, and simpler than it used to be. Until 2008 the code carried a list of things that counted and a list that did not. That structure was thrown out and replaced with a single test.

Is it enclosed? If yes, it counts — unless one of the exemptions reaches it. If no, it is outside the calculation entirely.

"Regardless of its dimensions" is doing real work in that sentence. There is no minimum size, no de minimis allowance, and no exception for oddly shaped space.

What the code says

In this Subchapter, GROSS FLOOR AREA means all enclosed space, regardless of its dimensions, that is not exempted under subsections 3.3.2, 3.3.3, or 3.3.4.

Austin Land Development Code · Read the full code

"Enclosed" is the whole test

Because the definition turns on enclosure, the practical consequences are cleaner than the old rule:

A carport does not count. Open sides, not enclosed.
A garage counts — then the parking exemptions in §3.3.2 may take some of it back out.
An open balcony or an uncovered deck does not count, at any story.
A mezzanine or loft counts, because it is enclosed space — not because the code names it. The 2008 amendment struck the sentence that used to name it explicitly.

The five-foot exemption people forget

§3.3.4 excludes any enclosed area five feet or less in height. On a house with a pitched roof that is a genuine amount of space — the low perimeter of an attic, storage tucked under a slope, the shallow end of a knee-wall.

The measurement is specified precisely, and the specificity matters. Height runs from the finished floor elevation up to the underside of the roof rafters, or to the bottom of the top chord of the roof truss. Explicitly not to collar ties, ceiling joists, or any furred-down ceiling. So dropping a ceiling does not create an exemption — the measurement looks past it to the structure.

Area is measured on the outside surface of the exterior walls.

The three exemption subsections

Everything enclosed counts unless one of these reaches it:

§3.3.2 — parking. Up to 450 sq ft for rear or open-sided parking, plus a conditional 200 sq ft.
§3.3.3 — porches, basements and attics. Each with its own conditions: ground-floor porches, below-grade space, and attics.
§3.3.4 — anything five feet or less in height.

§3.3.5 sits outside that list deliberately. It is not an exemption but a multiplier — see below.

Ceilings over 15 feet count twice

§3.3.5 is one sentence and it is expensive: an area with a ceiling height greater than 15 feet is counted twice.

A double-height living room, a dramatic entry, a vaulted great room — the floor area beneath it is charged to your allowance at 200%. On a lot working to the 2,300 sq ft minimum allowance, a 300 sq ft double-height space costs 600, a little over a quarter of everything you have.

Note where this sits. §3.3.1 defines gross floor area as enclosed space not exempted under 3.3.2, 3.3.3 or 3.3.4 — it does not mention 3.3.5, because 3.3.5 is not an exemption. It is a multiplier applied after the fact. Nothing about a tall room exempts it; the height simply makes it count double.

This is a design decision, not a code problem. But it needs making deliberately, early, and with the number in front of you.

A different definition applies to small lots and multi-unit projects

This page is Subchapter F. If you are building two or three units, or one dwelling on a lot under 5,750 sq ft, a different definition governs — and it is stricter in one specific way.

Under §25-2-773(E)(1)(b) and §25-2-779(J)(2), gross floor area is "the total enclosed area of all floors in a building with a clear height of more than six feet, measured to the outside surface of the exterior walls."

Note what is missing: there is no enumerated exemption list in those regimes — no §3.3.2 parking subsection, no §3.3.3 porch/basement/attic subsection, no §3.3.4 catch-all, carving specific space back out of a count that would otherwise include it. That is a real structural difference from Subchapter F. But it is not the same as "no relief," and treating it that way forfeits buildable area. The definition itself already excludes real categories of space before the question of an exemption ever arises: unenclosed space such as a porch or carport is not "enclosed" and never enters the count, and nothing with a clear height of six feet or less counts either — roughly parallel to the five-foot rule here, just drawn at a different line.

For duplex, two-unit and three-unit projects under §25-2-773, City staff interpretation CI2026-0002 (May 2026) spells out how that plays out for specific features: a porch that does not meet the code definition of "enclosed" does not count (one with glass windows does); an attic surrounded by roof assembly that is either inaccessible or reachable only by a pull-down stair or wall hatch does not count at any height; a staircase counts only on the floor where it originates; and a mezzanine or loft counts only for the portion above six feet. No comparable staff interpretation exists for small lots under §25-2-779 — the ordinance text sets the same six-foot threshold, but CI2026-0002's attic-geometry and porch rulings are scoped to §25-2-773 and are not established to extend there. The higher FAR ratios in both regimes were calibrated with this narrower baseline in mind.

Multistory features and elevators under §25-2-773

CI2026-0002 adds a general principle for any architectural space that spans more than one story of a duplex, two-unit or three-unit building: it is only counted on the floor where it originates. A handful of specific applications follow from that:

Elevators count toward gross floor area on every floor they access — the opposite of the general rule, because an elevator shaft occupies usable floor plate at each level it serves. The elevator penthouse is the exception: it is treated as an extension of the top floor the elevator services and does not count on its own.
Mechanical or utility shafts and structural voids that run continuously from the floor where they originate through another floor count only on the originating floor. If the space is interrupted by a floorplate — not continuous from one floor to the next — it is counted per floor instead.
Fireplaces and chimneys count only on the floor where they originate, regardless of how many floors they pass through.
Atriums and double-height spaces count once. A staircase with an adjacent double-height space is counted once for both the stair footprint and the adjacent atrium together. An enclosed staircase with no adjacent double-height space is different: only the stair footprint itself is counted once, and the standard-height space next to it counts on every floor it occupies.

None of this has an equivalent in the Subchapter F §3.3 exemption structure, which does not address multistory spaces as a category — Subchapter F's only comparable rule is the §3.3.5 double-count for ceilings over 15 feet, a different mechanism entirely. These rules are stated in CI2026-0002 for duplex, two-unit and three-unit projects under §25-2-773 and are not established for small lots under §25-2-779.

Splitting garage and accessory-space GFA between units under §25-2-773

A garage or accessory space counts the same way as anything else — enclosed, and above six feet, it is gross floor area. What is specific to duplex, two-unit and three-unit projects is whose allowance it draws against when more than one unit could plausibly share it. CI2026-0002 sets three rules, by configuration:

Attached to a single unit of a detached two- or three-unit project — its GFA is assigned entirely to that unit. It may not be shared with the others, even informally.
Attached to a structure with more than one unit (a duplex or an attached triplex) — its GFA is shared among the units in that structure by the ratio of each unit's size to the whole structure. The garage does not need to physically touch every unit it is shared with.
Fully detached — its GFA may be shared among all or any of the units. The one exception: if the detached space has its own utilities, its GFA is allocated to whichever unit shares a utility meter with it.

Where GFA is shared, the calculation excludes the shared space itself from the initial ratio, then applies that ratio to divide the shared space: each unit's share of the garage or accessory space equals its percentage of the combined GFA of the units sharing it. If only two of three units share a garage, the third unit is left out of the ratio entirely — it draws none of that GFA. CI2026-0002 requires the resulting percentage and square footage for each unit to be shown on the submittal plan set. The interpretation includes two worked diagrams (shared garage GFA between two units, and between three units) and a five-part exhibit of shared-garage configurations that this page does not reproduce.

How this plays out on a real lot

The enclosure test rewards a specific kind of design: covered outdoor space that stays open. A deep porch, a breezeway, a carport instead of a garage — none of it counts, and all of it is useful for most of the Austin year.

The mistake we see is enclosing something late in design for a practical reason — screening a porch, adding a garage door to a carport — without anyone re-running the floor area. That single change can move a project from compliant to over.

Common questions

Does a carport count toward floor area in Austin?

No. Gross floor area under Subchapter F is all ENCLOSED space not otherwise exempted. A carport is not enclosed, so it is outside the calculation before any exemption is even considered.

Does a garage count toward gross floor area?

Yes, it is enclosed and counts — but the §3.3.2 parking exemptions may remove up to 450 sq ft of it, and in some layouts a further 200 sq ft.

Does a second-floor balcony count toward floor area in Austin?

Not if it is unenclosed. The rule turns on enclosure, not on whether the space is covered. The 2006 provision that counted upper-story roofed areas was struck in 2008.

Does a loft count toward gross floor area?

Yes, if enclosed. It counts because it is enclosed space, not because the code names it — the sentence that used to name mezzanines and lofts was removed in 2008.

Do high ceilings count double toward FAR in Austin?

Yes, above 15 feet. §3.3.5 states that an area with a ceiling height greater than 15 feet is counted twice, so the floor beneath a double-height space is charged to your allowance at double.

Is there a minimum size before space counts?

No. The definition says "regardless of its dimensions". The only size-based relief is §3.3.4, which excludes enclosed area five feet or less in height.

How is shared garage floor area split between units in an Austin duplex or triplex?

It depends on the configuration. A garage attached to only one unit is charged entirely to that unit. A garage attached to a structure with more than one unit is split by the ratio of each unit's size to the whole structure. A fully detached garage can be shared among any of the units, except that a garage with its own utilities is assigned to whichever unit shares its meter.

Does an elevator count toward gross floor area on a duplex or three-unit project?

Yes, on every floor it serves — unlike stairs, which count only on the floor where they originate. The elevator penthouse is the exception: it counts as part of the top floor and is not charged separately.

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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.

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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.