educational estimating tool - not professional advice. every number here is a placeholder until verified. read the full disclaimer.

Austin · current code · September 2026

what a small lot yields with one stair instead of two

A parametric comparison of the two-stair rule against the point access block, on a lot too narrow for a double-loaded corridor. Change the numbers; the plans and the math follow.

Why this is not a speculative study. Since 1 September 2025, Texas law lets a city allow single-stair apartment buildings up to six stories — Local Government Code § 214.301, added by SB 2835. It is enabling legislation, not legalization: a municipality may authorize it, so the building is legal only where the city has adopted it. Austin has, at five stories, four dwelling units per floor, with a protected stairwell and sprinklers in the interior exit stairway to NFPA 13 — City Code § 25-12-3, Ord. 20250410-045, effective 10 July 2025. Where a city has not adopted it, a single-exit R-2 building is still capped at three stories.

One cap this page flags but does not enforce: Austin’s amendment also limits the net floor area of each floor served by a single exit to 4,000 square feet (§ 1006.3.4.2 item 1) — the single-exit card under code checks says when a plate is over it. The same section caps travel from a unit door to the stair at 20 feet and requires an elevator; neither is modeled. At four or five stories, a plate this page draws larger than 4,000 sf is not a permitted single-stair floor. Verify against the ordinance before putting any of this in front of a client.

Every default below is an assumption, not a fact. Setbacks, unit depths, core sizes and the circulation allowance are reasonable starting figures, not Austin code minimums checked line by line. The value of this page is that it makes the argument visible in about thirty seconds - it gets genuinely persuasive only once real numbers replace these. The exit-separation, dead-end, travel-distance, compatibility, fire-separation and utility-clearance figures below are checked against primary code sections (cited on each card) - a couple are flagged where the primary text couldn't be fully verified. Everything else on this page is still a planning-stage assumption. Built for Austin, Texas. Austin's own amendment sets the numbers here (five stories, four units a floor), inside the six-story ceiling Texas SB 2835 lets a city adopt; other states and cities are adopting single-stair rules on their own schedules with different limits. See the tools page for more on this.

inputs

Lot width (ft)street frontage

Lot depth (ft)front to rear

Side setback (ft)each side

Front setback (ft)

Rear setback (ft)

Corridor width (ft)scheme A only

StoriesAustin cap: 5

Units / floor (B)Austin cap: 4

Dist. to triggering lot (ft)SF-5 or stricter, 1-3 homes

the two floor plates, same lot

a · two stairs, single-loaded

What the old rule actually allows on a narrow lot

b · point access block

One protected stair, units on all sides of a central core

what the difference is worth

Per floor	A · two stairs	B · point access	Difference

code checks - the numbers behind the claims

read this before using any of it

The real argument is not "one stair is better than two." It is that on a lot this narrow a double-loaded corridor does not fit at all - the building is not deep enough to put units on both sides of a hall. So the honest comparison is against a single-loaded plate, which spends corridor on one row of units and still pays for two stairs. That is the plate being beaten here, and it is the plate that actually gets built.
Two exposures is the part that does not show up in a spreadsheet. Every unit in scheme B spans the full building depth, so it has windows front and back: cross-ventilation, light from two directions, and a corner in most cases. In scheme A every unit faces one way. The efficiency gain is the argument to a developer; the two exposures are the argument to a renter - and they are what makes it a better apartment rather than only a cheaper one. Be precise about which two sides deliver this. At a tight side setback, fire-separation rules cap side-wall glazing well below a full window wall (see Code checks below) - the real dual-aspect benefit is almost always front and rear, not the two narrow sides.
Fire response was the objection raised at Council, and it is not a bad-faith one. Know the sprinkler specification, the stairwell protection rating, and the travel-distance limit cold before presenting this anywhere. It will be the first question, and having a real answer is the difference between a study and an opinion.
The circulation allowance in scheme B is a simplification. A real point access block still needs a small elevator lobby and a landing at each level; here that is folded into the core figure. A real plan will land a few points below the number this page produces - which is fine, because it is still far above scheme A.