the single-stair floor plate

The idea is simple once you say it out loud- collapse the double-loaded corridor and every apartment can be the width of the apartment. A narrow lot that could never fit units on both sides of a hallway stops needing the long hallway, just a short rated corridor to the stair- that's what four units a floor actually means for a narrow lot. One stair, one elevator, in the middle. Units wrap it on every side and every one gets light from two directions instead of one.

Austin already has one of these. McKinney York's Ashram, downtown, was permitted in March 2022 under the city's earlier three-story allowance, and the city's permit record shows it finished in October 2024. Council then raised the limit to five stories in April 2025, and the city hasn't yet published the yearly count council ordered when it passed that ordinance- how many have actually been permitted since. So I'm not going to make up a number. One real building is still one real building, and that's more than a thought experiment.

Texas followed a few months later with SB 2835, which lets any city allow single-stair buildings up to six stories if the city opts in. Austin's own cap stays tighter- five stories, four units a floor. And Austin isn't done moving on this- in March 2026 Council told the city manager to draft new missing-middle zoning districts, townhomes, cottage courts, single-stair buildings and small multi-unit buildings, with the number of units tied to lot size. Staff's January study suggested a 5,750 square foot minimum lot for the house-scale zones, but that's a recommendation, not something Council has adopted. That's still in process, not finished. Dallas did its own separate thing too- a different ordinance, capped at three stories, not tied to the state law at all. Worth knowing the difference if either comes up.

I built a tool that runs the numbers on this- lot width, depth, setbacks, all of it- and draws both floor plates side by side so you can see what you're actually trading. It's not a construction document. It's meant to make the argument visible in about thirty seconds, then get better once real numbers replace the defaults.

Two things kept showing up when I ran it. The price came down when I reallocated the square footage from the double loaded corridor (a rated assembly) and eliminated a staircase. That helps the financials of missing middle, and price points are one of the biggest reasons we need missing middle in the first place. And when the stair and corridor went back to the units, the usable floor area went up- how much depends on the lot, and the tool shows it for yours. Obviously if you put a bathroom, or some other function that is expensive by the square foot, into that space it can push the cost way up. But if it expands bedrooms or living areas, there was good evidence this is a great move in rentable or sellable square footage.

what the tool checks- every lot is different, and other items can change the answer:

• exit separation
• dead-end corridor length
• exit access travel distance
• compatibility height limits near single-family-zoned lots
• fire-separation distance and window percentage
• Austin Energy clearance from overhead lines and equipment