the single-stair floor plate

What a corridor-free plan does to unit count and daylight, now that SB 2835 has made it askable- and what four units per floor actually means for a narrow lot.

Austin already has one of these permitted. City Council passed the code change in April 2025, and by June the first three-story, single-stair building in the city had a permit- McKinney York's Ashram project, downtown. It's still under construction as I'm writing this, and the city hasn't published the count it promised when it passed the 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 its own law, SB 2835, which takes it statewide up to six stories. Austin's own cap stays tighter- five stories, four units a floor. And Austin isn't done moving on this- Council passed a resolution in March 2026 to build out actual "Missing Middle Residential" zoning categories that would put point access blocks on the same ladder as houseplexes, on lots as small as 5,750 square feet. 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.

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 hallway at all. One stair, one elevator, in the middle. Units wrap it on every side and every one gets light from two directions instead of one.

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.

Try it here: Single-stair floor plate study

Things considered were below, every lot is unique and additional items could result in varying iterations:

• 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