The Map Is Changing. Here's Every State Moving on Single-Stair Reform.

One hundred years ago this fall, the Supreme Court decided Euclid v. Ambler Realty and handed American cities the legal machinery to separate everything from everything else. Homes here, shops there, schools over there, workplaces over here — and you had to drive between all of them.

I bring up the anniversary because it frames the moment we're in. The regulatory order Euclid set in motion took decades to assemble. It's now being reformed in a meaningful way — and single-stair reform is one of the clearest places to watch it happen.

When I wrote about the 21st Century ROAD to Housing Act a few weeks ago, a lot of people responded with some version of the same question: "This is federal — but what's actually happening on the ground, in my state, right now?"

Fair question. The honest answer is: more than most people realize.

The federal bill is the headline. The real story is a state-by-state movement that's been building since 2022, gaining speed every year, and is now running well ahead of Washington D.C. As of late 2025, by the Pew Charitable Trusts' count, nineteen states and the District of Columbia had introduced bills to study or allow single-stair construction since 2022 — and seven states passed and signed legislation in 2025 alone. The 2026 sessions have already added more.

Here's where things actually stand.

The States That Have Already Done It

Washington has been the quiet pioneer since 2023 — the first state to reform its building code to allow single-stair apartments. It hasn't stopped since. In 2024 it extended residential code to middle housing. In 2026 it legalized smaller elevators and passed the first statewide scissor-stair reform in the country. If you want to see where American housing code is going, watch Washington.

Seattle has been doing this since the 1970s. The rest of the country just wasn't paying attention.

Tennessee deserves more credit than it usually gets. Back in 2024 — before most of the states on this list — Tennessee passed a law letting municipalities adopt a building code permitting single-stair buildings up to six stories. Knoxville adopted the provision in November 2024; Jackson followed in December. It was one of the earliest statewide enabling laws in the country, and it set the template — six-story ceiling, local opt-in — that several states would follow.

Colorado moved boldly in 2025, enacting a law in May that allows multifamily buildings up to five stories with a single staircase in municipalities over 100,000 people. Eight major cities — Denver, Colorado Springs, and Fort Collins among them — must update their local codes by December 1, 2027. A companion bill requires cities to allow housing on nonprofit, school, transit, and public-agency land even where it wasn't previously zoned for it.

What's notable about Colorado is that the political leadership embraced the reform as housing-affordability policy, not a design footnote — and it did so out loud, before the law passed. In early 2025, Governor Polis called for "Smart Stair" reform in his State of the State address, coining the name himself. In March he showed up to the Denver Single-Stair Housing Challenge Awards — an international design competition run by SAR+ Architects that drew 211 entries from 45 countries, reimagining the point-access block for Denver's context. Standing at the event, with the enabling bill still moving through the legislature, he put it plainly: "We know that Smart Stair buildings can take up less space, and they can cost less to build." He pointed to the then-new Pew study finding such buildings could cost nearly 13 percent less than their dual-stair equivalents. When a governor turns up at an architecture competition, brands the building type, and tells the room he's going to legalize it — the reform has arrived. The May law followed.

Montana passed what analysts are calling the strongest single-stair law in the country. It applies to every jurisdiction statewide, allows buildings up to six stories with modern fire-safety systems, and sets no population threshold. No carve-outs. No local opt-outs. Montana just did it.

Texas With SB 2835 — authored by Senator Nathan Johnson, enrolled in June 2025 and effective September 1 — Texas passed what's likely the first statewide six-story single-stair measure of its kind. It lets municipalities authorize apartment buildings up to six stories and four units per floor on a single staircase, capped at twenty-four units, even in cities that haven't adopted their own IBC amendments. It's an enabling law, so cities opt in — but the authority now runs statewide. Austin had already moved first, with a local ordinance in April 2025 allowing single-stair construction up to five stories.

The four-units-per-floor limit is the part that matters most, and it's worth pausing on, because it's the cleanest answer to the safety objection and the strongest argument for why developers should care. A double-loaded corridor — units lined up on both sides of a windowless interior hallway — exists because the second stair forces the building to be big enough to pay for itself. Strip out the second stair and the building can shrink, the corridor disappears, and every unit can sit on a corner with windows on multiple sides. The Texas Legislature's own statement of intent makes the point plainly: these buildings reach roughly 95 percent floor-plate efficiency, get better cross-ventilation and daylight, and can hold the extra bedrooms that make a unit work for a family rather than just a single renter. That's not a fire-safety concession. It's a better apartment. Texas now sits alongside Montana at the top tier of reform ambition.

New Hampshire passed legislation in 2025 allowing buildings up to four stories — a more conservative ceiling than Montana or Texas, but a real step for a state that has historically been cautious about code changes.

Oregon took a more tangled path. Legislation directed the Building Codes Structures Board to adopt a reform, but the outcome is a compromise: four stories with local opt-in, effective October 2025. The opt-in weakens it, but the reform exists.

Minnesota funded a $225,000 study in 2023 and got findings in late 2025. A technical advisory group has recommended a four-story limit, on track for the 2026 code update.

New York City has allowed single-stair buildings for decades — it's a big part of why the pre-war walkup exists at the scale it does across the five boroughs. The state is now catching up: a statewide single-stair study mandated by 2024 legislation is due in July 2026, and the findings are expected to open the door to statewide reform.

The States in Motion Right Now

California is the most complicated case — and the most consequential, given its size and its housing crisis.

The State Fire Marshal delivered its overdue report in March 2026, recommending a cap of just four stories — only one above the current limit — which advocates and architects immediately called inadequate. The report does leave a path for legislators who want to go higher, but it takes a dim view of the reform. AB 2252, from Assembly member Alex Lee, is still moving through the legislature; it targets four-plus stories with a single stair, and advocates are pushing for six. Meanwhile a statewide freeze on local building-code amendments through 2031 means cities can't act on their own anymore. Everything now runs through Sacramento.

A few cities did beat the clock. Culver City adopted a six-story single-stair ordinance modeled on Seattle's standards, just days before the October 2025 deadline. Santa Monica got one through as well. Los Angeles came close and then withdrew. The statewide picture is in flux, but the direction is clear. California will get there. The fight is over how tall.

Massachusetts held public hearings on single-stair study-commission bills in June 2026, with national experts testifying in support. Boston Indicators published research recommending single-stair buildings up to six stories with a maximum of four units per floor. Watch for committee action before year-end.

Virginia had a working group issue reform options in 2024 and then formed a follow-up group to draft actual code language. Reform is expected.

Idaho passed H.B. 706 (Rep. Jordan Redman) in spring 2026, signed in April — a local-option law letting cities permit single-stair buildings up to six stories. The ceiling is ambitious; the mechanism, like Texas and Oregon, is municipal opt-in. It passed narrowly and takes effect July 1, 2026.

Connecticut enacted legislation in 2025, with implementation details still being worked out.

Hawaii and Maryland convened study groups in 2025. Studies usually run 12 to 18 months, which puts both on a 2026–2027 timeline for possible code action.

Maine was finalizing single-stair legislation as of mid-2025.

Washington, D.C. introduced the "One Front Door Act" (B26-0227), which would allow single-stair buildings up to six stories in the District. It's in committee.

What the Map Tells Us

Step back and look at the whole picture, and a few things come into focus.

This is genuinely bipartisan. Montana, Texas, Tennessee, New Hampshire, and Idaho are not states you'd file under "housing reform." Colorado and Washington lean the other way. The coalition spans the full political spectrum because the argument isn't ideological — it's practical. More housing. Lower cost. Better buildings. That's a rare thing in American policy right now, and it's worth saying out loud.

The action is in the states, not the cities. This is the pattern that surprises people. We tend to assume cities lead on housing and states follow. Right now it's the reverse. As The Philadelphia Citizen observed in a piece on state housing legislation late last year, the cutting edge in zoning is happening in states, not cities, these days. That's exactly what the single-stair map shows — statewide laws in Montana and Washington reaching further than most municipal ordinances ever could.

The safety objection is losing ground. The consistent barrier has been fire-marshal opposition — the claim that two stairs are inherently safer than one. That argument is getting harder to hold. Across New York City and Seattle's modern single-stair buildings from 2012 to 2024, Pew found four fire-related deaths — and in none of them did the absence of a second stair play a role. Seattle has allowed these buildings since the 1970s. Modern sprinklers, smoke pressurization, and supervised alarms have changed the underlying calculus. Montana's law — the strongest in the country — required fire-safety systems but not a second stair, and it passed.

This is a movement now, not a theory. Stephen Smith, who runs the Single-Stair Tracker at the Center for Building in North America, has put his finger on what's different this time: grassroots energy of a kind the code world rarely sees. He describes the YIMBY movement getting interested in codes and standards in a way building-code decision-makers haven't encountered before — and a real culture clash as a result. That clash is the sound of a seventy-year consensus being renegotiated in public.

The height question is still being fought. States are landing at four, five, or six stories depending on their politics and their fire-marshal relationships. Six is the right target. It unlocks the most urban infill and matches the European precedent the reform is drawing on. Four — what California's Fire Marshal recommended — is too conservative to move the missing-middle market. This is a fight worth having in every state still working it out.

And the IRC argument is still underused. As I argued in my last piece, the most important question in this reform isn't only how tall the buildings can be. It's which code governs them. Several places — North Carolina, Dallas, Memphis — have moved small multifamily buildings under the IRC, the residential code, rather than the IBC, the commercial code. Dallas passed a unanimous ordinance in April 2025 allowing up to eight units under a modified IRC. That's the right framework. A small point-access block building has far more in common with a house than with a high-rise, and the code that governs it should say so. The federal rule making the ROAD Act sets in motion is the moment to make that case at national scale — not just to carve single-stair buildings out of the IBC, but to recognize that they belong in the IRC in the first place.

What This Means If You're Building Right Now

The patchwork is real, and it matters for feasibility. A building that's legal in Denver may be illegal one municipality over. A six-story single-stair building that pencils in Austin may not work in Dallas under the same state law. Federal HUD guidelines, when they land in 12 to 18 months, will start to resolve this — but until then, state and local code is the field you're playing on.

The practical read:

If you're in Washington, Montana, or Texas, the full reform is available now. These are the states to start piloting in.

If you're in Colorado, eight major cities must comply by December 2027 — which means the design conversations need to start now.

If you're in New York, the statewide study lands in July. Position with developers before the reform is official, not after.

If you're in California, watch AB 2252. The six-story threshold is the fight that matters. Four stories won't move the market.

If you're in a state that's not on this list yet — and there are still plenty — the federal bill hands your legislators cover, precedent, and the promise of grant funding. The window for state advocacy is open right now.

The map is changing, faster than most people realize, and from directions nobody would have predicted ten years ago. A century after Euclid gave us the tools to take these buildings apart, we're finally assembling the tools to build them again. The question for architects, developers, and cities isn't whether the reform is coming. It's whether we'll be ready to build well when it arrives.

I'm an architect focused on traditional neighborhood design, new urbanism, and building code reform. If you're working on a project in one of these states and want to talk through what the reform means for your building type or your site — reach out.

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