Gretchen Whitmer signed two bills on the twenty-first of July that changed how many staircases a building in Michigan needs.
I know. Stay with me, because this is one of the more consequential things to happen to housing supply this year and almost nobody in our business has noticed it.
The rule
There is a line in the International Building Code, which is the rulebook nearly every state and city here starts from, saying that once a residential building goes above three storeys it needs two separate exit stairs, and you have to be able to reach both from anywhere on the floor.
Two staircases in a small building is not a detail. It is the building. On a narrow lot you need a corridor running the length of the floor to connect them, so the flats end up single-aspect, long and dark, with windows on one side only. Frequently the arithmetic simply does not work at all, and the lot stays empty.
That is why the corner site behind your local main street has been vacant for eleven years. Not zoning. Not the market. Stairs.
Culture shows up in your systems before it shows up in your values
That is a thing I say often enough that people at work have started saying it back to me, usually to win an argument.
A company will tell you it values speed and then you look at how a decision actually gets made and it needs four signatures. The values statement is aspirational. The system is the truth, because the system is what happens whether anybody is paying attention or not.
Countries are no different. We have spent a decade saying housing affordability is a crisis, and the code has quietly said the opposite the whole time, in a sentence nobody reads about staircases.
What it costs
Michigan's own figure is that the change could cut construction costs on middle-scale housing by upwards of ten percent.
Stephen Smith, who runs the Center for Building in North America, puts it as hundreds of thousands of dollars per building. On a small project, that is frequently the whole difference between a thing that gets financed and a thing that does not.
The buildings you get on the other side are also just better. One staircase means flats can have windows on more than one side, which means cross ventilation, daylight from two directions, and rooms a family can actually live in rather than a corridor with bedrooms off it.
It is not new, it is just not here
This is the part that surprised me most.
Seattle has allowed single-stair buildings up to six storeys since the 1970s. New York City has for decades. Honolulu legalised it in 2012. None of them are known for burning down.
Go further out and it gets odder. For all that the name suggests otherwise, that code is an American document. It does not underpin the rules in Britain, or Germany, or Japan. And plenty of those places post better fire outcomes than we do while cheerfully building four and five storeys on one stair.
So the rule is not the reason we are safe. It might just be the reason we are expensive.
Where it is actually moving
Seven states enacted single-staircase reform in 2025. Two worth knowing properly:
Colorado went first, in May 2025. Five storeys on one stair, though only in cities above a hundred thousand people. They had tried and failed the year before.
Michigan is the fresh one. Whitmer's two bills push the ceiling from three storeys to four, and separately open it up below six storeys wherever the local fire service is accredited.
The honest objection
I am not going to pretend this is settled, because it is not.
California's State Fire Marshal put out a report in March telling everybody to slow down, on the grounds that a second way out matters most precisely when something has gone wrong in a way nobody planned for. Firefighters' associations have pushed back on these reforms everywhere, consistently, and they are not being daft about it. They are the ones who go in.
What Colorado did about it is the bit worth copying. They went round the houses first, properly, with fire marshals and builders and code officials, and came back with something like twenty amendments bolted on. Wider stairs. A cap of four flats to a floor. Alarms to the national standard. Sprinklers and materials untouched at full code.
That is not deregulation. It is a renegotiation, and it is why it passed.
So where does that leave us
I went and looked, because a national story is only interesting if you can find yourself in it. Here is the state of play across the four markets we work, and the short version is that all four are moving and not one of them has actually changed anything yet.
Pennsylvania and Philadelphia
Senator Sharif Street, whose district is in Philadelphia, filed a co-sponsorship memo in January 2026 for SR 348. It would have the Uniform Construction Code Review and Advisory Council put its technical advisory committee to work on a study and a report recommending how the code might be modified to permit a single exit stairway.
Read that carefully, because it matters. It is a study. Not a change. A previous attempt, HB 1988 from then-Representative Joshua Siegel back in 2024, did not pass.
And here is the structural bit that explains why this runs through Harrisburg rather than City Hall. Pennsylvania municipalities may amend the state construction code, but they may not drop below its minimums. So Philadelphia cannot simply decide to permit this the way Baltimore is attempting to. It has to come from the state.
Which is a shame, frankly, because Philadelphia is the single best argument for the reform in the country. It is a rowhouse city built on narrow lots. An enormous share of the fabric everybody loves about it could not be built today.
New Jersey
New Jersey came closer than anybody. Assembly Bill 4972, from Assemblyman Clinton Calabrese, was introduced in October 2024 and reported out of committee in February 2025. It would let a municipality pass its own ordinance permitting a single exit stairway in a Group R-2 residential building under six storeys, with the ground floor allowed to be non-residential if it is a nonhazardous use with its own entrance.
Today the state rule is the standard one: R-2 above three storeys, two exits.
Two honest caveats. First, that bill sat in the 2024 to 2025 session, and New Jersey bills die when a session ends. I could not confirm it has been reintroduced in the current session, so treat it as unfinished business rather than a thing that is coming. Second, even if it does pass, it is written as a local option. Trenton would be handing the decision to each municipality, one at a time.
Which means for South Jersey the useful question was never going to be what the state does. It is what Cherry Hill does, and what Collingswood does, and what your particular borough does.
Baltimore
Maryland went the study route at state level too, with HB 489 directing the Department of Labor to look at it and report back. But Baltimore City did not wait. City Council Bill 25-0062, introduced by Councilman Ryan Dorsey in May 2025, would allow buildings up to six storeys on a single staircase. It went to committee, got a hearing, and the vote was deferred while the fire code language was worked out.
That is further along than anywhere else in our corridor, and Baltimore can attempt it locally because Maryland's arrangement gives the city room that Pennsylvania's does not.
Wilmington
Nothing. I looked and found no Delaware bill or ordinance on this at all. If somebody knows different I would genuinely like to hear it, but as far as I can tell Delaware has not entered the conversation.
What this actually means for you
A product type comes back. The four-to-twelve unit building on a normal lot has been effectively illegal at any real scale for decades. In states that move, it becomes buildable again, and it is the exact stock that is missing from every market any of us work.
Small lots stop being dead. The awkward infill site nobody could make work is the site this change is for. If you know where those are in your patch, you know something worth knowing.
It reaches you slowly, and unevenly. A state code change is frequently permissive rather than mandatory, so local governments adopt it on their own timetable or not at all. Tennessee wrote it into the state code and left it to local governments to take up. Which means the useful question is not "has my state passed it," it is "has my city adopted it."
Go and ask a small builder. Not a large one. The people this unlocks are the ones doing four units on a single lot, and they will know whether it has actually landed where you work long before it turns up in any market report.
Any road up
Everybody in this industry has spent three years saying the answer to the inventory problem is building more, and then talking about zoning, interest rates and land as though those were the whole list.
Meanwhile one sentence about staircases has been quietly deciding what is legal to build on a small lot, and it is changing state by state, right now, with very little noise.
Go and find out where your state is. It is a fifteen minute job and hardly any agent in your market will have done it.