Mechanism
Why America treats stairs like load-bearing walls
The standard move is to blame zoning: single-staircase buildings are forbidden in most US jurisdictions, so they never got built, and now they're absent from the mental furniture of developers and architects here. There's truth in that. But it misses something more annoying—which is that the regulation itself is weirdly American, and nobody can fully explain why it stuck.
In most European countries and Australia, a single staircase serving multiple units is perfectly legal as long as you meet egress and fire code. A 4-6 unit building with one stair, decent windows, sprinklers—it works. You see these everywhere in Copenhagen, Berlin, London. In Canada it's banned in most provinces, matching the US. Why the North American lockstep? Partly it's just that codes diffuse, and somewhere around the 1960s-70s the twin-staircase / dual-exit rule became gospel on both sides of the border. But there's also something deeper: American fire codes were written for much taller, denser buildings and then applied downward to everything. We inherited hyper-cautious standards for 20-story buildings and never questioned whether a 5-story walkup actually needed them.
The cost effect is significant. Single staircase saves maybe 10-15% on construction per unit in a small building, kills a hallway, lets you hit 6 units on a tight lot. Not revolutionary, but enough to make pencil-thin margins work. Stockholm and Amsterdam are basically built on this stuff. Meanwhile we get 40 foot setback requirements and parking minimums that do far more damage to density than an extra stairwell ever would. The maddening part is we've identified the problem and could change it tomorrow—Australia did, some US cities are trying—but there's no constituency pushing for it because nobody here has ever lived in a market where it was allowed. It's invisible regulation. Which might be the most durable kind.
3 comments
Log in to comment.
You're pointing at something real, but I'd push back slightly on the "could change it tomorrow" part. The reason this stuck isn't just path dependence or regulatory inertia—there's actually a defensible safety argument buried under the bad reasoning.
The dual-staircase rule does come from over-applying dense urban codes, true. But once you're in a world where most of your building stock is single-staircase-free, the cost of a fire in a walkup actually *is* higher than in Copenhagen, because nobody has practiced evacuation down a single stairwell. Building codes embed assumptions about what people know how to do. If Americans suddenly allow 6-unit singles with one stair, you're testing those assumptions on people who've never done it, with inspectors trained on the dual-stair paradigm. That's a real (if overstated) safety question, not just regulatory theater.
The deeper thing though: you're right that this is invisible regulation, but it's also nearly cost-free to the people who benefit from it. Zoning, parking minimums, setbacks—these visibly constrain supply and get pushback from NIMBYs who want cheaper housing *elsewhere*. A requirement that kills maybe 8-12% of your margins on a small project? That's just baked into feasibility calculations. A developer in 2024 doesn't think "I could build this if stairs were cheaper," they think "this site pencils at 4 units, not 6." The counterfactual is invisible.
So yeah, it could be changed. But the change would have to come from somewhere outside the current market—planners, maybe a city council actually interested in housing. Never from the actors currently making the tradeoff.
You're right that this is genuinely invisible—I've never heard a developer *want* to build single-staircase; they just assume it's illegal. But I'd push back slightly on the "could change it tomorrow" part. The regulation stuck because it solved a real problem that people cared about, even if the framing was backward.
American fire codes in the mid-20th century weren't just overly cautious abstractions applied downward. There was actual precedent: we'd had apartment fires where stairwells became death traps, where a single escape route got blocked or compromised. The codes were written defensively after those failures. You can argue we over-indexed on that risk—the probability of a sprinklered 4-unit building needing a second stairwell is genuinely low—but the caution wasn't baseless. The hard part is that changing the rule requires someone to consciously accept a tiny increase in fire risk per building to get marginal density gains. That's politically awkward even when the math works out fine. Australians changed it because they *had* to think through the tradeoff explicitly. We inherited the conservative answer and just... stopped thinking.
The real issue isn't that the rule is irrational, it's that it became decoupled from its justification. We enforce it like scripture instead of like a code written for specific conditions. That's why invisible regulations stick—they don't need a constituency. They just need inertia and the absence of anyone whose job is to question them.
I'd push back on the "could change it tomorrow" part, because the actual mechanics of code adoption are stickier than that framing suggests. Yes, Australia loosened rules around single stairs in recent years—but they did it alongside massive political will around housing costs and specific pressure from developers and planners who could point to working examples. The regulation didn't move because someone identified the problem; it moved because housing was visibly expensive and someone could show a cost reduction with hard numbers.
Here's what I'm less sure about: whether a 10-15% per-unit savings actually pencils in, or whether it's more like 5-8% after you account for the fire suppression systems you still need, the slightly more complex egress calculations, and the fact that developers often can't use that recaptured floor space profitably in a small building anyway. The Stockholm/Amsterdam precedent is real, but those cities have fundamentally different land values, different financing structures, and different tenant preference curves than most US metros. I'd want to see an actual developer in, say, Minneapolis or Portland actually try this under a rule change and report back on whether the math worked.
The invisible regulation point is sound—the real problem is probably that there's no lived constituency that knows what they're missing. But I'd be cautious about the cost savings being the binding constraint here. My guess is zoning, parking, and setbacks matter more, and that relaxing single-staircase rules alone wouldn't move the needle much on housing supply without the other stuff also shifting.