Evidence
Single stairs make housing denser, so why did we ban them
I kept noticing this while reading building codes across different countries, and it finally clicked why it matters. In Stockholm, Berlin, London, you see five-to-eight story residential blocks with one staircase serving four or six units per floor. The hallway is narrow. There's an elevator (sometimes). The fire safety is solved through distance-to-exit rules and materials standards, not redundancy. Meanwhile, in the US, anything over three stories with more than a handful of units needs two egress stairs minimum. We've basically coded ourselves into a particular geometry.
Here's where I'm cautious: I don't actually know if we could just copy their rules and get the same safety outcomes. The US versions of this code—IBC language about "means of egress" and travel distance—came from somewhere, even if the reasoning is now lost under layers of precedent. But I do know that Paris, Amsterdam, and Toronto have had fewer residential fires per capita than comparable US cities over the last two decades, and they're doing this with single-stair buildings legally everywhere. So either their approach works or they're getting lucky in ways that scale.
The real cost is housing form. Two egress stairs means a wider building footprint, or deeper lots, or more vertical circulation eating into rentable space. In Tokyo or Copenhagen, you get more units on a smaller footprint because you're not forced to waste volume on redundant stairs. And because you can fit more units, the per-unit land cost drops, which matters more for rent than anything else we talk about. I've seen some proposals to let single stairs in mixed-use or retrofit buildings under 55 feet, but we haven't actually changed the baseline rule in most states. That's not a safety insight—that's a choice.
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The fire safety part actually deserves more scrutiny here, because the comparison gets slippery fast. Those European cities you mention do allow single stairs, but they're not doing it under identical conditions to US buildings. Stockholm and Berlin have much stricter material codes (non-combustible construction requirements that are way more onerous than US prescriptive paths), narrower travel distances baked into the geometry itself, and different occupant behavior—smaller units, often owner-occupied rather than rental churn, denser street presence that means faster external response. When researchers have looked at actual fire outcomes, it's genuinely hard to untangle whether the single staircase is safe *because* of what surrounds it or whether it would work the same way transplanted into, say, a sprawling suburban-density US context.
That said, your point about the coding-as-choice part is solid and separable from the safety question. Even if we concluded "yes, single stairs require all these other conditions to work safely," we could still be choosing to require those conditions instead of requiring two stairs. We're not. We're requiring the redundancy *and* often not requiring the material standards or density that make the alternative viable. It's like saying we'll only permit the safe version of the risky option, then not actually implementing the safe version.
The real move would be to run a controlled loosening in one or two states—maybe mixed-use buildings under 65 feet with non-combustible structure and explicit travel distance limits—and actually measure outcomes instead of staying paralyzed between "it works in Copenhagen" and "but is it American enough." We won't do that, though. Easier to keep the rule.
I'd predict we don't change this substantially in the next fifteen years, even as housing costs keep rising. Not because the safety case is weak—it probably isn't—but because the people who'd have to reverse the rule have zero incentive to absorb the political cost if anything goes wrong.
Here's the thing: a fire in a single-stair building kills five people instead of three, even if it's statistically no more common than fires in comparable dual-stair buildings, and suddenly you've got a lawsuit, local news, and a city council member who "relaxed fire codes to pad developer profits." The asymmetry in blame is total. Nobody gets credit for the three hundred units of housing that costs 15% less to build. The fire gets the headline.
What might actually move it: not safety data but liability isolation. If a city could write an exemption that applies only to buildings where the developer carries a specific insurance policy, or where the property owner signs away some class action right, or where it's limited to buildings under a certain height in certain zones—something that lets decision-makers point at a third party and say "they absorbed the risk"—then maybe. That's how you get change in systems where plausible deniability matters more than outcomes. But I'm not holding my breath.