Mechanism
Single-staircase apartments are actually normal in most places
The standard North American take is that single staircase = fire code violation, which is why you see them everywhere else but almost nowhere here. Except that's not quite right, and the fact that we've convinced ourselves it is tells you something about how we regulate building.
Germany, the Netherlands, Japan, Australia—they all allow single staircase residential buildings routinely. Fire safety outcomes aren't worse. What's different is the code structure. In most of these countries, single staircase is permitted if you meet specific conditions: unit size cap, travel distance limits, sprinkler systems, fire-rated doors, sometimes a requirement that the stair connects to an exterior escape route or window. It's prescriptive but flexible. You're solving for the actual risk (occupants can't evacuate), not the solution (you must have two stairs). In the US and Canada, by contrast, our codes basically say two exits period, full stop, very little wiggle room. Some jurisdictions are slightly looser for buildings under a certain height or occupancy, but the default posture is prohibition rather than risk management.
Why does this matter beyond code nerd territory? Efficiency. A single staircase building (or a single stair + exterior escape) is cheaper to construct, takes up less floor area per unit, and fits on smaller lots. You get denser ground coverage without height penalties. This is part of why a mid-rise apartment building in Amsterdam or Berlin can pencil out on a narrower site than an equivalent North American project, even before you factor in land costs. We've structured our codes to essentially require a floor plan strategy that assumes abundant space.
The irritating part is that changing this wouldn't require safety theater or waiting for some catastrophe to prove it's safe—it's already proven. What it would require is re-writing codes to allow performance-based or risk-based alternatives, and that involves regulatory rewrite at the state/provincial level. Easier to just leave it as is, especially when developers aren't pushing hard (they've adapted to the two-stair constraint). So we keep building exactly as we always have, and then wonder why our residential buildings are so expensive and space-inefficient compared to peer countries.
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I think you're pointing at something real about prescriptive vs. performance-based codes, but I'd separate two things that often get tangled together here.
The actual fire safety question is narrower than it might seem. Single staircase buildings *do* work in those countries, but they work because of the bundle of conditions you listed—sprinklers, travel distance caps, fire-rated doors, often exterior windows. You're not really comparing "single staircase" to "double staircase." You're comparing "single staircase + active fire suppression + passive compartmentalization" to "double staircase + maybe some sprinklers." The stair count matters less than the full system. The Netherlands' research on this (there's some decent work from their building research council in the 2000s) shows that once you control for the other variables, the stair redundancy itself is doing less work than the code narrative suggests.
The harder part is that our codes often *won't let you prove* the alternatives work, which is different from saying they don't. Some jurisdictions technically allow performance-based design but the liability and approval timeline make it prohibitively expensive for a small developer, so it functions as prohibition anyway. Actually changing this would require regulators to stomach some genuine uncertainty about edge cases—what happens if the sprinkler system fails *and* there's a door wedge *and* someone panics—rather than just outsourcing the decision to "two exits, no conversation." That's a governance problem as much as a technical one, and I'm not sure how you solve it without a lot of political capital.
I spent two years trying to get a mid-rise project approved in a mid-Atlantic city, and I watched this play out in real time. The local AHJ (authority having jurisdiction) kept pushing back on our single-staircase design despite us citing Dutch and German precedent. Their response wasn't "we disagree with the safety analysis"—it was "that's not how our code is written." When I asked if we could do a performance-based equivalency, they basically said they don't have the staff to review that kind of submission, so we'd need to hire a consultant to argue it, which would cost more than just adding the second stair.
So we added the stair. What's maddening is that the second stair did nothing for actual fire risk in that building. We had sprinklers, enclosed stairs, travel distances well under code limits. The second stair was there because the default posture is "do what the code says literally" rather than "solve the actual problem." And yeah, this drives up costs in ways that compound—smaller units per floor, less flexible layouts, higher per-unit construction price. All of which ripples into rental rates or sale prices in markets where margins are already thin.
The code-rewrite piece is the hard part though. It's not that decision-makers don't believe the risk analysis. It's that performance-based review requires resources and expertise that a lot of jurisdictions simply don't have organized. So the path of least resistance is prescriptive requirements that are easy to check off. Not malicious, just structural.
I'd predict we don't actually change this, even though you're right that it's technically solvable. The barrier isn't epistemic—no one genuinely believes single-staircase buildings are less safe when they work fine in half the developed world. The barrier is that our code-writing process has become a maintenance operation for the status quo.
Here's what I've watched happen in criminal procedure: once a rule calcifies in enough jurisdictions, it stops needing justification. It just becomes "how we do things." Judges, prosecutors, defense lawyers—everyone learns the rule, builds their practice around it, and pretty soon you've got path dependency so deep that challenging it feels like you're asking people to rebuild their entire workflow. The actual safety argument becomes secondary. Someone proposes single-staircase and the first response isn't "let's look at the data," it's "but our code says two exits," which feels like evidence rather than assertion.
Add to that: state building codes are written by committees where the incumbent builders, code officials, and fire marshals all have seats, and they've all invested in knowing the current rules. A performance-based alternative means they have to actually evaluate risk on a case-by-case basis, which is more work and less legible—harder to defend later if something goes wrong. Prohibition is administratively simpler and politically safer, even if it costs everyone more. I'd expect maybe one or two progressive jurisdictions to move first (probably California or somewhere that's already been forced to reckon with housing costs), and then it stalls for a decade while everyone else says they're "monitoring the results."
I want to push back on the confidence here a little. Yes, those countries allow single staircase under conditions. But I'd be careful about the leap from "they allow it and haven't had worse outcomes" to "our codes are just conservative/space-wasting." Those aren't the same thing.
The conditions matter enormously and they're not small. Japan caps units per floor, sprinkler requirements are often mandatory, travel distances are strict, compartmentalization rules are tighter. You're not just removing a stair—you're implementing a whole different safety envelope. A real single-staircase equivalency test would be: take a building that meets German code requirements, transplant it to Portland, does it work? And the honest answer is it might, but you'd need to know which requirements are load-bearing and which are regional. I don't think anyone's actually done that legwork systematically in North America.
The efficiency argument is real but also easy to oversell. A second stair in a six-unit building costs real money and floor area. In a 40-unit mid-rise with mechanical systems anyway, it's absorbed differently. The sites where single staircase would unlock new projects are probably narrower than "all residential everywhere"—maybe certain lot shapes in certain markets.
On the regulatory rewrite part, yeah, that's the actual constraint. But "wouldn't require a catastrophe" assumes code bodies are purely rational and not also responding to liability exposure and liability insurance. That's harder to change than code text.