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Comment by amluto | Hacker News Reader

> The common hallway that must connect the two stairs in a modern American code-compliant building cuts the structure in two, cutting off the possibility of floor-through apartments found in traditional American multifamily architecture like the New York City tenement or the Los Angeles dingbat.

What requires a common hallway? The example single-stair plans seem like an equal number of staircases could be bolted on the back, giving every unit a second egress.

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> What requires a common hallway?

Effectively, the building code they are talking about the value of changing. Fully enclosed stairways at the back for each "slice" would be cost prohibitive, and exterior "fire escape" type stairs are not allowed either.

Even as a compromise you could make a pretty good small building with 2 units per floor, single walk-up stairwell+landing+elevator on the front, and an exterior fire-escape on the back.

This is a super common setup in my part of NYC (minus the elevator). It seems to work fairly well, especially since it makes it viable to have lots of buildings in a row with minimal wasted space between them.

It's definitely not the densest design possible, but it certainly seemed to let them fit a lot of fairly spacious 1-2 BRs in not a lot of space back in the early 20th c., and the height can scale up pretty well (though the elevator probably becomes at least a soft requirement above 4-5 floors).

I'm thinking more of a 10-floor building because I stayed in one with family in Buenos Aires that was like that several times.

The single-stair plan shown [1] isn't really single stair. It's three stairs, one per pair of units (per floor). If multifamily requires two means of egress, you'd need to add three more stairs, which takes up a lot of footprint. It would be easier to delete one stairway and add a hallway; but then only the two end units can address both the front and back of the building.

It's worse if you do stairs to a central landing and multiple units off that landing, where there's simply no way to add a single stairway that addresses all the units.

[1] https://substackcdn.com/image/fetch/f_auto,q_auto:good,fl_pr...

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