[Tiktaalik]

> The reason five over ones are popular in the US has nothing to do with staircase requirements. The reason is money, like always.

Yes it is money. More staircases remarkably increase the costs of buildings. Single stairway, cheaper buildings, more profitable to do other sorts of buildings, more variety of buildings etc.

(see also no parking mandates)

[bluGill]

Stairs are not expensivei they take space, but are cheay otherwise

[bell-cot]

By the time you've complied with all current codes, stairs themselves do take up an unreasonable amount of floor space.

But there's a usually-worse cost to the second set of stairs, that I'll call "geometry". A second set of stairs is not a giant support column, which you can wall off and ignore. The halls, doors, and such that it requires also suck up space, and impose many more restrictions on the layout of the actual living spaces for human beings - which are the sole reason for the building to exist.

[eru]

Space ain't free.

[FinnKuhn]

In most cities space is the expensive thing

[ethagknight]

At least in larger construction, it's the pathway to the secondary stair that takes up an exorbitant amount of space, hamstrings the layout. Also, code compliant fire egress stairwells are surprisingly expensive to build, costs more than the unit cost of a living space.