The reason that the 2 stairway regulation in over 18m height residential buildings has become the standard is the issue with a fire preventing passage to the single stairwell, resulting in inability to exit. It’s not fire but smoke that will kill and no apartment is that sealed.
In the presence of fumes remaining in the apartment is not optimal. Automatic fire doors to isolate would not be possible with a single stair. You would obstruct exit. So if you’re at the non stair end of a level you’re at a survival disadvantage. And the standards need to reflect disabled also.
Developers would love to revert to single stair. The apartments would be slightly cheaper. But is the cost saving worth it?
I also note that sprinkler systems are mandated in the US generally above 75 feet. So these systems would not be currently installed in the 4-6 storey apartment building. It would be an additional cost.
Are you using AI to respond to me? Because what you are saying is not accurate
There may be some jurisdictions where this is the case but it's certainly not the case in the vast majority of the country. I'm curious where you got the 75 foot minimum idea? Whatever source told you that, you should probably discount its likely accuracy going forward.
In single egress buildings, unit entrances are directly onto the stairway — there is no "non-stair end of a level". Egress for a disabled person isn't any different.
Ah see you're talking about over 18 meters, in the US it's not allowed for over 3 stories I think. In Canada over 2 stories. In the US we just want to get to "single stair up to 18 meters".
In most states of the US it’s either 4 or 6 storeys - about half are at the 6 storey (or 18m) level.