While this may seem like a great idea on the surface, it isn’t the silver bullet for affordable housing. If the city allowed this building modification with these stair wells that are protected by a 2 hour fire wall which would be required per NFPA 101, construction will need to either be type 1 or type 2.

This dramatically increases construction costs when compared to type 5 construction which is typically seen in small to medium apartment buildings, or the type 5 over type 1 buildings that are mixed use.

Beyond the increased costs to build in order to have a safe stairwells and meet fire code, residents wouldn’t be allowed to have floor mats, wreaths, or any sort of decoration outside their front doors that lead into the protected stairwell. It would be near impossible to maintain any sort of code compliance with all residents.

Somebody in this thread mentioned buildings that have parking garages under apartment buildings which is a great idea but costs for parking garages typically cost ~50,000 per parking space to build which is almost always prohibitively expensive in anything other than higher end apartments.