There was a time when many of us on this board lived in buildings without personal bathrooms and only shared facilities. Dorm style housing could work.

For who?

For the Millennials with proper jobs that never could buy a house, still live at their parents, and are inclined to communal ideas that lower the impact of individuals on their environments.

Once you are 30+ and have a family it becomes much less acceptable

Is it easier than earning nothing because nobody is going to use the building otherwise?

That's the wrong question.

The right question is "Is it easier than tearing down the building and building a new one that's designed for residential use in the first place?".

It's not easy but it's also just like an ordinary phase of construction. They have to strip it down and replumb it, which in construction also just looks like drilling big holes through the floor.

What they're saying is the buildout from commercial to apartments involves more work than the buildout from one commercial client to another.

Drilling big holes, cutting the slab etc.

Also if it is a tension slab you absolutely cannot cut into it.

Luxury conversions - 2 apts max per floor? — could address the single shared utility risers/core of the typical office building. Schematically: [ a | util | b ].

Malls are also on the table for conversions these days. That is a much simpler transformation.

Why are malls simpler to transform? All the malls I'm familiar with have relatively few bathrooms per floor, and huge interiors (low wall:floor ratio) that would seem hard to slice up into apartments.

It is far easier to add plumbing to the ground floor of a building. In fact everything is easier if you’re not 1000 feet in the air.

Was discussing the same with dad when walking through a nearly abandoned mall in MD a while ago. Think a sort of gated community - anchor stores can become things like WholeFoods. Reclaiming a ribbon of parking around the mall allows for creating a green zone around the mall and possibly even ‘backyard’ gardens. And as noted by others, it is far more trivial to add the necessary infrastructure to support housing. Natural light is another issue which can be addressed with minor alteration to the external facing walls of stores. Basically you can easily stamp out big studios, merge stores for n-bedrooms, and depending on the structure of the mall possibly even punch through floors for duplexes, etc. These will be luxury units. And the ‘food court’ etc. can form the core of the ‘village’.

Don't offices have much more floor height than apartments? So just add stuff in the ceiling or raise the floor and run stuff under there.

Plumbing and windows are too hard. So, let’s not do it.