[usrusr]

But do you really have to cram in as many residents as you could with a purpose-built tenement? There must be ways to keep headcount in the range the infrastructure can support and still provide a lot more housing than just leaving them as empty decaying offices owned by the last one holding the bag. Intersperse flats with windowless storage units (you have a depth problem anyways), low density commercial use like workshops with live-by flats and so on. Large units designed to attract high squarefeet/low headcount tenants, not bunk bed families. Add regulation only as a fallback limiter. Don't let perfect be the enemy of good.

[pseudalopex]

> There must be ways to keep headcount in the range the infrastructure can support and still provide a lot more housing than just leaving them as empty decaying offices owned by the last one holding the bag.

Demolishing the office building and building a residential building is more profitable often.

[vel0city]

I mean, sure, you can just sell it as a unit for each floor. You then need to recoup all the costs of rebuilding against fewer people, so all the main area renovations and what not get more expensive and the monthly cost of building maintenance get spread across fewer and fewer tenants. But you've still got a problem of most of the rooms of your very expensive condo have zero natural light, its all practically ancient built stuff in terms of planned structure life, and you've got a very expensive monthly maintenance bill. Meanwhile your massive and dark unit with odd plumbing and low ceilings is competing in the market against units that were actually built for the purpose of people living in them, so while your unit is big and expensive to maintain they're some of the least desirable spots.

The economics just often work out a lot better to tear down the old structure and rebuild a new one more fit for purpose.

[vel0city]

Sorry, I either totally misread your comment or was mentally replying to someone else when I wrote this.

Sure, you could just cram the residences to the edges and try to recoup the cost of the rest of the square footage for places that don't need natural light. But once again you've got issues with original designs and intents for the building. None of the plumbing is designed to be pushed to the edges, so you'll need to make massive changes to the structural integrity by drilling a bunch of new floor cores to do all the new plumbing work. You could rent the interior spaces as storage, but you'll probably quickly flood the market of storage units with the massive amount of square footage you'll be bringing.

Trying to have industrial in there as well is asking for problems. Trying to rent some 15th story small/medium interior unit as some kind of industrial workshop would be quite weird. What kind of industry would want a smaller interior space that probably can't support heavy equipment, has a limit to ceilings of ~10 or so feet, can't require odd ventilation or strange/additional fire suppression/separation requirements, probably has significant power limitations (in terms of industrial capacity, at least), noise limitations, difficulty getting much product in and out, etc? Stuff that the city is going to be OK zoning literally across the hall from people trying to live? And that you're going to find a number of these willing to pay a good bit for such a space to cover the maintenance costs? These buildings weren't built for industrial usages, they were built for office desks and couches. Maybe a few floors have been upgraded to handle additional weight to have datacenter kind of spaces, but definitely not most of the floors.

So then you're trying to spread the maintenance costs of this massive and old building across higher value residences and a lot of very low value storage/weird industrial tenants.

[mothballed]

You can run drains out the side of the structure without drilling holes in the floor, same with electric, and even if by some insanity we say "whutabout the holes in the side" then you could even use a damn lift pump/macerator pump to pump it up and out through where a window was. For vents you can also use AAV instead of a traditional vent. If the residences are at the edges they should be able to pop right out and worse case you elevate the floor in the bathroom/kitchen under the plumbing appliances for the slope on the pipe as it exits. A vertical drain pipe isn't going to freeze (and even if it were, could be insulated and heated), and supply lines are such small holes as to not threaten structural integrity.