Why not make storage spaces?

Because that would convert space really badly. If you're making 10'x10' rooms out of a 100'x100' space, it's 74% dead space. If a floor is more than 10,000 sq feet, maybe 40,000 sq feet, it goes up to to 90%.

I mean, numbers are made up, but the point holds.

I’d be interested to see people get really creative with it. Throw a gym in on one floor. Cinema room on another. Storage units in a few more. Probably difficult to structurally support a pool on a floor not already designed for one but sure, let’s throw one in there too. A kids playroom is maybe a little depressing with no natural light but it could work. Hell: keep the middle commercial space and put a grocery store in.

Obviously once you’re talking about true high rises you’re going to run out of possibilities and I know the maths is still very rough. But it’s an interesting thought exercise to think about just how many amenities you could pack into a building.

Sound like what inevitably happens to my Sims games, just start filling in those gaps

Dance floor #3? Make it happen!

Funnily this is kind of possible. Tokyo has at least one dance club located in a residential high-rise, just padded enough that the sound doesn't carry into the apartments around it. It's been a while though and I can't find the name now - please post a link if anyone remembers where it was.

Liquid room?

20 Exchange in NYC is like that. Each chunk of floors gets a nearby amenities pod, with singletons for the really expensive stuff. Still, I think you’d have to get a screaming deal on the building in order to be able to make that economical.

Another use for interior rooms could be meeting/ conference rooms/ teleconference/ coworking spaces. Some premium apartment landlords currently have these in their clubhouses, usually reservable by the hour, residents usually get so many free credits a month.

Is this a thing, in planned conversions? If the pricing varied by day and time, or was dynamic, it could work very well. With secure lockers adjacent. (Would that require mixed-use zoning?)

A teleconference room (/remote classroom) by day could be time-multiplexed into a cinema room off-peak (with some compromise in seating plans), leasing company just needs to handle cleaning deposits and video surveillance at start and end to check users keep it clean.

I know your numbers are made up but presumably an apartment is much deeper than 10'. You'd want to make it as narrow and deep as practical. 20x45'? 25x36'?

I get that you get (almost) twice as many apartments (presuming you don't build up higher), but you also get a massive and complicated one time cost. It surprises me that it could ever be worth it.

I call this the Chicago layout -many apartments are long and narrow. I have assumed it was to ensure access to two fire escapes. Too hazard a guess, I have seen some that might only be 15’ wide, supporting a 10x10 room with a hallway to access it.

Chicago lots are long and narrow. Typical Chicago residential lot is 25x100 or so. Street in front, alley in the back, garage if you have one is a separate building fronting the alley. Many houses are built as "two flats" or "three flats" i.e. two or three houses stacked on top of each other.

I was a bit surprised by this, but, yea, pulled up random part of chicago and it's basically exasctly as described.

https://www.google.com/maps/place/Chicago,+IL/@41.7332309,-8...

This is really common in and around Boston too. The architectural style is from the area and we cal them three deckers (in Boston) or triple deckers (everywhere else). Lot size is probably similar, and they’re still highly valued (if kept up) to this day because of their construction and other benefits. I live in one now and others around me go for 750k+

https://www.dotnews.com/columns/2014/glorious-three-decker

You could make the rooms bigger. Also surely they aren’t always squares which is the worst case.