[rplst8]

> Look at all the 3 or 4 stories apartment buildings sprouting in the city right now. Most of them could be double the height without increasing construction costs per unit.

I'm not sure that's correct. I think the reason that you see a lot at that height is because building codes change quite a bit as you go past a certain height and the costs go up as well.

[surrealize]

The height limit you're thinking of is higher. The IBC allows for five stories of wood construction over a multi-story concrete podium (often one or two stories).

http://www.structuremag.org/?p=10934

The main height limit is local politics around density, not building codes.

[coredog64]

IIRC, 3 stories is about the max that US building codes allow for stick built structures. Beyond that you have to go to steel.

3-4 is also where you need to start thinking about adding an elevator. That adds to the cost and reduces the area available for units.

[ThrustVectoring]

AFAK this is what the codes are. When I see building frames under construction, I see an awful lot of "three floors of wood framing above a steel base" (usually mixed-use commercial 1st floor with residential above, but I'm assuming things here)