One of the biggest factors that drives construction costs:
Site access.
If you've got tight streets, overhead powerlines, limited parking, no room for a dumpster or laydown, enthusiastic meter maids, etc...
It'll cost ya.
We've done projects in the tightest of all locations: the highrise downtown apartment building. No freight elevator, no storage...everything had to be hand carried in and out, the subs had to find parking garages that accommodated their trucks, there had to be offsite storage for fixture, material, and finish deliveries.
And...the building was fully occupied by lots of folks who don't want their daily routines disrupted.
It probably doubled the cost of the project.

Think about it this way: the plumber has to park in a garage that's a 15 minute walk from the building. It's an expensive downtown garage [so the client pays for that], and he's got to carry all his stuff in and out. If he makes multiple trips, or forgets something in his truck...there goes another 30-45 minutes.
That means that every 8 hour day, you might only be getting 5-6 hours of real work.
Multiply that times all the subs and all their crews.
Plus, the guys have to protect their work, hand carry everything in the fancy elevator [many buildings have freight elevators, so that helps], and make sure not a single dusty bootprint is left on the common hall carpets.
There aren't many subs who want to work with that level of hassle, so the ones who are willing can charge a premium.
That's an extreme example, but I see it with my other clients as well, both residential and MF. When I go meet someone about renovating their house, and I see a tough site...I have to tell them it's going to cost $$ to deal with that. On MF projects, these problems can be amplified, because the project itself is bigger and there are more crews and materials.
When you google "construction prices," stuff like this doesn't come up, because it's so site dependent. Even GC dependent - if you hire the cheap guy who's not used to the issues on a tight site, you're going to get into serious trouble real fast.
This is why you need experience and a solid team around you...this stuff will wallop you otherwise.
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