The primary reason they dig those holes is because tall buildings need solid foundations. It's not as if they can just build the building at ground level if onl

The primary reason they dig those holes is because tall buildings need solid foundations. It's not as if they can just build the building at ground level if only it weren't for those darn cars. Foundation depths vary based on too many factors, but a ballpark number for a midsize apartment building is probably in the 15-30% range. So if you have 16 floors, you could reasonably expect to have 2-4 stories below grade. What else would you put there? Even if you only needed 2 stories of foundation depth, digging an additional 2 for parking is relatively cheap compared to the first two, since the equipment is already out there.