Quote:
Originally Posted by HomrQT
It's interesting that laying an extra foundation, adding a new set of mechanical and utilities floors, dedicating more space to a separate entrance floor, putting a separate roof, and building a second tower that will partially obstruct views and take up land space that could be used for tenant activities and leisure is cheaper than adding more floors going up.
|
You have to consider that for each floor you pour, you have to fill the "slick line" full of concrete to the elevation of the floor. This is the line from the concrete pump that pushes the concrete up to the pour. Say the line is 8" diameter and 1400' high. The volume of that line is about 1 concrete truck. When you finish the concrete pour, you have to pump that line full of grout to clear it out and you pour all that grout into a disposal container and throw it away.
At high heights, every piece of material you have to pull up the building with the crane takes that much longer - durations stretch, etc.
At higher heights, the occupancy count of the building increases - this adds elevators which reduces floor area.
Foundation costs for one taller building are only slightly less than for two smaller buildings. You have twice the load coming down and so much more lateral to account for.
Mechanical cost comes from floor area, not count of plants. You still have the same area to heat and cool. With a single taller building, your shafts will grow larger as you approach your makeup air unit / exhaust fans, etc. You lose a lot of floor area because of this as Zerton mentioned.
With equal areas, the cost to build the 90th floor is not equal to the cost to build the 2nd floor.
Some neighborhood groups would tell you they'd rather have two shorter towers than one tall one - those people are a complete crapshoot!