ECONOMIC HEIGHT The economic height of a skyscraper refers to the number of stories that will produce the highest rate of return on the money invested. At some point in the construction of every highrise, the law of diminishing returns sets in, and rents for the additional stories do not cover costs. Taller buildings require more substantial foundations, wind bracing, and mechanical systems--but by far the greatest price of extra height lies in the requirements of efficient vertical transporation. Elevators are expensive to build and to operate, but their major cost accrues in the large volume of non-rentable space consumed by the shafts.
	Among the variables affecting the equation of economic height are the size of the building's lot, which influences the efficient layout of the floor plan; the price paid for the land; the cost of construction and financing; and the anticipated rates for rents. Developers, architects, and general contractors prepared charts that compared construction costs for buildings of various heights erected on the same lot. In the late 1920s, for example, the per�square�foot cost for structural steel for a 30-story building was around $.95, while for a 65-story building, it was $1.35. The higher number came from the extra steel required to carry the weight of additional stories and the need for wind bracing. The benefit was added floors of rentable space that would produce revenue for years to come.
	In the 1930 book, The Skyscraper: A Study in the Economic Height of Modern Office Buildings, a team of professionals compared the costs for buildings of eight different heights on a 200 x 405-foot lot and determined that, for land valued at $200 a square foot, the economic height was 63 stories. After 1961 when the new zoning law established the floor-area ratio (FAR), setting a limit on volume for a given site, these formulas were moot.

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