<P> A structural steel contract was awarded on January 12, 1930, and excavation of the site began ten days later on January 22, before the old hotel had been completely demolished . Two twelve - hour shifts, consisting of 300 men each, worked continuously to dig the 55 - foot (17 m) foundation . Small pier holes were sunk into the ground to house the concrete footings that would support the steelwork . Excavation was nearly complete by early March, and construction on the building itself started on March 17, with the builders placing the first steel columns on the completed footings before the rest of the footings had been finished . Around this time, Lamb held a press conference on the building plans . He described the reflective steel panels parallel to the windows, the large - block Indiana Limestone facade that was slightly more expensive than smaller bricks, and the tower's lines and rise . Four colossal columns, intended for installation in the center of the building site, were delivered; they would support a combined 10,000,000 pounds (4,500,000 kg) when the building was finished . </P> <P> The building's structural steel was pre-ordered and pre-fabricated in anticipation of a revision to the city's building code that would have allowed the Empire State Building's structural steel to carry 18,000 pounds per square inch (124,106 kPa), up from 16,000 pounds per square inch (110,316 kPa), thus reducing the amount of steel needed for the building . Although the 18,000 - psi regulation had been safely enacted in other cities, Mayor Jimmy Walker did not sign the new codes into law until March 26, 1930, just before the steel was about to be laid . The first steel framework was put into place on April 1, 1930 . From there, construction proceeded at a fast pace . During one stretch of 10 working days, the builders erected fourteen floors . This was made possible due to the extremely precise coordination of the building's planning, as well as the mass production of common materials such as windows and spandrels . For instance, after a supplier of dark Hauteville marble could not deliver enough material on time, Starrett switched to using Rose Famosa marble from a German quarry that was purchased specifically to provide the project with sufficient marble . </P> <P> The scale of the project was massive, with trucks carrying "16,000 partition tiles, 5,000 bags of cement, 450 cubic yards (340 m) of sand and 300 bags of lime" arriving at the construction site every day . There were also cafes and concession stands on five of the incomplete floors so workers did not have to descend to the ground level to eat lunch . Temporary water taps were also built so that workers did not waste time buying water bottles from the ground level . Additionally, small railway systems carried materials from the basement storage spaces to elevators that brought the carts to the desired floors, where the carts then delivered the materials across that level directly by using another set of tracks on that floor . The 57,480 short tons (51,320 long tons) of steel ordered for the project was the largest - ever single order of steel at the time, comprising more steel than was ordered for the Chrysler Building and 40 Wall Street combined . According to the historian John Tauranac, the materials for the building came from far and wide, with "limestone from Indiana, steel girders from Pittsburgh, cement and mortar from upper New York State, marble from Italy, France, and England, wood from northern and Pacific Coast forests, (and) hardware from New England ." Even the facade used a variety of material, most prominently Indiana limestone but also Swedish black granite, terracotta, and brick . </P> <P> By June 20, the skyscraper's supporting steel structure had risen to the 26th floor, and by July 27, half of the steel structure had been completed . Starrett Bros. and Eken endeavored to build one floor a day in order to speed up construction, a goal that they almost reached with their pace of ​ 4 ⁄ stories per week; prior to this, the fastest pace of construction for a building of similar height had been ​ 3 ⁄ stories per week . In the meantime, the final designs for the floors were being designed from the ground up (as opposed to the general design, which had been from the roof down). Some of the levels were still undergoing final approval, with several orders placed within an hour of a plan being finalized . On September 10, as steelwork was nearing completion, Smith laid the building's cornerstone during a ceremony attended by thousands . The stone contained a box with contemporary artifacts such as the previous day's New York Times; a U.S. currency set containing all denominations of notes and coins minted in 1930; a history of the site and building; and photographs of the people involved in construction . The steel structure was topped out at 1,048 feet (319 m) on September 19, twelve days ahead of schedule and 23 weeks after the start of construction . Workers raised a flag atop the 86th floor to signify this milestone . </P>

Where did the steel for the empire state building come from