At the peak of construction, 3,500 workers were employed on the Empire State. The 57,000-tonne (62,831-ton) steel structure was encased with 10 million bricks and 1,553,000 cubic feet (44,000 cubic metres) of concrete. Easy access to the roof was possible after 67 separate elevators were installed. Over the next few weeks, glazers put in 6,400 windows and plumbers laid 51 miles of pipe to service 2,500 toilets. Most amazingly, it was all done in just 11 months.