One World Trade Center has reached a construction milestone by rising 260 ft above street level. Upon its completion in 2013, it will become the tallest office building in the United States reaching 104 stories. Currently standing at the 26th floor level, the 1,776-ft-tall office building is being designed by David Childs of Skidmore, Owings and Merrill (NY office) and developed by the Port Authority of New York and New Jersey and is scheduled to reach a height of 50 stories by the end of 2010. To date, more than 67,000 cubic yards of concrete have been poured for the tower, both above and below ground exceeding the amount of concrete used to build the entire Empire State Building. One World Trade Center will incorporate design elements based on LEED Gold criteria with energy efficiency running 20% higher than city codes presently require. Seen at GreenSource.