have entailed the construction of several smaller office buildings. The UN could not secure funding for the project at the time. Following the September 11 attacks in 2001, the Secretariat Building's curtain walls were covered with a green coating, which was intended to limit damage in case of a bombing. In 2002, Secretary-General Kofi Annan proposed replacing the Robert Moses Playground with a new tower, relocating the Secretariat's offices there temporarily, and renovating the Secretariat Building itself. The UN selected Fumihiko Maki to design a building on the Moses site, but the New York State Legislature refused to pass legislation in 2005 that would have allowed these plans to proceed. The UN then decided to renovate its existing structures over a seven-year period for US$1.6 billion. The Secretariat Building would be renovated in four phases, each covering ten stories, and the UN would lease an equivalent amount of office space nearby. Louis Frederick Reuter IV originally designed the renovation, but he resigned in 2006 following various disputes between UN and US officials. Michael Adlerstein was hired as the new project architect. Engineering firm Skanska was hired to renovate the Secretariat, Conference, and General Assembly buildings in July 2007. At that point, the cost of the project had risen to US$1.9 billion. Prior to the start of the renovation, in 2008, Secretary-General Ban Ki-moon approved a pilot program to reduce heat emissions by raising temperatures throughout the building. By then, the offices had been rearranged so frequently that the heating and cooling system no longer worked as intended. Substantial renovation and reopening The renovation of the United Nations headquarters formally began in 2008. Adlerstein planned to reconstruct the Secretariat Building's offices entirely while preserving the appearance of the exterior and public spaces. All of the building's 5,000 workers had to relocate to nearby office space. Work on the building began in mid-2010. The work involved redesigning the mechanical systems, adding blast protection, and upgrading the building to conform to New York City building codes. In addition, large amounts of asbestos were removed from the structure, and workers installed a fire-alarm and sprinkler system. The curtain wall was also rebuilt in several sections, starting from the lowest levels and working upward. The building was also retrofitted with various green building features as part of the project. The building reopened in phases, with the first workers returning in July 2012. On October 29,