Burj Khalifa would be tall. This was reported in a Council on Tall Buildings and Urban Habitat study, which notes that the empty spire "could be a skyscraper on its own". Such a skyscraper, if located in Europe, would be the 11th tallest building on that continent. In 2009 architects announced that more than 1,000 pieces of art would adorn the interiors of Burj Khalifa, while the residential lobby of Burj Khalifa would display the work of Jaume Plensa. The cladding system consists of of more than 26,000 reflective glass panels and aluminium and textured stainless steel spandrel panels with vertical tubular fins. The architectural glass provides solar and thermal performance as well as an anti-glare shield for the intense desert sun, extreme desert temperatures and strong winds. The glass covers more than in area. The Burj's typical curtain wall panels measure wide by high and weigh about each, with wider panels near the building's edges and taller ones near the top. The exterior temperature at the top of the building is thought to be 6 °C (11 °F) cooler than at its base. A 304-room Armani Hotel, the first of four by Armani, occupies 15 of the lower 39 floors. The hotel was supposed to open on 18 March 2010, but after several delays, it finally opened to the public on 27 April 2010. The corporate suites and offices were also supposed to open from March onwards, yet the hotel and observation deck remained the only parts of the building which were open in April 2010. The sky lobbies on the 43rd and 76th floors house swimming pools. Floors 20 through 108 have 900 private residential apartments (which, according to the developer, sold out within eight hours of being on the market). An outdoor zero-entry swimming pool is located on the 76th floor of the tower. Corporate offices and suites fill most of the remaining floors, except for the 122nd, 123rd, and 124th, where the At.mosphere restaurant, sky lobby, and an indoor and outdoor observation deck are located respectively. In January 2010, it was planned that Burj Khalifa would receive its first residents in February 2010. The building has 57 elevators and 8 escalators. The elevators have a capacity of 12 to 14 people per cabin, the fastest rising and descending at up to for double-deck elevators. However, the world's fastest single-deck elevator still belongs to Taipei 101 at