Chicago's Willis Tower on the market

The tallest building in North America, Chicago's Willis Tower, formerly the Sears Tower, is on the block, with its owners searching for a buyer or investor.

The 108-storey building is 18% vacant, and a source told The Wall Street Journal  that owners would be willing to consider either a sale or recapitalisation.

The 442-metre building is owned by a consortium including New York-based investors Joseph Moinian and Joseph Chetrit and American Landmark Properties, which bought the property for US$841 million in 2004.  It is one of the most popular tourist attractions in Chicago, drawing an average of 1.5 million people a year to its Skydeck.

The tower, with a total enclosed area of approximately 424,000 gross square metres, has a rentable area of 353,000 square metres. Its antennas soar to 527 metres.

Designed by architects Skidmore Owings and Merrill, the 1973 tower was originally the headquarters of Sears Roebuck and Co, which moved to Illinois in the early 1990s. 

Within the building, there are 45 kilometres of plumbing, 2,414 kilometres of electric wiring, 130 kilometres of elevator cable, and 145,000 light fixtures. The building cost more than US$175 million to build.

In 2009, the owners negotiated a naming rights deal with London-based Willis Group Holdings, which moved 500 employees into 13,000 square metres at US$156 per square metre.

It could be difficult to find a buyer for the landmark building, however, as the GFC hit the United States hard and the economy is struggling to recover. Last week's residential housing figures revealed that residential prices in the United States have fallen further than they did during the Great Depression.

It will not remain the tallest building in North America for long, however, as the partially completed Freedom Tower at One World Trade in New York will be 105 storeys and 541 metres tall. Freedom Tower, which recently signed its first major tenant, magazine empire Conde Nast, is expected to be completed by early 2014.