They've bought a Bacon. Now for a $300,000 settee

Andrew Johnson on the latest craze for members of the world's Big Money club – 'functional sculpture'

It's no longer enough for the world's rich to hang their expensive art on the wall. Now they want to sit on it.

The huge spending power of buyers such as the Russian oligarch and Chelsea football club owner Roman Abramovich, who think nothing of spending tens of millions on a Freud or a Bacon, has driven the rise of a new art discipline. Furniture is too mundane a description for its devotees, who have coined the term "functional sculpture". By whatever name, its sellers are parting the wealthy from hundreds of thousands of pounds for one-off items of furniture created by architects and artists.

Such is the demand for furniture that can hold its own in a room full of the world's most expensive art that the first auction devoted solely to contemporary design will take place at Christie's this autumn.

It will be followed by the Design Art Fair in London, timed to coincide with the Frieze contemporary art fair, which attracts the world's richest and most famous people.

One of the exhibitors at Design Art London will be the Carpenters Workshop Gallery, based in Mayfair. The gallery has just commissioned the artist Marc Quinn, best-known for his sculpture of Alison Lapper, which perched on the fourth plinth in Trafalgar Square in 2005, to create eight marble benches and tables based on his Garden series of works.

The Christie's sale in New York will feature items such as a polyurethane table by the London-based Iranian architect Zaha Hadid, who designed the aquatics centre for the London Olympics, estimated to raise £100,000. Another lot will be a highly polished steel sofa by the British-born Israeli designer Ron Arad for £150,000. Arad's work will be exhibited at the Museum of Modern Art in New York next year.

"It really is an increasingly popular market," said Carina Villinger, design specialist of Christie's New York, which will hold the auction. "There is a huge overlap with contemporary art. It has got to the point where we need a separate auction. Prices have increased dramatically, yet for people who do buy contemporary art, design is relatively small change."

Buyers of what is essentially very expensive furniture include the likes of Brad Pitt and Angelina Jolie. Pitt was spotted at the Carpenters stall at the Design Miami/Basel fair in Switzerland in June, where he reportedly spent around $500,000 (£250,000) on furniture for the family home, including a marble table by the designer Jeroen Verhoeven priced at $293,000 and a rug made of aluminium thread that sells at $175 per square foot. He also thought about buying a gold lacquer-coated fibreglass sofa by Zaha Hadid for $300,000.

Other customers are believed to include Roman Abramovich – who was reported to have spent a record-breaking £60m on Bacon's Triptych and Freud's Benefits Supervisor Sleeping at auction in May.

Contemporary design, says Joanna Needham, the manager of Carpenters Workshop Gallery, inhabits the "grey area between art and design".

"Everything we do is unique or in a limited edition of eight," she adds. "If you are a collector of contemporary art, then you want something on your floor that complements the work on your walls. Many of our customers are contemporary art collectors."

The gallery's owner, Loïc Le Guillard, says: "Contemporary design began in the 1980s, but it has only recently taken off. The wealthy have the same types of cars and homes. Contemporary art and design is one way to stand out. Design art is taking off. We are still just scratching the surface of it. We approach it as a normal art gallery. We are really selling sculpture with functionality. We put on exhibitions and commission artists. Marc Quinn, for example, felt he had something to say."

The design critic Peter York reiterates that buyers who had been going for "wall power" are now looking for "floor power". "The work is fantastic," he says. "It is absolutely like sculpture."