The ultra-luxury housing market is scaling new heights as a record number of properties around the world command prices topping $100 million.

Demand for mega-mansions and penthouses has accelerated as wealthy buyers seek havens for their cash and search for alternative investments such as art and collectible real estate, according to a report Thursday by Christie’s International Real Estate, owned by auction house Christie’s. Five homes sold for more than $100 million last year, with at least 20 more on the market with nine-figure asking prices, the brokerage said.

“You’re looking at a universe of over 1,800 billionaires who are starting to become members of this club of collectors of the most unique and incredible real estate in the world,” Dan Conn, chief executive officer of Christie’s International Real Estate, said in a telephone interview. “It’s something they’ll hold onto for a lifetime, the same way they’ll hold onto a Picasso or a Warhol or any number of the great pieces of art we’ve sold over the years.”

Sales are likely to increase this year with more newly built properties and off-market homes trading for at least $100 million, Conn said. Demand is growing among affluent Americans and Europeans; billionaires from unstable economies, such as Russia and Middle Eastern countries; and buyers from mainland China, who were barred from investing overseas before 2012 and since have snapped up houses in cities including Hong Kong, Los Angeles, New York and London, he said.

‘Can Boast’

“People want trophy homes,” Eyal Ofer, a Monaco-based shipping and real estate magnate, said in interview earlier this week at the Milken Institute Global Conference in Beverly Hills, California. “They’re a scarce commodity. And they’re better than gold because you can boast about it.”

Last year’s sales of homes for at least $100 million were led by an East Hampton, New York, estate purchased for $147 million for by Barry Rosenstein, managing partner at hedge fund Jana Partners. The other top sales were a $146 million villa in Saint-Jean-Cap-Ferrat, France; a $120 million estate in Greenwich, Connecticut; a $104 million Hong Kong residence; and a $100.5 million duplex penthouse in New York’s One57 condominium tower, according to Christie’s.

Not all the properties went for close to the asking price. The Greenwich estate that sold for $120 million was originally listed for $190 million.

“You’re really pricing the unpriceable,” Conn said.

Just one home sale exceeded the $100 million mark in 2013, following four such transactions in 2012 and three in 2011, Christie’s reported.