The investment arm of Kuwait’s social-security system bought a luxury apartment building in Manhattan’s Noho neighborhood, as demand for multifamily properties surges, two people with knowledge of the deal said.

Wafra Investment Advisory Group Inc. last week completed the purchase of 2 Cooper Square, a 144-unit building that includes a rooftop pool, video-game center and private movie- screening room, said the people, who didn’t disclose the price and asked not to be named because the deal hasn’t been made public. The owner was Atlantic Development Group LLC, a Manhattan-based builder that finished the tower in 2010, according to the property website.

“The rental market is so competitive in New York and newer buildings are going to be the most competitive,” Ben Thypin, director of market analysis for Real Capital Analytics Inc., said in an interview.

The dollar volume of Manhattan apartment-building sales more than doubled in 2011 from the previous year to $4.58 billion, according to data from New York-based Real Capital. About 195 properties changed hands, up 43 percent from 2010. Manhattan apartment investors paid an average of $456,796 per unit last year, up 57 percent from 2010. Nationally, multifamily investors paid about $101,925 per unit, the research firm said.

Other Manhattan Deals

Edward Ryan, a Wafra representative in New York, declined to comment on the Cooper Square deal. Julie Halpin, a spokeswoman for Atlantic Development, didn’t respond to an e- mail and telephone message seeking comment today. The broker on the deal, Doug Harmon, senior managing director at Eastdil Secured LLC, didn’t return a phone call today. Neither did Martha Wallau, a spokeswoman for Eastdil.

The deal is the second in the past two weeks for a new rental apartment property in Manhattan. On Jan. 12, UDR Inc., the third-largest publicly traded U.S. apartment owner, and MetLife Inc. said they bought a five-tower apartment complex on Manhattan’s Upper West Side for about $630 million. It was the fifth apartment purchase in the borough for Highlands Ranch, Colorado-based UDR.

Investors have been willing to pay more for Manhattan’s newly constructed apartment buildings because they have lower operating expenses and tend to attract wealthier tenants, Thypin said.

‘Paying a Premium’

UDR and MetLife paid $887,000 per unit in the Columbus Square complex, according to Thypin’s analysis. TIAA-CREF’s purchase in May of the Corner, a 196-unit building on the Upper West Side, valued the apartments at $1 million each, he said.

“Buyers are comfortable paying a premium right now with the hopes that rents are going to increase in the next few years, which I think is very realistic,” Thypin said.

The median effective rent for Manhattan apartments, or what tenants paid after landlord-sponsored incentives, rose 9.5 percent in the fourth quarter from a year earlier to $3,121 a month, appraiser Miller Samuel Inc. and broker Prudential Douglas Elliman Real Estate said in a Jan. 12 report.

At 2 Cooper Square, available one-bedroom apartments rent for as much as $6,686 a month, according to the property’s website. A two-bedroom unit is listed for $9,335 a month, while a four-bedroom apartment commands $22,000 a month.