In a relatively rare development, a residential deal topped the list of the 25 largest commercial property sales in the first half of the year.

It was the $630 million purchase of Columbus Square, according to data compiled by Real Capital Analytics. The 654-unit Upper West Side development, which includes 710 apartments in five rental buildings, was purchased by a partnership of UDR Inc. and MetLife.

The deal reflects a growing appetite among investors for apartment houses in a city where vacancy rates are low and rents continue to rise.

“Residential properties continue to attract a wide variety of aggressive buyers,” said Douglas Harmon, senior managing director at Eastdil Secured, which represented the sellers on the deal.

It was one of two residential deals in the top five during the first half of the year. The other was Equity Residential’s purchase of 105 W. 29th St. for $280 million, which ranked as the fifth most expensive transaction.

Those two deals came as average Manhattan apartment rents hit their highest level in two years during in the second quarter, according to a report by Prudential Douglas Elliman and Miller Samuel Inc. released earlier this month. The monthly median rent jumped 7.9% to $3,125 in the second quarter from the same period a year ago. It was the fifth consecutive quarterly increase.

Dan Fasulo, a managing director at RCA, added that the strength of the residential market means that potential buyers of the rental buildings can find attractive mortgage rates because the properties are delivering healthy cash flows. That continues to fuel demand.

The largest office deal of this year, which also included a retail component, was Crown Acquisition’s $499 million purchase of a 49.9% stake in 641-649 Fifth Ave., between East 51st and East 52nd streets, also known as Olympic Tower.

That is less than half the value of the largest office deal in the corresponding period last year, when SL Green Realty Corp. and Vornado Realty Trust joined forces to buy 280 Park Ave. for about $1 billion to top the list of the largest transactions. However, that deal, like many others on last year’s list, was born from the previous owners’ debt problems which forced them to sell their properties. That created some major buying opportunities which weren’t as plentiful this year. Owners are reluctant to sell now because they are wondering how they would use the cash when there’s a lack of viable investment opportunities.

Experts say larger deals may return in the second half of this year as some owners move to sell, knowing they’ll likely attract a multitude of potential investors who look at New York City as a safe haven for their money amid global economic turmoil. Eastdil is selling Worldwide Plaza, a mammoth tower on Eight Avenue that is almost fully leased and should fetch in excess of $1 billion.