With class A rents pushing up into the triple digits for the best buildings, some owners are happy to stick with their class B properties.

“The stock of B buildings is not increasing, it is decreasing,” said Berndt Perl, a partner in APF Properties, which owns several midtown class B buildings and is buying more.

Perl says they are also seeing good traffic to their properties. “Our portfolio had a lot of vacancies last year and then [suddenly] we could have filled everything, and we pushed rents. Now we are a little more selective,” Perl said. “Activity is clearly in those smaller firms, and for them the class A towers are not an alternative.”

Along with Prudential Real Estate, APF is in contract to buy 28 W. 44th St. for $161 million from the former king of Bs, SL Green Realty Trust, which since becoming a publicly traded company, has refocused on class A stock.

“I love the block,” said Perl of W. 44th Street between Fifth and Sixth Avenues, which is filled with tony clubs. APF’s headquarters is in their property at 25 W. 45th St., which can be accessed by walking through another mid-block building, 19 W. 44th St., that SL Green sold at the end of last year for $123.15 million to Deka Immobilien Investment.

“We see a lot of upside and a lot of potential,” said Perl about 28 W. 44th. “We have a lot of angles to work the building and are planning a fairly extensive capital improvement campaign.”

Depending on when leases were signed, most are in the low $40s a foot with new ones coming in from the high $40s to low $50s a foot.

APF also owns 1156 Ave. of the Americas, 286 Madison Ave. and 290 Madison Ave., as well as 24 W. 57th St. The company sold 636 Ave. of the Americas to Billy Macklowe and ING Clarion earlier this year for $45.23 million as they started to laser-focus on the Grand Central district.

“When you are in the niche of providing space for service firms, there is not going to be more B space, but there is becoming less,” said Perl. The B buildings are being converted to residential and hotels, and occasionally some buildings are demolished. “They don’t build prewar buildings anymore,” said Perl.

There is always demand for class B buildings, agreed Carri Lyon, a broker with Cushman & Wakefield. “In Midtown South and Chelsea many of the buildings we used to rent years ago were made into residential lofts.”