DETROIT -

Rock Ventures announced Tuesday the purchase of five downtown Detroit buildings, bringing the company's total to 15 buildings in the heart of the city.

The company, founded by Quicken Loans chairman Dan Gilbert, now owns 2.6 million square feet of commercial space and three parking structures in downtown Detroit. Rock Ventures has acquired eight downtown Detroit buildings in 2012 alone.

Related: Dan Gilbert's latest Detroit purchase, One Woodward, may be his crown jewel

The buildings most recently purchased by Gilbert's company include 1201 Woodward Kresge Building, 1217 Woodward, 1412 Woodward, 1301 Broadway Cary Building Lofts and 1521 Broadway Small Plates Building. The buildings will be renovated for retail and office or residential use.

"It has been an exciting year of opportunity in Detroit,” said Gilbert in a news release. "Our focus in 2013 will be on the three R’s – residential, rail and retail – all of which are vital in creating the vibrant, thriving urban core that we all envision."

Matt Cullen, of Rock Ventures, said the final tenants are not yet known.

"We don't have the final tenants identified for the five buildings, but of the buildings we have bought so far they are almost already all full. So, we think we can continue to do that," Cullen said. "Not only do we, Rock Ventures, have momentum but the city of Detroit has momentum."

The purchases were brokered by Rock Ventures' very own real estate firm Bedrock Real Estate Services.

Earlier this month, Gilbert and his partners at Rock Ventures purchased One Woodward, an iconic Detroit building which once housed Michigan Consolidated Gas. It was designed by the same firm which designed New York's World Trade Center towers.