A Charleston company that’s grown into one of the nation’s largest players in the apartment business is expanding its portfolio in a big way.

Greystar Real Estate Partners said Monday it has struck a deal to buy 27 properties with more than 8,000 rental units for $1.5 billion under a joint venture with New York’s Goldman Sachs & Co.

The seller is Chicago-based Equity Residential, the nation’s largest publicly traded apartment owner. It plans to use the sales proceeds to help finance its purchase of rival landlord Archstone Inc.

Greystar is getting properties spread across seven major U.S. cities and regions, including Washington, D.C., Denver and San Francisco.

“For us, it was an opportunity to handpick a portfolio of assets in all of our favorite markets around the country with a very motivated seller,” said Bob Faith, Greystar’s founder, chairman and chief executive officer.

The sale is expected to close in March. It will boost the number of units that Greystar either owns outright or manages for other investors by about 4 percent to 208,000.

“We remain very bullish on the apartment industry, overall,” Faith said Monday.

All of the Equity Residential properties are in markets where Greystar already has property management offices.

“This transaction fits perfectly in our investment strategy to acquire assets with strong existing cash flows at values below replacement cost located in markets with high employment and population growth,” said Faith, who was former Gov. Mark Sanford’s first commerce secretary from 2003-06.

Greystar also is investing $1.5 billion in new developments around the country, including Elan Midtown near Meeting and Spring streets in downtown Charleston.

The 200-unit property is the first new major apartment deal for the peninsula in more than 25 years. It’s expected to be ready for occupancy by middle of the year.

“It’s on schedule,” Faith said.

Contact John McDermott at 937-5572.