In a move to further diversify its portfolio, Senior Housing Properties Trust (NYSE: SNH) has agreed to purchase 27 medical office properties for $470 million from CommonWealth REIT. The properties total 2.8 million sq. ft. and are located in 12 states.

Headquartered in Newton, Mass., Senior Housing Properties Trust is a real estate investment trust that owns independent and assisted living communities, nursing homes, rehabilitation hospitals, wellness centers and medical office buildings.

Senior Housing Properties Trust expects to purchase the 27 properties free and clear of any mortgage debts using cash on hand and its unsecured revolving bank credit facility. The company expects the property sales to be completed in a series of separate closings before June 30, 2011.

Senior Housing Properties Trust will have $3.9 billion invested in 326 properties in 37 states, plus Washington, D.C., once the property purchases are completed. As a result of the acquisition, medical office buildings will account for 37% of the company’s portfolio based on rents compared with 25% previously. Independent living and assisted living facilities will now account for 52% of revenues.

The 27 medical office properties to be purchased have a current average occupancy of approximately 95% and are leased primarily to medical services providers and other tenants in medical-related businesses.

The largest of the 27 properties are two office towers totaling 331,000 sq. ft., plus garages for 1,705 cars, which are attached by an enclosed walkway to Cedars Sinai Hospital in Los Angeles. The two office towers are primarily leased to medical practice groups affiliated with the hospital.

Senior Housing Properties Trust was a 100% owned subsidiary of CommonWealth REIT (NYSE: CWH) until it was spun off to CommonWealth shareholders in 1999. Senior Housing Properties Trust has a right of first refusal to purchase certain properties majority leased to tenants in medical-related businesses when CommonWealth chooses to sell assets.

The share price of Senior Housing Properties Trust closed at $22.76 on Friday, Nov. 26, up from $19.97 a year ago.