PORTLAND (AP) — Portland’s Planning Board has approved a $40 million expansion at Maine Medical Center that would add four operating rooms.

The board unanimously approved the project on Tuesday.

The 40,000-square-foot addition will be built on top of the Lower Bean Building, near the emergency room.

The project will also allow the hospital to expand its existing operating rooms from an average of 400 square feet to 650 square feet.

Hospital officials told The Portland Press Herald (http://bit.ly/12qrhJG ) that larger operating rooms will allow more space for advanced procedures — some of which require surgical teams of 15 to 18 people.

Construction could start this winter and be finished by spring 2015