Inova Health System trustees have approved a $23 million addition to Inova Mount Vernon Hospital, the third phase of a multi-year campus modernization program that’s caused strife with the surrounding community at times.

The 21,000-square-foot addition, with construction slated to begin in 2014, will eventually house the hospital’s emergency department, which will be relocated from its current location.

The old space will be reused for new service lines, spokeswoman Rita Wakefield said.