Thirteen sites across Kentucky are being considered for inclusion on the National Register of Historic Places.The sites must first be approved by the Kentucky Historic Preservation Review Board, which meets this week in Harrodsburg.The board then forwards approved nominations to the National Park Service, which will make the final determination.The sites under consideration this time include structures in Bardstown, Murray and Covington and several downtown historic districts.Inclusion on the National Register can make a property eligible for tax credits for rehabilitation projects, and protection from certain encroachment.Kentucky ranks fourth in the nation in the number of sites listed on the register.