Public and semipublic institutional buildings may be erected to a height not exceeding 60 feet, provided the yard shall be not less than the height of the building wall abutting on the yard, except that flagpoles, antennas, towers, and mechanical appurtenances located upon and designed in connection with the building may be erected above the height limit, but not to exceed 100 feet from the finished grade. (1980 Code 151.05)