The height limitations of this chapter do not apply to any roof-mounted flagpole, mast, monument, standpipe, amateur radio tower, belfry, elevator bulkhead, chimney flue, church spire, clock tower, scenery loft, stage tower, television antenna, water tank or similar appurtenances usually carried above roof level; provided, however, that in no event shall such appurtenance exceed sixty (60) feet in height from curb level, and in no event shall the aggregate horizontal base area of such appurtenance(s) exceed twenty-five percent (25%) of the roof area.