A shutter assembly having a shutter with louvres, and a border frame for surrounding the shutter which is attachable to a building and having a plurality of frame side sections each formed of sections of extruded plastic, a plurality of hollow tubes, separated by thin walls, defined in the sections, a fastener channel formed integrally in the frame side sections for receiving fasteners for holding the shutter assembly in place, and, an extruded plastic removable cover plug channel having flexible side walls for fitting in the fastener channel and closing the channel and thereby concealing heads of the fasteners.