A shutter panel assembly for attachment to existing building shutters and comprising a front shutter panel member decorated or capable of being decorated and which is formed to include rearwardly disposed wall flanges having inturned edges to which a second shutter panel member may be attached for providing a back wall and an enclosed space for electrical wiring and other uses therebetween. And slot openings in the side wall flanges of the front panel member near its top and bottom edges through which are projected adjustable clamp arm assemblies under the tension of a biasing spring between the panels for self-adjustment thereof and retentive engagement with the side edges of a supportive regular shutter therebehind.