Abstract: A panel of molded plastic or cured composite materials configured to span the space between a pair of beam or support members by a slideable engagement between each of the opposite ends of the panel and its adjacent beam or support member, and the panel sealingly and lockingly engageable along each of its opposite edges to another panel adjacent each edge of the first panel. The panels are fabricated whereby the panel end engagement means with the beam or support members define a predetermined path which in turn is variable as the panels can be arcuately flexed widthwise upon installation engagement with the beam or support members while at the same time minimizing load deflection of the panels lengthwise when installed.