Abstract: A modular structural element, including a planar surface layer of cladding material. A substrate layer is bonded to the surface layer and includes an outwardly-extending attachment flange defined by the thickness of the substrate layer and proximal to the surface layer around two adjacent side edges for receiving fastener elements through the thickness of the substrate layer and into the support member. A tongue projects outwardly from the flange remote from the surface layer. Two spaced-apart elements define a groove therebetween extending along adjacent sides of the substrate layer for receiving the tongue of a complementary adjacent structural element. The flange resides at all points intermediate the tongue and the surface layer for permitting the tongue to float within the groove of the complementary structural element for preventing damage to the surface layer resulting from relative movement between adjacent structural elements.