Box formed building panel of extruded plastic

A box formed building panel formed of, preferably transparent, extruded plastic materials, said panel having opposing side walls and end walls normal thereto, said panel containing partition walls forming a plurality of internal hollow spaces;

• one of said end walls having a groove (114) extending along its entire length and running parallel to said side walls, the bottom of said groove being defined by a partition wall (113) adapted to support a resiliently deformable sealing material (149), the walls (115, 116) of said groove and their junction with said bottom partition wall being inwardly spaced from the side walls of the panel, said groove walls being outwardly diverging and including converging locking shoulders (131, 132);
• the other of said end walls having a projection (135), the cross-sectional configuration of which is generally complementary to the cross-sectional configuration of said groove (114), said projection having locking shoulders in the walls thereof lockingly engageable with the locking shoulders of the groove walls of an adjacent, similarly formed building panel for joining the panels together, said end walls having wall portions in the areas not occupied by said groove or projection abuttable when the projection of one panel is inserted in the groove of an adjacent panel.