In an aspect there is provided a joint assembly 16 for panel board materials, comprising: a first member 14 comprising a tongue 22 extending from a surface 26 of the first member 14, the tongue 22 comprising a first groove 24 in a side 28 of the tongue 22; wherein at least a portion of the side 28 of the tongue 22 including the first groove 24 extends generally perpendicular to the surface 26 of the first member 14; and a second member 12 comprising: a second groove 32 in a surface 36 of the second member 12, the second groove 32 being arranged to receive the tongue 22; and a lip 34 extending into the second groove 32; wherein, in an assembled position, the tongue 22 is arranged to slot into the second groove 32 and the lip 34 is arranged to slot into the first groove 24 thereby to join the first and second members 14, 12.