Abstract: A wall block (10) comprises a substantially rectangular core (11) of substantially rigid insulating material which forms structural load bearing elements in a constructed wall. The block (10) has cladding (12) bonded to its lateral surfaces. The cladding (12) is offset from the lateral surfaces with tie cladding (12) overhanging from the lower lateral edges, the overhanging portion abutting against the core (11) of the blocks (10) on the lower course. The core (11) has a longitudinal void (14) provided in the lower surface along its whole length and al least one vertically extending void (15), extending from the longitudinal void (14) to the upper surface of the core. Furthermore, recesses (21) are formed in the vertical edges of the core (11) and being adapted to receive elongated joint seals (22) to affect scaling of the joints between adjacent blocks (10).