The building blocks have tongued and groove connecting supporting faces. Each groove (10) and each associated tongue (2) has recesses and corresponding projections (3). The filler openings are formed by a central opening (4) and semi dish-shaped end openings (5) arranged in opposite abutting faces. The projections and recesses extend towards the side of the tongue and groove resp. Seals are arranged between the supporting bearing faces. The seals can be made of a strip extending over one layer of blocks placed side by side. Seals can be provided between abutting faces of the blocks.
