Abstract: The building block comprises spaced apart outer and inner concrete walls and a pair of tie members for interconnecting these two walls. Each tie member has a first T-shaped end embedded into the concrete of the outer wall. A solid and cubic body is made of wood and is fastened to a second end of each tie member. For that purpose, each body has a hole therein, and the second end of each tie member is forked to define first and second branches embracing a portion of the body and having respective free ends bent to penetrate the hole through its two ends, respectively. The cubic body defines edges having a length equal to the thickness of the inner wall, and it is embedded in the concrete of this inner wall with a surface thereof exposed on the two sides of the latter wall. Nailing and/or screwing through the cubic body is therefore enabled from the outer side of the inner wall with the nails and/or screws extending in the space between the outer and inner walls.