A concrete building block for masonry block walls is formed with first, second and third spaced parallel rectangular face shells, where the second face shell is intermediate the first and third face shells. First and second vertical end cross webs connect the first and second face shells and first and second spaced intermediate vertical cross webs connect the second and third face shells. Insulating inserts include end protrusions extending outwardly at the top edge thereof to fit into notches of the cross webs and include cutouts to accommodate mortar crumbs. The inserts further include longitudinal notches along the entire bottom edges and longitudinal notches along the entire top edges wherein said longitudinal notches along a bottom edge are dimensioned to mate with longitudinal notches along a top edge of neighboring ones of the insulating inserts creating an overlap that serves to (i) insulate against temperature transfer and (ii) provide a sound barrier.