Molded concrete building blocks consisting of three block walls and block webs so located as to provide an increased path through the width of the block to reduce transmission of thermal and acoustic energy. The blocks may incorporate features, e.g., male projections and female recesses or an offset inner wall, so that mortar may not be required for assembly. The blocks may be configured so that interior apertures may be vertically aligned when the blocks are assembled in courses, providing adaptability to structure enhancing reinforcement and insulation materials, and to interior wall installation of wiring and plumbing.