Abstract: A modular, pre-insulated and furred structural masonry building block comprised of a basic structural masonry element of modular dimension which incorporates into its construction by entrapment through a series of interlocking dovetail-shaped grooves. First: A furring element to allow the attachment of fixtures and finishes directly to the finished wall by the simplest means, nails or screws and the like, and second: A insulating element with a vapor barrier attached thereto which provides 100 percent full face area coverage including the mortar joints between block, and further incorporates into its design an excess mortar pocket around the perimeter between the elements which will allow the edges of the individual insulating elements to butt squarely together forming a continuous thermal barrier.