Abstract: An insulating molded plastic building unit comprises a rectangular parallelopiped without a rear wall. One or more alignment bosses extending upwardly and outwardly from an upper wall of the building unit are equidistantly spaced from a front face and a side face thereof to cooperatively align with alignment sockets of and automatically space superimposed building units. Each building unit has vertical and diagonal webs for structural reinforcement thereof. Cavities within each building unit can be filled with insulating material to enhance the insulating characteristics thereof. A plurality of the building units are laid in courses with joints formed therebetween with waterproof adhesive.