Abstract: A building wall utilizes a pair of cementuous blocks having a thermally insulating space therein-between The blocks are fastened together by tie rods whose ends are secured in the spaced apart blocks. The portion of the rods extending between opposed lateral surfaces of the blocks have a portion of the length thereof formed into a "V" shape for concentrating water condensation trapped in the space between the blocks permitting the condensation to fall freely downwardly in the space. The blocks may be fabricated in conventional modular sizes or may be precast into any desired size such as an entire wall. Devices are provided for centering and locking together sets of blocks utilizing a tongue in groove arrangement in opposed horizontal marginal edges of one or both blocks.