A masonry cavity wall structure includes a cast-in-place reinforced concrete structural wall member erected between and in confronting engagement with the outer side of a first, inner masonry wythe and the inner side of an outwardly spaced-away, upstanding wall of rigid insulation panels supported by wire tie members in embedded engagement in the mortar joints of the inner wythe, the inner wythe and tie-supported insulation panels also being used during construction of the cavity wall to provide the supporting concrete formwork for the poured structural wall member. A second, outer veneer wythe is erected a predetermined spaced distance outwardly from the insulation panels and forms an airspace cavity therebetween, the wire tie members also engaged in the mortar joints of the second, outer wythe whereby to structurally tie the masonry cavity wall together. The placement of the cast-in-place reinforced structural wall immediately adjacent the inner wythe and inwardly of the insulation provides maximum thermal mass qualities of the cavity wall construction.