Abstract: In a building wall assembly including an outer veneer wall, a series of laterally spaced studs, an upright laterally extending lower wall board spanning the studs and a laterally extending upper wall board spanning and secured to the studs and overlying the lower wall board, with the wall boards spaced from the veneer wall, a unit moisture reflector flashing strip of a resilient material having laterally extending mount, reflector and sealing portions, with the mount portion underlying the lower edge of the upper wall board, bearing against and secured to the studs, with the deflector portion extending angularly downward and outwardly of the lower wall board and with the sealing portion against the lower wall board across its width.