A non-combustible shear wall system for construction comprising: screw fasteners; a vertical shear diaphragm fastened to a light gauge cold rolled metal frame by the screw fasteners, the vertical shear diaphragm comprising a reinforced, lightweight, dimensionally stable cementitious panel and the framing comprising metal studs; the panel having a density of 1.04 to 1.44 g/cm 3 (65 to 90 pounds per cubic foot) and capable of resisting shear loads when fastened to the framing and comprising a continuous phase resulting from the curing of an aqueous mixture comprising, on a dry basis, 35 to 68 weight % reactive powder, 23 to 49 weight % lightweight filler, and 5 to 17 weight % alkali-resistant glass fibers, the continuous phase being reinforced with glass fibers and containing the lightweight filler particles, the lightweight filler particles comprising ceramic microspheres and optionally, at least one member selected from the group consisting of glass microspheres, fly ash cenospheres and perlite, the lightweight filler particles having a particle specific gravity of from 0.02 to 1.00 and an average particle size of about 10 to 500 microns (micrometers), wherein the reactive powders comprise, on a dry basis, 45 to 65 wt % calcium sulphate alpha hemihydrate, 25 to 40% wt % hydraulic cement, 0.75 to 1.25 wt % lime and 10 to 15 wt % of an active pozzolan comprising silica fume, wherein the system having a 9-19 mm (3/8-3/4 inch) thick structural cementitious panel panel mechanically fastened to laterally braced said light gauge cold rolled metal frame when tested according to ASTM E-72 has a nominal wall shear capacity of 521 to 1786 kg per lineal meter (400 to 1200 pounds per linear foot), and wherein the system having a 12.7 mm (1/2 inch) thick SCP panel fastened to laterally braced said light gauge cold rolled metal frame when tested according to ASTM D-1761 has a dry lateral screw resistance of 159 to 249 kg (350 to 550 pounds). screw fasteners; a vertical shear diaphragm fastened to a light gauge cold rolled metal frame by the screw fasteners, the vertical shear diaphragm comprising a reinforced, lightweight, dimensionally stable cementitious panel and the framing comprising metal studs; the panel having a density of 1.04 to 1.44 g/cm 3 (65 to 90 pounds per cubic foot) and capable of resisting shear loads when fastened to the framing and comprising a continuous phase resulting from the curing of an aqueous mixture comprising, on a dry basis, 35 to 68 weight % reactive powder, 23 to 49 weight % lightweight filler, and 5 to 17 weight % alkali-resistant glass fibers, the continuous phase being reinforced with glass fibers and containing the lightweight filler particles, the lightweight filler particles comprising ceramic microspheres and optionally, at least one member selected from the group consisting of glass microspheres, fly ash cenospheres and perlite, the lightweight filler particles having a particle specific gravity of from 0.02 to 1.00 and an average particle size of about 10 to 500 microns (micrometers), wherein the reactive powders comprise, on a dry basis, 45 to 65 wt % calcium sulphate alpha hemihydrate, 25 to 40% wt % hydraulic cement, 0.75 to 1.25 wt % lime and 10 to 15 wt % of an active pozzolan comprising silica fume, wherein the system having a 9-19 mm (3/8-3/4 inch) thick structural cementitious panel panel mechanically fastened to laterally braced said light gauge cold rolled metal frame when tested according to ASTM E-72 has a nominal wall shear capacity of 521 to 1786 kg per lineal meter (400 to 1200 pounds per linear foot), and wherein the system having a 12.7 mm (1/2 inch) thick SCP panel fastened to laterally braced said light gauge cold rolled metal frame when tested according to ASTM D-1761 has a dry lateral screw resistance of 159 to 249 kg (350 to 550 pounds).