A foundation system includes metal framing members that support a reinforced, lightweight, dimensionally stable cementitious panel. The foundation system is non-combustible, water durable, mold and rot resistant, and termite resistant. The panels employ one or more layers of a continuous phase resulting from the curing of an aqueous mixture of inorganic binder, for example, calcium sulfate alpha hemihydrate, hydraulic cement, an active pozzolan and lime. The continuous phase is reinforced with glass fibers and contains lightweight filler particles, for example, ceramic microspheres.