An extruded composite building material comprising a thermoplastic resin material, a mixture of additive materials, and a cellulosic material, wherein the thermoplastic resin material, the mixture of additive materials, and the cellulosic material are blended into a composite material, wherein the composite material comprises between 50% to 90% cellulosic material by weight, and wherein the blended composite material is extruded to form the extruded composite building material.