A fire retardant structural board is provided that includes a body of natural fibrous material, a triglycidyle polyester binder, a sodium borate pentahydride fire retardant, and a sodium borate pentahydride fire retardant. The body of natural fibrous material has a weight, first and second surfaces, first and second sides, and a thickness. The natural fibrous material and triglycidyle polyester are dispersed throughout the thickness of the body. The sodium borate pentahydride fire retardant is dispersed between individual natural fibers of the natural fibrous material and throughout the thickness of the body. A sodium borate pentahydride fire retardant composition also coats at least the first surface of the body.