a housing module which is formed as a box - beam structure , and has sufficient rigidity and strength so that it can be used to span distances of relatively great length . the housing unit is able to be prefabricated and can be readily transported without the need for additional support or stiffening members to prevent damage from excess flexure . further , the unit can be simply put in place on site without any additional stiffening or strengthing members . in addition , the units can be stacked one over the other , thus greatly increasing their flexibility to the architect .