In this study, we try to propose the system selecting the combination of building materials to reduce environmental loads (CO_2 exhaust, costs and waste) with using GA(genetic algorithms). The estimation of a wooden house in this system is smaller than one in general. And some houses which have similar value are made from different materials each other. So we can get the better answer and find one that we haven't got empirically yet and we can show the usefulness of this system.