In this paper, practical optimal design method is proposed based on genetic algorithm for determining placement and cross-section of bearing wall, beam and horizontal brace of steel residential house. Employed building system has discrete choices for member sections, and member placement at 150mm unit. With this system, rational design is required in high design freedom. Especially, it is difficult to determine beam placement because of complicated constraints on the beam placement around a stairwell or under a roof strut. However, few methods have been proposed considering such problems. The objective of this paper is to obtain practical solution in realistic time considering design constraints for various building plans.
