A rectilinear floor is a polygonal floor all of whose edges meet at right angles. Rectilinear floors are commonly found in buildings. This study proposes a new genetic algorithm for beam-slab layout design of rectilinear floors. To begin with, a coding scheme that can efficiently represent beam-slab layouts of rectilinear floors as binary chromosome strings is developed. After that, an optimization problem representing the beam-slab layout design problem is defined. This optimization problem is then solved by a genetic algorithm specially tailored to the problem. To demonstrate the validity of the proposed algorithm, it is used to design beam-slab layouts of several floor plans, some of which are taken from existing buildings. The obtained results show that the beam-slab layout design task, which is highly heuristic, can be satisfactorily performed by computers. © 2010 Elsevier Ltd.