The layout of a construction site has a significant impact on the overall productivity and cost effectiveness of a construction project. This paper presents the work done in applying genetic algorithms towards the optimization of the layout of the temporary facilities on a site. The genetic algorithm technique combines survival of the fittest among string structures with a structured yet randomized information exchange to form a powerful search technique. Unlike traditional optimization techniques, the assumptions required to use this technique is not restrictive. The key issue in developing genetic algorithm based model for the site layout problem was the formulation of a string representation of spatial information. Other issues in developing the model were developing a fitness function and selecting strategies for selection, and generation. Initial tests of the model show that the approach gives workable layouts within reasonable time.