As interest in sustainable design increases, many methods have been suggested to develop an integrated sustainable design process. However, due to the lack of a scientific procedure using parametric tools for an objective evaluation, it is difficult to move forward with integrated sustainable design. In addition, the design priority of the indoor environment is still relatively low because of the score composition of the green-building certification system. Therefore, this study aimed to develop a simulation tool and method to help apartment-complex layout planning in urban contexts by focusing on the indoor daylight environment. In particular, Korean cities are densely formed with high-rise buildings in a small area, so the Korean Building Act has complicated provisions to reduce overshadowing between buildings. To reduce unnecessary wasted time while checking these complicated regulations, a simulation was used to automatically check building offsets. Galapagos, a component of Rhino-Grasshopper, was used to apply a genetic algorithm that discovered optimized results. A standard flat-type apartment complex in Seoul was analyzed with the developed tools in order to compare the existing plan with an optimized layout. The results of the simulation and the suggested analysis methods can help in the initial planning stages of an integrated sustainable design in a high-density city with a temperate climate. This allows architects to utilize the proposed results or use them as a reference for further modification and design.