Dynamic site layout planning in construction projects focuses on identifying the location and space of temporary construction facilities on sites while considering the dynamic changes in the needs and availability of site space over the project duration. Existing dynamic site layout planning models generate layout plans of construction stages chronologically without considering their future effects whichmay lead to non-optimal or infeasible solutions. This paper presents the development of an Approximate Dynamic Programming (ADP) model that is capable of globally optimizing dynamic site layout plans of construction projects in order to minimize overall site layout costs. The developed model is equipped with the look-ahead capabilities of ADP to consider the future effects of site layout decisions in early stages on layout quality and feasibility in future stages. An application example is analyzed to illustrate the use and capabilities of the developed model in generating global optimal solution for dynamic site layout planning of construction projects.