This paper proposes an interactive goal-based method for designing day lit buildings. The lighting simulation tool which supports this process is a hybrid global illumination rendering method which efficiently computes annual daylighting metrics. The goal-based method uses a knowledge base populated using a set of previously completed simulations that quantify the effects of various façade design modifications. The knowledge base guides a simple algorithm over an iterative design process. The current knowledge base includes information about window size, shape, location on the façade, and simple shading devices. Three case studies are given in which this iterative optimization method was applied; all resulted in improved daylighting performance.