This paper presents the results of a combined analytical, computational, and experimental study of the key parameters for selecting affordable materials and designing for thermal comfort in passive solar buildings. The heat transfer across the walls of buildings is modeled using a simple heat diffusion model. In this way, the passive heat storage from the sun (passive solar) and the heat load from internal heat sources are stored in the walls of buildings that provide internal cooling during the day and internal heating at night. The simple analytical model of heat diffusion is used to identify the merit indices for the optimization of affordable passive solar performance. The time dependence of wall/internal temperature is then simulated using a simple finite difference model. The results from the analytical model and finite difference model are validated by conducting temperature measurements in two affordable housing complexes in Egypt. The implications of the results are then discussed for the design of thermal comfort in affordable housing.