The current state of the art for calculating radiative flux transfer in urban spaces assumes the urban context to be entirely comprised of uniformly diffusing surfaces. In reality, modern of urban contexts feature a mix of specular, semi-specular, and diffusing surfaces. In this study, the authors propose a new framework for simulating radiative transfer that facilitates a comparative evaluation of different surface materials on radiative flux transfer. Utilizing a prototypical street canyon model, the study quantifies the variations in radiative flux distribution caused by specular and diffusing surfaces under various sky conditions. Results from simulations using historical weather data and geographical inputs indicate that specular surfaces significantly alter the distribution of radiant energy, particularly under direct sunlight conditions, thus challenging the prevalent assumption of uniform diffusion in urban radiation models.