AbstractThe accuracy of building energy needs estimation is one of the most important challenges of building energy research. The boundary conditions have a significant impact on building energy performance and studies in the literature demonstrated that considering the uncertainty in input parameters is essential to achieve a more realistic energy model. One of the quantities defining the boundary condition that is most subject to uncertainty- is the incident solar radiation on the building envelope, composed ofdirect, diffuse and ground reflected radiation. Trees, adjacent buildings and street optical-radiative properties affect the short-wave radiation incident on building facades.This PhD research, will look for a framework to quantify the uncertainty of incident radiation on the building envelope to provide a more accurate representation of radiative exchange within an urban canyon environment. Among the mentioned factors, the uncertainty quantification of the ground reflectance parameter is discussed in the present paper . The reliability of the performance estimation in two different shading scenarios is assessed based on the outputs of the uncertainty quantification. The first scenario is an on/off controlled shading based on the incident solar radiation. After this analysis, designers may find an optimal schedule for the presented shading system, depending on the building use. The second scenario, proposes a fixed shade, highlighting the importance of uncertainty in ground reflected radiations while assessing the reliability of a shading design.Key-words:Uncertainty, solar incident, shading devices, Performance gap.