Determining thermal performance of spandrel assemblies in glazing systems is a challenge for design teams. Most designers rely on current building energy codes and industry standards for defining and determining performance, but the industry as a whole recognizes that these codes and standards have several shortcomings regarding spandrel thermal performance. It is important for designers to understand the purpose of the codes and standards, as well as their limitations, when determining thermal performance. In this paper, we address the challenges in estimating the thermal performance of spandrel assemblies in glazing systems by reviewing current building energy code and industry standards, performing a parametric study using two-dimensional (2-D) and three-dimensional (3-D) analysis and calculation methods, and discussing considerations for future development of calculation methods, codes, and standards to address current shortcomings.