The most common approach for calculating thermal resistance (R-value) of building facades is based on the additive method, where material components of the facade in sectional view, their relative thickness and thermal conductivity are considered. However, in order to account for thermal bridging caused by framing, area-weighted approach should be used to determine more accurate R-value. This approach also considers plan view of building facade, and the properties of framing components. The main objective of this research was to investigate the effects of facades’ thermal resistance (additive vs. area-weighted R-values) on buildings’ energy performance.

Research methods included data collection, modeling, simulations and comparative analysis of results. An existing Campus Recreation Building, located at the University of Massachusetts Amherst, was used as a case study building. First, the original construction documentation was reviewed to create a 3D model in Revit. Facade material components and specifications were used to determine properties of the opaque facade system, consisting of a brick cavity wall with steel stud framing. R-values for this facade system were calculated using additive and area-weighted methods. Then, a building energy analysis simulation program Green Building Studio was used for analysis, where one energy model was created to analyze the impacts of two different R-values on the overall energy consumption of this building. Other inputs, such as building geometry, occupancy schedules, glazing materials, etc. were identical in both models. Energy modeling results were compared to actual energy consumption data, collected over a period of one year. Simulation results showed that energy consumption was 2.5% higher when area-weighted R-value was applied.