Energy Codes and Standards: Do They Reflect Best Practice in Building Envelope Performance?

Abstract

Energy codes and standards allow multiple paths for compliance. This paper addresses the prescriptive approach only, which stipulates minimum R-values of building enclosure insulation, fenestration thermal performance requirements, and maximum building envelope air leakage rates. Recent changes within energy codes and standards commonly reflect a “more is better” strategy regarding building envelope performance (e.g., wall and roof insulation). However, is this a sound strategy due to the diminishing energy savings as the building envelope performance improves (e.g., increasing minimum R-values)? This paper considers recent trends in energy codes and standards in the context of an energy modeling case study of an existing office building. The paper will discuss the results of parametric studies on a validated building energy model with different roof insulation minimum R-values, as well as building envelope air leakage rates and window glazing types. The case study building is an 86,400 ft2 single-story office building located in Climate Zone 5 (near Boston, MA) with a recently renovated building envelope that included new roofing, wall cladding, and windows. This building’s energy model was calibrated by incorporating data from a quantitative whole-building air leakage test, an on-site weather station, and metered energy consumption of electric and mechanical systems. The paper examines the following variables with respect to the predicted heating, ventilation, and air conditioning (HVAC)-related energy consumption: roof insulation minimum R-values, building envelope air leakage rates, window glazing types (e.g., single-, double- or triple-pane glazing, low-E coating types), and window-to-wall ratios. Finally, this paper compares the cost implications of some of these variables. While the lessons learned from this study can be applied to new construction, the results of this study are more applicable to renovations of existing buildings and their envelope systems.