Evaluating the Sustainability of New Construction Projects over Time by Examining the Evolution of the LEED Rating System

In 1998, the U.S. Green Building Council (USGBC) developed the Leadership in Energy and Environmental Design (LEED) program to provide a standard form of evaluation for sustainability in building design and construction. Since its inception, LEED has undergone seven significant revisions, wherein the expectations needed to achieve the desired certification level were clarified and updated. The reasons for these updates are varied and include the recognition of new technologies and materials, the application of more stringent energy standards, and the recognition of differences in building types. However, the perception within the architecture, engineering, and construction (AEC) industry is that higher certification levels are more challenging to obtain in each subsequent version of LEED. For example, projects receiving a Gold certification under LEED 2.1 may only qualify for a Silver certification under LEED 3.0. The goals of this paper are to review changes in LEED over time and to empirically test this perception. Direct comparisons of the text of the credit requirements were performed between LEED versions (v) 2.1, v2.2, and v3.0 on a credit-by-credit basis. The comparison revealed ten different categories of changes between versions. From this comparison, conversion matrices were developed to allow a project scorecard from an older version of LEED to be converted to a newer version. To address uncertainty resulting from changing the level of detail in the information submitted on project scorecards, both strict and interpretative versions of these matrices were developed. These matrices were then applied to a sample of LEED-certified building projects, drawn using a stratified random sampling procedure from the publicly available USGBC database. The strata were separated first by LEED version (e.g., v2.1, v2.2, and v3.0) and then by certification level (e.g., Certified, Silver, Gold, Platinum). After converting the project scorecards from this sample, qualitative and correlational analyses were performed to test the hypothesis that LEED scores increase over time. The results show that in both strict and interpretive transformations, LEED scores show a slight to moderate increase in points over time