The IgCC Sustainable Building Technology Committee concluded that the needs of the environment, the jurisdictions adopting the IgCC, building owners and design teams would be best served by a methodology for calculating building energy use that, as closely as possible, reflected the actual energy use of the building and the emissions resulting from that energy use. This presentation will discuss the process and rationale that led IgCC to adopt the zEPI scalar as the energy efficiency compliance metric and calculate source energy and regional emissions based on the EPA e-GRID database of power generation environmental characteristics.