Appendix: Methodology

The conclusions of this report have their foundation in a spreadsheet model that quantifies and projects the total floor space of certified and registered LEED NC, LEED CS, and LEED EBOM projects. Based on data available and the methodology described below, we calculated six floor area streams of figures -- Certified LEED NC, "Built to LEED" NC, Certified LEED CS, "Built to LEED" CS, Certified LEED EBOM, and "Built to LEED" EBOM.

2000-2008: When available, we used actual historical figures from the US Green Building Council. However, in some cases only aggregate figures were known, requiring estimates for the amount of floor space each category comprised. Using actual average floor space per project figures in specific years and categories along with the reported number of projects per year in each category allowed us to calculate annually added square footage. Finally, we used cumulative figures on LEED construction to date to work backwards and test the accuracy of our calculations. Because LEED was launched in an almost exclusively American context in its early years, the total floor area between 2000 and 2005 was predominantly -- roughly 94% on average -- comprised of US-based projects.

Since 2005, in tandem with the market's recognition of LEED as an internationally regarded and applicable standard, the number of overseas projects, and total floor space, has risen considerably. We thus took into consideration an increasing amount of floor space that comes from foreign projects (more than 20% of all LEED floor area), and subtracted an amount from our floor space figures in that has increased year-by-year. The commercial model evaluates only the environmental impacts of green buildings in the U.S.In some of our results, we applied "LEED penetration" estimates to determine accurately the impact of green buildings as a function of their share of non-green construction. To determine the market share held by LEED, we compared LEED floor space against national figures. We used 2007 Department of Energy (DOE) Buildings Energy Databook published data on building stock in 2000 and 2005, as well as projections for 2015 and 2020. From these figures, we ascertained new construction annually as a function of the implied average annual rate of growth minus a calculated floor area that had reached the end of its useful life.

Comparing the cumulative annual addition of LEED construction against cumulative new construction since 2000 thus generated a "market penetration" figure of LEED for the six streams of data. Once these numbers were obtained, it was possible to get an idea to what degree LEED has infiltrated mainstream building and whether or not it has become a robust catalyst for changing the baseline case.

2015 and 2020 Projections: Current market penetration data served as the starting point for making a best guess on the near-future trajectory of LEED. We modeled our projections on a Pearl-Reed growth curve, which is an S-curve function that trends toward an upward limit that is often used to simulate and predict technology penetration trends.