membership. Less than twenty buildings were certified under LEED 1 before March 2000, and LEED 2 had certified just over 25 to Feb. 2003. But hundreds of buildings have been registered in the program since 2001, and LEEDs sudden popularity seems to be changing the face of mainstream commercial building in the US. In 2002, LEED certified buildings accounted for almost 5 percent by floor area of new commercial construction in the US. Newly registered projects include numerous federal government and even US military structures, and the ranks of green building professionals, previously a small group of committed activists, are being swelled by a new wave of LEED-certified architects and engineers in mainstream firms. LEED seems also to be changing the Canadian construction industry, as initiatives are being undertaken to implement LEED or LEED-compatible assessment systems here (Trusty & ATHENA Sustainable Materials Institute, 2002). Previously the UKs BREEAM had been a bigger influence on building assessment in Canada. LEED like BREEAM is market-oriented and voluntary, but in structure is quite different. BREEAM, like the assessment framework of the Green Building Challenge, is more of a pure assessment systemwith an emphasis on tabulating environmental loadings. The LEED system is more of a design-support tool, based on a checklist in five key areassustainable sites; energy and atmosphere; water use; materials and resources; and indoor environmental quality. There are weighted credits for each area, but the developer has a choice as to what areas to seek credit for. Buildings get ratingsfrom highest to lowestof platinum, gold, silver, bronze, and basic-certified, depending on how many credits they accumulate; but this is more an incentive system than a measure of environmental impact.