ASHRAE 90.1. LEED 2009. IGCC. As standards, rating systems, and codes for sustainable building proliferate, it's important to know how they differ and overlap, and how they impact architects. At a Friday session, "Green Building Codes, Standards and Rating Systems--A Comparison," speakers explained the distinctions between these tools and described their scope. A standard, said engineer Kent W. Peterson, represents an industry consensus on requirements. A standard can be referenced in a code, which when adopted by a government is enforceable by law. Codes, standards, and rating systems can complement one another to drive the market for sustainable building. Two speakers talked about the emerging relationship between green codes and LEED, in which LEED can serve as the "ceiling"--an ever-more-rigorous rating that market leaders will strive to achieve--while codes are the "floor," setting a more sustainable baseline.