KieranTimberlake (Philadelphia) is known for LEED platinum certified projects such as the Yale University Sculpture Building and Sidwell Friends Middle School as well as experimental structures like Loblolly House and Cellophane House. For many years the office has been interested in issues of sustainability. Thomas Madlener talked to James Timberlake and Richard Maimon about recent developments in sustainable architecture in the US, and how it will evolve in the future.