The reuse and retrofit of existing buildings are important tools for mitigating global warming. By some estimates, it can take up to 80 years for a new energy-efficient building to overcome the climate-change impacts created by its construction. However, greening existing buildings, especially historic ones, presents special challenges. Strategies like window replacements or recladding can improve thermal performance, but may be at odds with the structure’s character if not carefully executed. And although new mechanical systems can help an older building meet the comfort expectations of current occupants, such systems are often difficult to insert within historic fabric. Join our panel of experts as they discuss these issues and identify strategies for the implementation of energy-efficient and historically sensitive building renovations.