For decades, architectural sustainability was dominated by operational performance. Better insulation, efficient mechanical systems, photovoltaic panels, passive solar strategies, and high-performance envelopes became the principal instruments for reducing environmental impact. Those measures remain important, but they no longer describe the entire carbon problem. A building can perform efficiently in operation while carrying an enormous historical carbon burden embedded in its concrete frame, steel reinforcement, glass, aluminum, masonry, finishes, foundations, and infrastructure. Once these materials have been manufactured, transported, assembled, and incorporated into a structure, their associated emissions cannot simply be erased by installing efficient equipment. This is where the concept of material memory becomes architecturally significant. Existing buildings contain not only physical material but also the emissions already invested in producing that material. Retaining a structural frame therefore represents more than preservation. It can function as a form of carbon avoidance.