Mid-twentieth-century architecture imposes unprecedented challenges onto the field of historic preservation. These problems are placing a strain on the theories, charters, and guidelines developed over the years to guide preservation efforts. As a result, there are collective calls for a reevaluation of the field’s principles. However, an in-depth understanding of why traditional preservation methodologies warrant retooling is missing from this overarching conversation. This thesis analyzes a select number of longstanding preservation doctrines to determine whether or not they are adequate for preserving post-war architecture. In order to assess the field’s traditional theories, charters, and guidelines, this thesis uses the Philadelphia Police Headquarters, also known as the Roundhouse, as a case study. This building presents a range of problems that similarly affect other mid-century buildings. Throughout the evaluation, each doctrine proved to be insufficient for resolving the challenges hindering the Roundhouse’s preservation. In response to these findings, this thesis offers a new methodology to help guide preservation efforts of post-war architecture, with flexibility as a fundamental attribute.