The Hirshhorn Museum, opened in 1974, is a landmark of Brutalist architecture and serves as the Smithsonian Institution’s museum of contemporary and modern art. In its time, the building, a squat concrete donut, nearly windowless on the exterior and elevated over a courtyard by four massive piers, was a controversial addition to a landscape of stately and monumental “traditional” museums. After more than forty years in service, the building is experiencing performance issues that are part and parcel of its 1970s’ technology: Its energy performance is poor by contemporary standards, and the mechanical humidification required to preserve its collection causes wintertime condensation on building enclosure components. While these issues can be ameliorated or resolved with contemporary technology, the Hirshhorn’s peculiar geometry and immutable architecture place limits on the addition of contemporary materials and equipment. Potential trade-offs include appearance changes, disruption of the collection, reduction in usable space and, of course, cost. The Smithsonian Institution is dedicated to preserving this architectural landmark and is assessing options for performance upgrades to the building but requires quantitative as well as qualitative information to support its decision-making. Using the building science–based options analysis for the Hirshhorn’s enclosure as an example, the paper will work through a technical analysis and decision-making process, including: identification of required enclosure repairs to address performance issues; comparison of building science modeling tools to determine the cause of condensation and its extent, and correlation with field observations; analysis of building enclosure alterations to improve energy performance; establishment of minimum improvements to resolve wintertime condensation; and qualitative assessment of air and thermal barrier improvements and their potential to reduce energy consumption.