Solutions of wood fireproofing salts drip from the roof into the Arts and Industries Building of the Smithsonian Institution. This has occurred on clear sunny days in the spring and early summer since the present roof was installed three years ago. The construction of the roof, the materials used and the local environmental conditions that have caused this unusual phenomenon are described. The techniques used to measure the environmental conditions within discrete layers of the roof are explained. The measurements have not yet followed the roof through its annual cycle, but proposed is a mechanism based on data gathered so far.