Insulating the exterior wall of an historic property can have the benefits of increasing thermal comfort for occupants as well as reducing energy use for heating and cooling. Concerns expressed by preservationists that insulation can lead to the degradation of the building structure or its historic fabric. Using the Park Inn Hotel, an early twentieth century commercial property designed by Frank Lloyd Wright, the application, feasibility, ramifications and potential benefits of applying insulation to the exterior wall was studied. Analysis for insulation includes evaluation of the historic characteristics, construction of the exterior wall, heat loss calculations, and how moisture will be transported through the wall. It was found that the key to determining if the exterior wall of a historic building can be insulated successfully without damage to the historic characteristics of the building or to the building itself, is in understanding how the building was designed and how it deals with moisture. With a thorough understanding of these elements, one can ascertain if insulating the exterior wall of his/her historic building is appropriate. / Department of Architecture