Preserving, restoring and improving the performance of the built environment is the primary purpose of the firm of Douglas J. Lister, Architect. Few buildings in New York City were designed to have a life span of more than forty years. Yet many large buildings in Manhattan are twice this age. Maintaining these buildings economically requires a combination of scientific investigation, historical information and architectural sensitivity. All buildings have to perform. Buildings protect their occupants from the infiltration of temperature, water, air and sound. New technologies and the resurgence of old technologies have enabled us to both improve our performance and preserve the original character of older buildings. Performing maintenance and restoration projects in occupied buildings requires continual communication with building management, occupants and contractors, Most exterior work requires a temporary invasion of privacy of many occupants. It is critical that the occupants understand both the necessity for repairs and the length of the project.