Copyright Claims in Architectural Works: (United States Copyright Office)

Cornell University: Copyright Term and the Public Domain in the United States The law changed in 1990, so when the building was built can determine if the actual *building* is protected by copyright or not. Sometimes only the plans and drawings are protected or the building itself, the plans, and the drawings are protected by copyright. 
*Certain famous buildings, such as the Empire State Building: can also be protected by trademark, which is a different kind of intellectual property than copyright.