Attached Link: http://www.copyright.gov/help/faq/faq-protect.html

Copyright law has been amended to determine what is & isn't covered in architecture... anything built before 1990 is not protected under current law. Point #10 at the link above explains it more fully but the salient passage is... "Copyright protection extends to any architectural work created on or after Dec. 1, 1990... Architectural designs embodied in buildings constructed prior to Dec. 1, 1990, are not eligible for copyright protection. See, Circular 41, Copyright Claims in Architectural Works"