Book excerpt: The worldwide use of building envelopes in steel and glass is one of the characteristic features of modern architecture. Many of these pre- and post-war buildings are now suffering severe defects in the building fabric, which necessitate measures to preserve the buildings. In this endeavor, aspects of architectural design, building physics, and the preservation of historic buildings play a key role. Using a selection of 20 iconic buildings in Europe and the USA, the book documents the current technological status of the three most common strategies used today: restoration, rehabilitation, and replacement. The buildings include Fallingwater House by Frank Lloyd Wright, Farnsworth House by Ludwig Mies van der Rohe, Fagus Factory and Bauhaus Building by Walter Gropius.