Krier identifies the leading error of modernism as that introduced by Le Corbusier, Gropius, and Ludwig Mies van der Rohe: separating load-bearing and outward-facing parts. Once buildings become curtains hung on invisible frames, all of the understood ways of creating and conveying meanings lose out. Even if the curtain is shaped like a classical facade, it is a pretend facade, with only a blank expression.
Usually, however, it is a sheet of glass or concrete panels, without intelligible apertures. The building itself is hidden, and its posture as a member of the city, standing among neighbors and resting its weight upon their common ground, is meaningless because unobservable. All relation to neighboring structures, to the street, and to the sky, is lost. The form conveys nothing beyond the starkness of its geometry.
The curtain-wall idiom has other negative effects. Buildings constructed in this way are both expensive to maintain and of uncertain durability; they use materials that no one fully understands, which have a coefficient of expansion so large that all joints loosen within a few years, and which involve massive environmental damage in their production and in their inevitable disposal within a few decades.
Modernist buildings are health catastrophes: sealed environments, dependent on a constant input of energy, and subject to the “sick-building syndrome” that arises when nobody can open a window or let in a breath of fresh air. Moreover, such buildings use no architectural vocabulary, so that one cannot “read” them as one does classical buildings. The passerby experiences this as a kind of rudeness. Modernist buildings exclude dialogue, and the void that they create around themselves is not a public space but a desertification.