One building form that typifies the explorations of Postmodernism is the traditional gable roof, in place of the iconic flat roof of modernism. Shedding water away from the center of the building, such a roof form always served a functional purpose in climates with rain and snow, and was a logical way to achieve larger spans with shorter structural members, but it was nevertheless relatively rare in Modernist buildings. However, Postmodernism's own modernist roots appear in some of the noteworthy examples of "reclaimed" roofs. For instance, Robert Venturi's Vanna Venturi House breaks the gable in the middle, denying the functionality of the form, and Philip Johnson's 1001 Fifth Avenue building in Manhattan advertises a mansard roof form as an obviously flat, false front. Another alternative to the flat roofs of modernism would exaggerate a traditional roof to call even more attention to it, as when Kallmann McKinnell & Wood's American Academy of Arts and Sciences in Cambridge, Massachusetts, layers three tiers of low hipped roof forms one above another for an emphatic statement of shelter.