Posted by Paul Malo on September 18, 2002 at 13:26:17:
In Reply to: pro BRUTUS et aliae posted by d on September 18, 2002 at 12:25:51:
The triangle is the most stable form, 2-dimensionally, and the tetrahedron is the most stable 3-dimensional form (as Bucky used to preach). The diagonal may have gone out of fashion for roofs, given the Modernists' strange (inexplicable to me) preference for cubic forms and leaky flat roofs, but that is mere style. You can be sure than engineers still understand the value of the diagonal.
One of the traits of the Modern style, as this instance suggests, was less structural functionalism than "structural exhibitionism"--the display of audacity in doing the apparently impossible. Cantilevers, of course, were one of the features of anti-gravitational levitation that so enamored modernists--but the "upside-down" strategy of the Villa Savoye or the Boston City Hall, putting the visually heaviest elements on top, carried by visually weaker elements, was another device.
The gable roof is really a far more rational form structurally, because of its triangulation, than the modernist flat roof. A simple gable roof, when tied across the eaves, is really a truss.
You can span say 24 feet using 2x4s by this arrangement, whereas a flat roof on the same span would require something like a 2x12 and probably then would deflect visually to an unsatisfactory degree.
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