[freebeard]

While you think in terms of conventional attics, I think in terms of geodesic dome, with minimal material composition. Like aluminum plating weather shell with a tensioned fabric or foil inner shell.

Also I wonder whether the foamed aluminum can pass air or Nitrogen gases. If so it might be an ideal material to cast nose cones for atmospheric reentry.

edit:
To be clear, the space between the inner and outer shell replaces the attic. But it's a dynamic system (down on the shady side, up on the sunny side) instead of a stagnant pool. Don't get me started on engineered roofing trusses.