Can you imagine any of these buildings with a sill? Would you accept having all the ledges covered by dirt? No.
The solution is easy: consider the horizontal plane at the bottom of the window as a roof, and then decide whether it is a “flat roof” so water goes in, or a “pitched” roof so water is directly driven out.
We tend to think that tradition, the logical, easier way to do it, will lead to a “pitched roof” solution and so a sill that is inclined outwards. These SANAA’s, Libeskind’s, and Graber-Pulver’s solutions may look flighty, but have a look to this old traditional Gallegan window!
There’s water inside! Of course, this is a double-window with a drained cavity in-between. Old wooden windows are not so effective regarding water tightens and so, in really rainy weather, arise these clever solutions.
Find the two little holes in the stone at the bottom of the window, that's where water exits; and find the entrance, in the last picture, at the corner where the sill meets the jamb.
