Water outside / Water inside (120)

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Water outside / Water inside (120)

Could you imagine any of those buildings with a sill? Would you admit to have all the ledge covered by dirtiness? For both: No

As easy as considering this horizontal plane at the bottom of the window as a roof, and then, deciding whether it is a “flat roof” -and so water goes in-, or a “pitched” one -water is directly driven out-. 

We are tended to think that tradition, the logical and easier way to do it, will lead to a "pitched roof" solution, and so, an inclined outwards sill. Those SANAA's, Libeskind's, and Graber-Pulver´s solutions may look like flighty, but, have a look to this old traditional Gallegan window!!!

Water inside!!! Of course, it is a double-window with a drained cavity in-between. Not really effective watertightness mechanisms in old wooden window frames, plus a really rainy weather, leads to those 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.