Much has been made of the fact that, in creating perhaps the film world's most famous stunt, Buster Keaton allowed a wall to fall on him in Steamboat Bill, Jr. without the benefit of rehearsing the trick. He went out there, measured off the distance, then stood in front of a house whose entire front section collapsed over him, with the cameras rolling. They got one take, just like the famous shot of the tidal wave of nuclear waste in the Radioactive Man movie.
But that's not so odd to me. What's odd is that Keaton used a full-weight wall, one that would have crushed him if he had missed his mark. This entire sequence of the movie, with a cyclone literally ripping the town apart, clearly relies on many lightweight, breakaway buildings being torn from their moors and scattered to the winds. So why not use one of those for the building falling on Buster? I don't know; maybe the added heft gave it a little bounce when it hit the ground around him.
In case you're wondering what I'm talking about, here's some of the cyclone sequence from Steamboat Bill, Jr. (I don't believe this music is original to the film.) The canonical house drop happens at about 2:15.