Minerva Ketter lost her home gently, over time, as her listing house sank around her. The ceiling let in rain, the floors let in light, and the front porch gradually sagged until it was almost in the front yard. Finally, she had to abandon her ramshackle house and move in with her father next door.
Then one day last spring volunteers swarmed like carpenter ants over the Hartsville, S.C., neighborhood, slapping paint, hammering walls, shingling roofs, shoring up porches. By day's end, Ketter's house, like 37 others in town, had been delivered from ruin. "I didn't know something like this could...