Nancy Keates in the Wall Street Journal, use the link to bypass paywall:

Allison Paschke, an artist, and John Danskin, a computer engineer, needed some space from each other. The couple, who had been married for more than two decades and raised two kids, found themselves squabbling over lots of small things, but they didn’t want to get divorced. So in 2006, they sold their three-story house in Cranston, R.I., and bought a 4,300-square-foot loft in the old jewelry district of downtown Providence for $600,000. Then they went about dividing the loft into two connected but utterly distinct living areas, each with its own bedroom, kitchen, dining area and workspace.