Mr. Douglas plays the music he likes in his space; Ms. Lanahan plays what she likes in hers. They eat and sleep in Ms. Lanahan’s house and watch the news after dinner in her living room, but tend to watch movies in his space. During the day, they often communicate by phone.

There were a number of factors that led to this unusual arrangement, but high on the list was the need for a room of one’s own.

“We definitely wanted independent space,” Ms. Lanahan said. “He could have had the apartment. That would have connected us completely. We could have opened up a wall. I think he just wanted a place that was a lot like the one he was leaving, and his own domain. This is so similar to what he had in the country, it’s phenomenal. We built the studio to be just like his big room, minus the wall he used for a kitchen.”

Mr. Douglas, who wears a ponytail and has an unsettling resemblance to the actor Nick Nolte, disputes this. This place is not an exact replica, he says. The furniture is not precisely where it used to be. But yes, he admits, he did not buy any new furniture, and it is very similar. He also says that many seem to covet their bridge.

“When it was built, so many people would say: ‘I wish we had a house like this. It would be so great,’ ” Mr. Douglas says.