He started his company in the mid-1980s, and today it has 16 employees and clients like Armani Exchange and De Beers Jewellery.

Ms. Zielinski, who is 54, grew up in Michigan. School didn’t interest her much, she says; she wanted to get out and work. She did a number of jobs, like cleaning house and bartending. She and Mr. Zielinski met after she moved to Pittsburgh. They married in 1985, raising her children from her first marriage, Melissa, now 33, and Cass, 32.

They wanted to spend the next chapter of their lives near their business, but were hoping for a radical departure from the traditional homes they had lived in. The hilly lot they owned behind the factory was not very large, so building a house on top of the factory made sense. For inspiration, they drove along the rivers, photographing old steel structures; the one they liked most was a steel building on concrete pillars that jutted out over the Monongahela. But when they showed the photos to architects, their ideas, Ms. Zielinski says, were awful.

“One architect just made a section of our factory roof flat and put a traditional house on top of it,” she says. “One did a house where one section was glass, and we could look down into the factory. I said: ‘Why would I want to look into my shop? I just spent the whole day there.’ ”

Mr. Fisher, who had started his own firm, Fisher Architecture, a few years earlier, studied the picture, and then suggested something different: building the spine of the house on the lot behind the factory and cantilevering a section over the factory roof. At one of their first meetings, Ms. Zielinski recalls, he drew a sketch for her on a paper towel. “I was very calm, but my whole insides, there was like a party going on. I went out to the factory and said to Bob, ‘We have our architect.’ ”

Mr. Zielinski refused to give him a budget. “I just said, ‘Build it, and when we run out of money, we’ll stop and make some more,’ ” he says.