WHEN Bob Zielinski, a former marine who owns a glass manufacturing company here, and his wife, Kim, showed contractors plans for the house they wanted to build — a 53-foot-long glass-and-steel wedge cantilevered over their factory — the contractors said they couldn’t do it. You’d have to get guys who build bridges and do highway work to create the support system for something like that, they said.

So, that’s exactly what the Zielinskis did.

It took three years to build, but the Emerald Art Glass House (named after the Zielinskis’ company, Emerald Art Glass) now hovers above the factory in the South Side neighborhood, overlooking the Monongahela River, railway line and bridges.

Eric Fisher, the couple’s architect, says proudly that the cantilevered extension is three times the length of the one at Frank Lloyd Wright’s Fallingwater. And that it recalls the tradition of the owner living over the shop.

The Zielinskis offer other reasons for the design. They raised two children in a traditional home in the suburbs and wanted something different. They wanted to be near their business. They also thought some privacy would be nice.

“I don’t want to be right on top of my neighbors, I don’t want to hear them fighting, I want a little peace and quiet,” says Mr. Zielinski, who has the I-know-what-I-want-and-damned-if-I’m-going-to-settle attitude of a self-made man. “I start looking around South Side to build a house, I can’t find anything I like. You’re paying $200,000 or $300,000 to be packed right into the neighborhood.”

Come at the house straight on, driving across the river up to the door of the factory on Josephine Street, and you might not notice it, for the factory is two stories high and the house is set so far back. But walk a half-block down the street, past the neighboring wood-frame houses, and look up, and it will stop you in your tracks.

The house looms over the street like a big industrial arm. There is no way it should fit in, and yet it does. For this is not just Steeltown, it’s the City of Bridges — 446, by one count. But try to find the door, and you face an obstacle: there isn’t one, at least not one you can easily get to. The driveway is hidden behind a tall wooden fence and gate.

“I like that people don’t know how to get in,” Mr. Zielinski says, opening the gate and driving a reporter in with his Jeep.

Mr. Zielinski, who is 53, grew up in Pittsburgh, the oldest of six children. He joined the Marines at 17 and then tried various jobs, from carpenter to cheese factory worker. Nothing interested him until he began dating a woman who did stained-glass repair. Mr. Zielinski asked her to teach him, and from that point on, “I was, like, addicted,” he said.

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.

Fortunately, they never had to do that. Acting as the contractor, Mr. Zielinski brought costs down to about $225 a square foot. Construction challenges included digging two seven-foot-wide holes 35 feet into bedrock and filling them with concrete and steel to support the cantilevered sections of the five-level, 6,900-square-foot house.

The entry is a high-ceilinged garage with a playful 1950s-style air-raid shelter sign in front of a commercial elevator. On the second floor is a TV room and a gym. The third floor is a cantilevered great room with an open kitchen and, a few steps up, a living and dining room offering a panoramic view. A second set of stairs leads up to the couple’s bedroom.

Ask them about favorite moments in the house, and the answer varies. Mr. Zielinski loves to sit at the far end of the living room at night, where he can see out while ironwork prevents neighbors from seeing in. Ms. Zielinski likes to watch the shadows on the glass wall in the bedroom.

“Something’s always moving,” she says. “You see things that you really didn’t notice before, that you didn’t really pay attention to, even the way the clouds come in.” It “almost feels like it breathes,” she adds. “It’s wonderful.”