"I’ve never understood the distinction between domestic and commercial architecture,” says South African architect Gregory Katz. “A lot of what I do is an attempt to use engineering materials in a domestic setting in a new, clever way.” One of essentially three identical concrete boxes, the Norwood home Gregory moved into months before marrying his actress wife, Caryn, cuts an incongruous but captivating sight in this leafy middle-class suburb of Johannesburg. The trio of houses contrasts with the area’s mishmash of architectural styles, where a glut of security complexes are characterized by cookie-cutter design and little space in between.

The three 3,660-square-foot dwellings at Lot 424 share over a third of an acre and answer a common desire for space, security, shared maintenance, and even a sense of community. Achieving this in an economical fashion wasn’t easy, but for Gregory, who thrives on the research and development side of a design project, it was all part of the process.

“I love the solidity, strength, and neutrality of off-shutter concrete,” says Gregory. “You can build pretty quickly with it, and the absence of fittings and finishes made the economics convincing. It wouldn’t be cost-effective for one house but it is for three,” he explains. Taking just 18 months to build, the units are designed with a shared-access service road that runs down the back of the buildings and, at 20 feet wide, is big enough to drive cars down and provide off-street parking for visitors. “Each unit is designed so that the more open side of the house looks onto the private sides of the neighboring houses,” explains Gregory. The slope of the ground facilitates this too, with each unit stepping down a bit so that none of the windows correlate.

Gregory’s ability to exploit concrete’s strength is visible in his own home, a huge expanse that feels light and spacious thanks to the absence of a single load-bearing wall. A large aperture of stack-able glazed doors softens the divide between indoors and outdoors, and the freestanding staircase and cantilevered bedroom keep the path of light and space dynamic. Upstairs, the openness continues in the main bedroom, spare bedroom, and home office where Gregory bases his practice. The modular design allows the other two units to utilize the office space for a third bedroom and study. “I’m all for modular design; it’s easy to manipulate and control, and the spin is that it allows tremendous flexibility. So the house is designed to accommodate the demands of a nursery, restaurant, or office in the future. I believe that if you put all this energy into a building, it has to be around for a long time.”

But it took a while for the developer to get the concept. “It’s an incredibly simple box, and so initially, it was difficult to convince the developer that we could surpass these connotations and make concrete ‘warm and homey,’” Gregory says. “I appreciate the super-slick minimalist look, but it’s hard to get right in this country, and I don’t see the point in doing something if you can’t do it properly.”

Studying architecture at Columbia University in New York and working for Daniel Libeskind in Los Angeles has given Gregory some perspective on this. “[Libeskind] taught me the value of experimentation. Where architecture is most often concerned with moral decisions, Daniel is unable to be anything but playful and courageous.” Another influence is maverick architect Zvi Hecker, with whom Gregory worked during a gap year in Tel Aviv and Berlin. “His experimentalism with materials and his insistence on not settling for what’s available, but rather reinterpreting it, has set me in good stead coming back to South Africa.”

For Gregory, Johannesburg is a great place to be an architect. Its origins as a swashbuckling gold-mining city where fortunes were quickly made and lost resonates even now, most notably in its architectural landscape where developers are all-powerful, and buildings go up and come down with little regard for longevity or the preservation of architectural value. “It’s an exciting place to be as there’s much to be done, but it’s not for the fainthearted,” says Gregory, who started his own architectural practice four years ago—three years after returning to South Africa.

“You have to work within what is achievable in this country. I tend to work closely with the builders, which eases the process. In fact, with this house, the builder ate most of the cost of the experimentation on the staircase, as he was just as passionate about getting it right.” After three attempts, strength-tested in situ each time, Gregory is particularly pleased with the high-tech result, achieved using a composite system of welded steel L-profiles, expanded mesh, and polymer fibers in the concrete.

It was a similar journey with the concrete finishes, starting with the boundary wall, for which they used heavy-grain timber as shutters so that the resulting molded concrete retains the impression of the timber grain. They also used laser-cut Perspex to imprint text on walls, inspired by an old technique that Le Corbusier used in the 1930s. “There’s an alchemy to concrete that allows it to take on many guises at very little cost,” says Gregory. The concrete staircase is pigmented black, a durable choice for a high-traffic area that can withstand nicks and scratches, and the slab on the terrace has been ground to expose the black flecks of Johannesburg granite used as an aggregate. Concrete countertops in the kitchen have been finished simply with an invisible sealant while the windowsills in the bedrooms form deep slabs to resemble floating shelves.

The house has also been designed to be thermally efficient with the overhang on the terrace carefully calibrated to avoid the summer sun but capitalize on it in winter, when the sun is lower and the light comes through the huge glass doors in the living area. “Our Highveld winters are good because they’re sunny, so the concrete absorbs heat during the day and gives it off at night,” notes Gregory. The radiant heating is also embedded directly into the slab of concrete. In summer the big openings and cross ventilation ensure a thorough flow of air throughout the house.

A self-confessed minimalist, Gregory is the first to admit that the architecture can’t stand alone, and that the stereotypically masculine order of the house needs a feminine counterpoint. “There’s a lot of clutter around with Caryn,” he quips. “But I love it. This place needs to be lived in and she makes it happen. The color is all her,” he says, pointing to the bright yellow kitchen cabinets. “Gregory enjoys the calculus whereas I’m more spontaneous and don’t mind living with the consequences of imperfection,” says Caryn. “But I trust him. I initially chose a paint swatch called Canary Yellow, which admittedly I loved because of the name. Gregory then agonized over the final color choice, but eventually he settled on this citrus hue and of course it’s perfect.”

They both marvel at how grown-up the house feels in comparison to their previous Art Deco apartment. “At first I thought I was moving into a mission statement for Gregory’s head, which was a little intimidating,” Caryn muses. “It’s taken a while to get used to it, but I’m surprised at how quickly I’ve managed to make the space my own. What I hadn’t anticipated was how the house makes all my little personal details like photos and tablecloths look quite spectacular. In our previous space they just blended in, but here they stand out. I really like that.” And when you consider the marital harmony this must afford, it’s the design’s most impressive accomplishment to date.