Jo Vanweert knew two things when he decided to build his first home: It would be on the highest point in his small home-town of Bilzen, Belgium, where his family has lived for generations, and it would be designed by his cousin Jan Vanweert, an architect 11 years his senior. Jo told his cousin he wanted a house that had clean lines inspired by classic modernism and that took advantage of its hilltop site. What his cousin delivered has a modernist rigor tempered with a surprising softness, a twist that turned out to be perfect for the younger Vanweert’s evolving family.

The architect and his team designed a glass box sandwiched between two concrete slabs as the top floor—the plan directly references Mies van der Rohe’s Fifty by Fifty Feet House—and placed three bedrooms, one bathroom, and the entrance on a lower floor dug into a knoll.

The rooms down below all have sunken patios that allow for natural light and private outdoor spaces. (A psychiatric nurse, Jo finds the subterranean bedrooms perfect for sleeping after a night shift.) A single pillar on each of the house’s four sides stabilizes the structure and allows for a gap between the top of the patio walls and the upstairs floor, creating the illusion of a glass pavilion floating above the ground.

The space upstairs is divided into four quadrants—kitchen, dining area, living room, and playroom—by arcs of concrete that Vanweert calls “curtains.” “Only parts of the walls support the structure, so we could cut away the extra concrete to make these soft, curved shapes,” he says.

The effect is twofold: The rooms are separate yet connected by partially open sight lines, and the curves of the cutaways soften the interior and make the boxy shape feel more inviting. Sliding glass doors open to a narrow balcony around the full perimeter of the concrete floor slab, although it could more accurately be called a ledge, given the lack of railings to prevent the occupants from falling onto the patios below. The views stretch all the way to Maastricht, just across the border in the Netherlands.

Jo initially envisioned the home for himself and his now 13-year-old son. But during construction, he met his future wife, Sofie Hens, and before the house was completed, the two had a daughter, now a year old. Despite the growing family, little changed about the original design (though railings are now under consideration), but what appears to be an unforgiving shape has been able to adapt to family life.

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The older ones say they don’t mind sharing a single small bathroom, while the baby enjoys the most spacious quarters of all, with a big playroom upstairs and the largest of the bedrooms below. The concrete curtains further contribute to the human scale of the home by allowing people to move about through the cutouts. “We actually use those more than the wider spaces along the glass walls,” says Jo. “It has really surprised us.”

Project Credits:

Architecture: Dhoore Vanweert Architecten

General Contracting: Clauwers

Structural Engineering: Yuvico