Structural facade enables plinth House on South

Transparency in steel

At Laan op Zuid in Rotterdam, 2025, Huis op Zuid was completed: a multifunctional building with sports facilities, swimming pools and 104 rental apartments. Koen van Velsen architects designed the complex as a clear urban volume with a strikingly transparent plinth. This open design determines its appearance: sports and exercise are visible from the street, making the building emphatically oriented to the neighborhood and public space.

This transparency was not an obvious starting point, as the lowest building layer also forms a technical transition between different functions. Sport, public use and housing come together in the building, with corresponding requirements for safety and acoustics. It was precisely in this area of tension that the choice for steel and for a specific manner of façade construction arose.

Design choice: structural instead of clamp and cover frame

Rob Neeleman, Sales NL and Technical & Commercial Advisor at Jansen, links the mate-

rial choice to both construction and detailing. “Koen van Velsen likes to work with steel. With high facades and large windows, you need material that is strong and remains stable. Steel offers more possibilities in this regard than wood or aluminum.”

“Views right through the building, sightlines and the abundance of daylight result in a pleasant building where everyone is welcome and can feel safe,” says Koen van Velsen. The transparent facades make sports functions visible and give the building a distinctly public appearance.

Fire resistance and span as determining factors

That transparency simultaneously placed high demands on performance, including fire resistance and acoustics. In a facade with large areas of glass, this requires precise engineering, especially when the facade also performs structural functions.

That, according to Jansen, is where an important differentiating point lies. Neeleman: “The structural and fire-resistant facade is increasingly being chosen. In case of fire, bending and deformation occurs, you have to take this into account beforehand in the detailing.” Jansen therefore works, among other things, with stainless steel anchors and an anchorage that is incorporated into the cavity of the window, so that high loads can be transferred without disturbing the facade appearance.

For Huis op Zuid, a profile was sought that could achieve large spans in one go and was suitable for large windows weighing approximately 360 kilograms. The profiles used had a length of 7.82 meters and matched a standard length of 8 meters, leaving little residual material. In particular, Jansen supplied the steel profiles for the lower storey; aluminum façade systems were used in the residential floors above.

Execution and detailing

Production and assembly of the steel fleece facades and window frames was performed by Jonkers Bouwmetaal. Maarten Jonkers, director of steel window frames, points out the detailing. “The facade has no deck or clamp frame. So everything had to be thought out so that it blends in well at once. In the pool section, we also integrated sun blinds into the facade.”

According to Jonkers, the spans in particular required customization, including in the brackets and anchor points toward the main concrete load-bearing structure. It is precisely this combination of engineering, production and assembly that makes it possible to implement complex details consistently, without making concessions to the facade appearance.

In addition to the facades, the company also realized steel fencing and interior stairs. Round windows also appear in the project, for which rolled sheet material was used. “This project was packed with challenges, which we are able to meet because of the different disciplines we have in house,” said Dr. K. K., who is a member of the company's team.”

In addition to the facades, Jansen also supplied fire-resistant interior doors and special door details. Some doors are structurally glazed and flush incorporated into the façade surface. “In doing so, the glass is glued to the profile so that the whole thing lies flush,” says Neeleman. That detailing is consistent with the architectural ambition to read the facade as one continuous plane, without staggered or emphatic cover strips.