Powerhouse Company

An Evocative Expansion

We converted a neglected 1968 office building into stylish apartments – creating our own dream home in the process by adding a glass-box penthouse to the roof, framing the superb views of Rotterdam’s skyline. While it’s a real feat of contemporary engineering – as the largest load-bearing glass façade in north-western Europe – our glass intervention was inspired by America’s Midcentury Modern architecture: a transatlantic complement to the European Modernist structure it stands on.

When Powerhouse Company first moved into rented office space at 399 Westzeedijk as part of a live-in guardian scheme, the building was neglected and unloved. But the 1968 design by J. W. C. Boks clearly had huge potential, and Powerhouse Company founder Nanne de Ru and his wife Nolly Vos set their hearts on transforming it – with an eye to living at the top of the building, with its wonderful views of the Rotterdam skyline.

Eventually, the couple was able to buy the building and convert it into apartments together with developer Being Development. The result is West 399, a sleek residential building with a floor for offices and a spectacular penthouse – the dream home of De Ru, Vos and their three children.

‘We didn’t want to lose this place. Taking the initiative for re-use was the only way to live at the top of the building.’

– Nanne de Ru

Although West 399 started life as a high-quality Modernist building, it was much altered in the 1980s and 1990s. The renovation began with stripping away these additions to reveal the original beauty of the interior, complete with lofty high ceilings, round columns, and mahogany-framed strip windows. The exceptionally rich palette of materials was restored to its former glory: warm brickwork outside, with slate, travertine, and solid hardwood inside.

Rich materials and high-quality detailing similarly define the glass-box penthouse structure on the roof, a new addition that develops the European Modernist idiom of the building with a thoughtful contemporary interpretation of its transatlantic incarnation. Originally planned as a two-floor construction, De Ru and Vos changed their design when one of the apartments below failed to sell. The 450m2 penthouse apartment now comprises a one-layer new-build perching on the roof and surrounded by a roof garden, and a portion of the existing building below that roots it in the original structure.

‘Materials are important to the mix, as we wanted to incorporate ones used in post-war Rotterdam, such as travertine, mahogany, and green stone.’

– Nolly Vos

The two floors are linked by a generous, champagne-colored spiral staircase, via which visitors arrive in the living room, surrounded by glass and by jaw-dropping views of the river Maas and the city skyline. The penthouse façade is the largest load-bearing glass façade in north-west Europe. The roof rests on top of it, anchored by steel cables concealed in the joints between the glass sections. The glass is set at a slanting, rather than straight, angle for added strength. Outside the glass rectangle, a generous overhang provides shade and repeats the form of the patio below. Grey was chosen for these surfaces to avoid glare.

Behind the glass rectangle, a more closed volume presents a travertine façade to the outside world, while inside the spaces offer greater privacy and intimacy. The music room is lined in American walnut and features a large circular window with views over the harbor. The kitchen diner is executed in a sumptuous palette of mahogany wood, red travertine, matt gold resin and green serpentine stone. The master bedroom is crisply white, with the bathroom entirely covered in travertine. On the level below, in the original building, the three children’s rooms are treated as autonomous furniture objects in space and clad in American walnut. Organic materials like wood, stone, and leather plus slices of color – the pink glass wall next to the spiral staircase and the gold cabinets in the kitchen – add warmth to the interior. As a finishing touch, art is carefully curated throughout to create an integrated experience of space.

‘Behind the travertine façade, the inside spaces offer warmth, greater privacy and intimacy.’

– Anne-Ragnhild Larsen