Appearance, sustainability, and technology converge in the façades of The Roofs


The completion of the Grotius towers, now known as The Roofs, has given the Hague's skyline and city entrance a major boost. The most distinctive feature of the 120- and 100-metre-high residential towers is the spectacular “pixel crown”. Towards the top, a ‘crumbling’ effect is achieved, resulting in beautiful outdoor spaces with views over both the city and the sea. And the rest of the façades also have a cubist look with large windows, allowing maximum daylight to flood in.

Photo:: Egbert de Boer 

WICONA was involved in The Roofs at an early stage, working in a construction team alongside façade builder Alkondor Hengelo, building consortium J.P. van Eesteren/BESIX, architectural firm MVRDV Architects and developer Provast. It was one of two system suppliers brought in to design the window systems and fixed frames used in the project. 

Lead time of just five weeks 

WICONA excels when it comes to developing and producing project-specific solutions. “The Roofs is a real testament to this,” states Raimond Stassen, project manager at WICONA. “For example, the project includes a lot of window doors. By this we mean inward- and outward-swinging window systems that can also be used as doors. We had to figure out how to make these systems as windproof and watertight as possible. In collaboration with Alkondor Hengelo, we made several mock-ups for the window doors, windows and fixed frames. Over a lead time of just five (!) weeks, we made no fewer than ten project-specific moulds and extruded, coated and delivered the profiles. All the mock-ups were tested internally in our test laboratory for windproofness and watertightness.” 

Photo: Egbert de Boer 

Technically and aesthetically distinctive 

This project had a minimum requirement of 600 Pa in situ (on the construction site, ed.). “In our test laboratory, we achieved a final value of 900 Pa for the window doors and 750 Pa for the project-specific flat windows,” confirms Stassen. “And even on site, we met the 600 Pa requirement without any problems. This is a major achievement, which we owe in part to the large number of sealing lines in our system. We also created specific connection pieces to ensure consistent lines across the project. On the inside, the window door sits fully flush to the wall – a feature that won over the building consortium, architect and developer.” 

Sustainability first  

Another important factor was the sustainability of the profiles, stresses Stassen. “Our profiles are based on one of the most durable aluminium alloys in the world: Hydro CIRCAL. This revolutionary alloy contains 75% recycled end-of-life aluminium (post-consumer scrap) and has the lowest carbon footprint in the world: approximately 2.3 kg CO (1.5–2.3 kg CO) per kilogram of aluminium. Additionally, in the non-combustible systems, all polyamides are recycled. So the profiles tie in perfectly with Provast’s sustainability commitment." 

Successful fire tests 

The Roofs is built on a plot the size of a postage stamp. “We had to consider a lot of adjacent structures lower down,” Stassen says. “This placed special demands on the systems’ fire safety, for example. We more than met the EI30 standard required for our products, and successfully continued testing up to EW60 (!). And that was using 30-minute fire-resistant glass! It’s an extraordinary achievement that we’re very proud of."  

Photo: Egbert de Boer 

Conforming to design requirements and applicable standards 

A curtain wall was initially planned for the plinth façade/entrance area of The Roofs. However, an alternative solution with a fixed frame system was devised during the feasibility phase. “We applied for and obtained an attestation of conformity (AoC level 1) for the extremely large façade dimensions,” says Stassen. But there were still more challenges to overcome. “The design included doors that were 3 metres high, but because several of them also serve as panic doors, they could only have a maximum height of 2.50 metres, partly because of the operating force. The other components of the frame system were adapted accordingly. The construction team worked closely together to achieve a solution that came as close as possible to the architect’s design aesthetic while also complying with all relevant standards.” 

The window systems underpinning The Roofs are the WICLINE 75 evo and WICSTYLE 75 evo in their Fire Protection (FP) versions. To keep the project progressing at speed and reduce the workload on the construction site, as many frame elements as possible were delivered to the project complete and glazed. 

Client: Provast 

Architect: MVRDV Architects 

Contractor: Building consortium J.P. van Eesteren/BESIX 

WICONA partner: Alkondor Hengelo 

Location: Den Haag(NL) 

Completion: July 2022 


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