P.C. Hooftstraat 138

The P.C. Hooftstraat is one of the most elegant shopping streets of Amsterdam, located in the heart of the Museum quarter. This 19th century street, filled with traditional Amsterdam townhouses, has grown into a place where heritage and design meet each other. 

The recent, most remarkable developments in the P.C. Hooftstraat have taken place at eyelevel; with a contemporary, fresh take on the streets’ façades. The latest addition is the showstopping façade designed by UNStudio and aptly named “The Looking Glass”.

In “The Looking Glass”, three curved glass panels descend from the upper floors, resembling the flow of frisky fabrics. The panels are bonded with structural silicone to the adjacent glass panels. Slender stainless steel profiles in between the panels define the glass box shape. 

For this façade, client Warenar Real Estate brought a team together of UNStudio, ARUP and Octatube. We were invited as a Design & Build partner to do the pre-engineering, technical design, the production and the assembly. 

Pre-engineering
The goal of pre-engineering is to get an impression of the (technical) feasibility of the design. It allows us to optimize the design; resulting in better cost-efficiency and an idea of potential risks in the process. 
For this façade it comes down to meticulous detailing and a constant pursuit of quality. Together with the client, UNStudio and ARUP we organized several design workshops. This meant coming together every two weeks to collectively clarify the wish and the vision.

Curved glass
The façade consists of three glass and stainless steel boxes with curved glass and multiple glass joints. It starts flush with the adjacent buildings and cantilevers outward while moving upwards. The fact that this gradual movement takes place within one shape is remarkable. It emanates a fluidity you wouldn’t associate with glass.

The glass used in the P.C. Hooftstraat façade is produced by our partner Cricursa in Spain. The panes are annealed and laminated with a SGP interlayer. Both curved (hot-bent) as well as flat panels were used. 

Structural silicone
The boxes are entirely bonded by means of structural silicone, no bolts were used. As the glass cantilevers outward the silicone bonding has to withstand higher levels of tensile stress. By doing extensive iterative calculations the structural silicone is able to accommodate this as well as the tolerances in temperature differences and tolerances between the curved glass and stainless steel (around 2 mm in all directions).  

Stainless steel
For the stainless steel work we partnered with Dutch specialist Veratio. We delivered a 3D model that Veratio used to make a proposal for the stainless steel elements, few 2D drawings were used because of the complex geometry. 

It was a true technical challenge. As the tolerances were extremely tight and the glass had to fit perfectly, the tolerances on the stainless steel were precision work. Some stainless steel elements were cut out curved in one direction and later bent in the other direction, creating a double curved element.  

Veratio made a mould of every individual steel profile, including spacers, in which they placed the 3D shape. It was checked whether the stainless steel was made to size. Sometimes these moulds are also used to make welding assemblies. A precise job and Veratio proved to be the most knowledgeable partner and craftsman to do it. 

They developed an extensive checklist to make sure every steel element had the same finish. Quite a challenge, as everything was done by hand. It was an advantage that they had recorded everything well so that consistency could be achieved.

“We enthusiastically dove into this technical challenge. The bar was set high and top quality was pursued in all areas. The interaction between Veratio and Octatube led to a wonderful end result. We didn’t experience it as a customer-supplier relationship but really as a collaboration, which came about in a natural way.” 
Martin van Dam, Veratio

Brickwork
The glass boxes are surrounded by special brickwork. Up to the first soldier course of bricks we incorporated a stainless steel strip in the joints, that pulls the traditional architecture together with the contemporary façade. 

Horizontal to vertical
The most spectacular part of the execution of this project was the rotation of the glass boxes during the installation. They were horizontally glued in our factory and rotated on site to be vertically mounted into the facade. 

We designed a custom steel auxiliary frame that functioned as a rigid mold around the glass boxes during assembly and protected the boxes during transport and hoisting. As the glass elements are being kept together by a structural sealant, it was important not to put a heavy load on them during transport and during the rotation from horizontal to vertical. The deflections of the glass boxes and the steel auxiliary frame had to be kept to a minimum and all stages of assembly were therefore calculated. 

Because of the advanced pre-fabrication in our factory the glass boxes could be mounted within just two days. 

Structural Engineer / Project Manager
Our colleague Iris Rombouts was involved in this project as a structural engineer as well as project manager. Here at Octatube we encourage these dual positions. Currently we’re in the middle of a transition to a self-directed organization. Instead of operating top-down, we strive for a distribution of ownership over the organization. This gives employees and teams freedom and enables them to take initiative and make decisions. 

“I love combining hardcore calculating with project management. Not only is it an advantage for the client to have a partner that has technical knowledge, it’s also pleasant for yourself: you are involved in the project on a very broad level. Throughout the project, you remain informed. It feels very efficient to me and I get a lot of energy out of it!”  Iris Rombouts

A showstopper
In many ways “The Looking Glass” was a job for a Swiss watchmaker. It all came down to the exact millimeters – from the silicone bonding to the glass and steel connections as well as the steel frame and the rotation on site. 

The end result is a true showstopper that we’re extremely proud of. This remarkable façade, for client Warenar Real Estate, came together in collaboration with UNStudio, ARUP, Brouwer & Kok and Wessels Zeist.

Photography by Eva Bloem