We questioned Sofie Nijs, interior design specialist at MAMU Architects, about the key points of the design for the staircase at the Carglass office at Hasselt, Belgium.

What was the primary aim of the design?
It was really important for the client to have a staircase that was a genuine eye-catcher. So, from the beginning of the design process, the idea was to create a staircase that appeared to float, but had no obvious structural support. And this meant that our engineer was closely involved at an early stage, to ensure absolute structural integrity.

And how was that structural integrity achieved?
Essentially, the stair treads and balustrade rotate around a single steel column, which holds the whole structure up. The stairs are supported by three secondary steel ‘trees’ whose oblique steel elements spring outward from the column.

A completely black staircase is unusual. Why black?
Well, for obvious reasons I wanted to highlight the use of glass and maximise reflectivity as a strong contrast to the reception area, which is basically white-walled, with plenty of natural light. So, the balustrade is composed of black glass rising from a U-profiled indentation in the top edge of the black steel cheeks at the base. The reception area has overhead fluorescent light strips, which I realised would be reflected at unusual angles on the black glass – so, you could say that the geometry of the stairs is decorated with geometric strokes of light. 

Was the balustrade easy to achieve?
It was easy to design and draw! But it was Ee who had to perfect it, and make absolutely sure that the joint-lines between the glass and the steel were precise – because this accentuates the geometric precision of the staircase. This was quite challenging but, as you can see, Ee achieved it. They also matched the black of the glass and the black of the steel very accurately – definitely not easy! – and this increases the monumental character of the staircase.

Speaking of monumental, does this mean the stairs were constructed in one piece?
Yes, which meant that great care had to be taken with the transportation of the staircase from Ee’s factory to the Carglass office. And, once it was in position in the reception area the final adjustments to the weld-seams had to be made to lock the structure together in situ.

And was that the final fine-tuning of the staircase?
Not quite. The Carglass reception area is a mostly open two-level volume, so the sound made by shoes on the steel treads had to be minimized. Fortunately, this was quite easy – Ee applied a layer of PU to the treads to deaden reverberation.