The setting is an industrial suburb in North London, a serviceable, worthy but slighty tired-looking factory, designed in the fifties by Arup Associates. The client, a manufacturer of rubber car mats, asked Robert Sakula and Cany Ash to design a staircase which would give access to the company’s first-floor offices and act as a landmark. The result is a soaring steel-and-glass structure topped by a glass canopy which seems about to take flight. Its crystalline, hard-edged complexity is a symbol of the advanced technology which takes place inside - behind the saw-tooth brick facade lies a vast hall where cadcam computers operate and control state- of-the-art milling and cutting machines, producing car mats for almost every European and Japanese model of car.
The client wanted a staircase wide enough for two people to ascend it comfortably side-by-side. It leads to a triangular top landing sheltered by the oversailing canopy and leading, through a glazed lobby, to the upper-floor offices.
The dynamism of the structure is created by the complex and opposing geometries of the canopy, the steel stair and the glass balustrade. The stair is a helix, formed by a single 219mm-diameter chs string winding round a 2m-diameter void and interrupted by two horizontal landings - a by-law requirement - which continue the helical curve on plan. The stainless- steel treads rest on tapered steel supports which cantilever from the string, welded at their ends to a smaller 40mm-diameter chs balustrade support.
The balustrade is made of triangular panels of 10mm toughened glass fixed with their apexes alternately upwards and downwards, with 30mm gaps between the side edges. They rise in a faceted sweep from the bottom of the stair to the top, forming a continuous helix without allowing for the horizontal landings. The handrail maintains a consistent height above the treads and the panels of glass are fixed to it at three points, the positions of which vary from panel to panel.
The ‘butterfly’ shape of the canopy is formed from six panels of toughened glass supported by canted steel ribs which cantilever from a steel spine of box beams. Both canopy and staircase are supported by a complex triangulated structure anchored to the heavy concrete frame of the factory itself. This consists of a new steel column braced with steel rods and a floor beam, all neatly concealed within the wall of the new lobby. One of the rods projects beyond the wall to support a raked tie which cleverly connects to the staircase landing and the top of the helical steel string, and a raked strut which supports the canopy. At the edge of the wall the canopy is bolted to a series of ties and beams which transfer the load to the new column.
The structural load paths work as follows:
the vertical forces were taken down through the new internal column
torsion forces were resolved in the connection to the face of the podium
lateral forces were triangulated in the first-floor landing slab and ultimately resolved in the connection to the podium.
At the base of the stair an area of paving is raised above the level of the car park. The lowest tread of the stair is a stainless-steel platform at the same level as the paving; it conceals and gives access to two manholes.
Sparkling by day, and floodlit at night, the stair and canopy create a landmark on the busy main Tottenham High Road.
Ash Sakula Architects: Robert Sakula, Cany Ash, Alcinoo Giandinoto,Faraz Ravi
Ing Ealtoir,David Warren
Michael Baigent, Orla Kelly
Marshall Howard,R F Peachey