Constructing a precast load-bearing facade
The cladding concept of Sergison Bates’ and Jean-Paul Jaccaud’s Geneva housing and creche building
Rue du Cendrier social housing and creche
Sergison Bates and Jean-Paul Jaccaud Architectes
The tectonic concept for constructing the precast load-bearing facade at Rue du Cendrier is that of a column-and-beam structure expressed as heavy, tall elements at street level, gradually becoming finer and more repetitive on the upper residential floors. The plinth of the building is designed as a double-height arcade at ground level, with a mezzanine above with recessed loggias that act as external spaces for the creche.
Structurally, it serves as a rigid box that allows the offsetting of the structural grid of the load-bearing facade above. The upper five floors describe a freer outline with subtle folds in the long south-facing and east elevations and chamfered corners at both ends of the facade.
Proportions were judged using large scale models, adjusting column and beam dimensions as well as their thickness (460x300 column and 700x300 beam on third and fourth floor, 350x235 column and 580x235 beam on fifth to seventh floor).
Source: Joel Tettamanti
On site, each element was fixed to a concrete upstand of the element below and temporarily propped to be held in place when the concrete slab above was cast against the beam’s reinforcement to form a structurally stiff joint between horizontal and vertical building components.
All elements are cast to a 5mm accuracy and interlock seamlessly to guarantee waterproofing and a continuous insulation layer.
Vertical joints are visible above the centre of columns and horizontal joints between sill and columns. The average U-value of the facade, in combination with a mechanical ventilation system cast into the floor slabs, meets the requirements of the Swiss Minergie code.
On the upper floors columns and beams were combined into larger forms that can be described as Ms and Ts, allowing for greater efficiency in the manufacturing of the elements and swift assembly on site.
While on the lower three floors precast elements were made from solid concrete, the upper five floors are designed as sandwich panels which consist of an inner structural layer (200mm), insulation (min 180mm EPS with polyurethane lining) and an outer U-shaped cladding shell (80mm) which wraps around the insulation to create the window reveals and is fixed to the internal structural concrete using stainless-steel anchors.
This variation reflects the change in the position of the thermal envelope in relation to the structural plane of the facade. A further variation in the system of precast facade elements takes place in the ground floor columns on the west facade. These have to withstand greater horizontal forces and are therefore built as in-situ columns lined with precast concrete panelling.
Small adjustments to the primary geometry were introduced to allow the integration of secondary components such as textile blinds and balustrades, while an offset in the inner and outer shell accommodates the windows. The rough concrete inner leaf is lined by a low wooden sill and architrave.
Sampling the concrete colour
Inspired by the colour of the neighbouring natural stone facades, the concrete mix was chosen and adjusted to range between green and warm greys. Testing material samples on site, three different recipes were selected that use a combination of limestone sediment from the Rhône and Ain rivers as aggregate (grey or beige-brown), grey or grey and white cement and ochre iron oxide pigments.
The three resulting tones were applied to the different facade elements, which were then arranged compositionally to achieve subtle nuances and visual depth.
Architects Sergison Bates with Jean-Paul Jaccaud Architectes, Clients Housing: Fondation Ville de Genève pour le Logement Social (FVGLS), Crèche: Service d’Architecture ville de Genève, M&E engineer Raymond E Moser, Structural engineer Sancha, Electrical engineering MAB Ingénierie, Public Health engineering Schumacher Ingénierie, Facade elements Prelco