Coin Street Neighbourhood Centre, London

The use of concrete at Coin Street Neighbourhood Centre was fundamental to the low energy strategy for the building, combining natural ventilation and high thermal mass.

The cast in situ concrete rib slabs create sculptural concrete soffits; concrete walls, stairs and columns express the grain of the plywood formliner that they were cast against. The concrete structure provides a robust and material efficient backdrop for the activities of the community.

Haworth Tompkins won a competition in 1999 to design a new urban block on the South Bank just behind the National Theatre. The first phase completed in 2004, created a new housing development that occupies three sides of the block with a garden at its centre. This first phase, provides 59 dwellings, including 32 family houses and a mix of smaller flats and maisonettes.

The Coin Street Neighbourhood Centre is the second phase of the development and occupies part of the south side of the block. The Centre is a lively mixed-use community facility that provides a crèche, health facility, adult training, social enterprise support spaces, offices and conference and social spaces.

Early discussions between the architect and the client defined the need for a high quality, accessible, flexible and sustainable new building that can adapt to the changing demands of the community it supports.

This underpins the design – a robust and adaptable shell that can accommodate the current range of uses and anticipates future changes in layout and function in response to changing social demands. A cast in situ concrete frame was selected and 11m spans achieved using a ribbed slab structural solution that also reduced the number of columns and provides large, potentially multi-functional spaces.

The concrete rib slab structure is expressed in most rooms as an exposed soffit. The soffits were constructed as bespoke forms out of birch-faced plywood assembled on site. The concrete mix used included 50% GGBS (ground granulated blast-furnace slag), a recovered material from the iron and steel industry, that provides a low carbon concrete and makes the concrete paler in colour.

The staircase and walls were cast against a different grade of plywood, which has also been used as a final finish to line the lift lobby areas. The same elliptical shaped repairs to the ply-facing can be seen cast into the face of the concrete in this area. The stairs themselves were also cast in situ. Balustrades were cast afterwards. Hand trowelling was used on the stair treads and on the horizontal tops of the balustrade. The day work joint between stair-flights and the balustrade is visible on the vertical faces of the inner stairwell.

The high thermal mass of the exposed concrete structure, combined with the ventilation strategy and intelligent controls deliver a low operational energy solution. A series of rectangular solar chimneys are arranged behind the colourful glass façade along Stamford Street, establishing a second layer within the building and providing  natural ventilation, without the need for opening windows to the south of the building which faces the noisy street.

By warming the air within the south-facing solar chimneys, the sun creates a stack effect that drives the natural ventilation system by pulling air through the internal spaces from the cooler north side of the building. In the summer, night-time ventilation cools the exposed concrete structure which then helps cool the space during the day using the ‘thermal flywheel’ effect.

More information Project Profile: Coin Street Neighbourhood Centre.