Winner: Arnold Laver Gold Award and Structural Award
This is a valuable addition to the impressive list of Maggie’s centres, which use carefully considered architecture to create a place of refuge where people affected by cancer can find emotional and practical support. The Manchester centre establishes a domestic atmosphere in a garden setting, while accommodating a range of flexible spaces from intimate private niches to a library, exercise rooms and places where people can gather and share a cup of tea.
Naturally illuminated by triangular roof lights, the building is supported by lightweight timber lattice beams. These beams act as natural partitions between different internal areas, visually dissolving the architecture into the surrounding gardens. Their structural ingenuity, which is described below, gives them a visual lightness and an actual transparency in the lattice areas which is appropriate to the setting.
Timber was chosen as the primary building material for its aesthetic and structural properties, as well as for cost and carbon efficiency. The desire to create a homely environment, far from institutional, clinical spaces, defined the approach to the building’s environmental design. Natural ventilation, daylighting and radiant floors provide a comfortable environment in a low-energy building. Passive design elements such as the deep roof overhang help to shade the building from excessive solar gain during the summer, and capture the low winter sun – minimising energy consumption.
The sustainability of the building in-use has also been considered with the use of water-efficient fixtures, waste separation and a greenhouse.
The judges were very impressed by many aspects of the building, and enjoyed the creative tension by which an architect known for rigour and elegance had achieved a gentler aesthetic that was appropriate to this use without sacrificing any signature strengths.
In particular, they felt it deserved the Structural Award because of the originality of its design. They said: ‘It is a project that all engineers would love to work on. It demonstrates that a simple, coherent structural diagram, when beautifully and carefully developed and detailed, can result in a solution of considerable merit. The engineer has undertaken a rigorous analysis to reduce material to the minimum that is necessary, but has additionally engaged with leaders in the supply chain to explore cutting-edge fabrication possibilities. The result is an ingenious and original structural system of opposing CNC-cut "ladder beams" which are laminated together to create the trussed members. The moment connections required to develop the portal action have been detailed as elegant nodes, with only a concealed steel strap over the top to strengthen the timber jointing arrangement.'
Architect/structural engineer Foster + Partners
Main contractor/builder Sir Robert McAlpine
Specialist contractor Blumer Lehmann AG /SJB Engineers
Landscape consultant Dan Pearson Studio
Wood supplier Metsä Wood
Wood species Nordic Spruce
Technical study: Maggie’s at the Robert Parfett Building
In common with all Foster buildings, the design of Maggie’s is a synthesis of the brief, structure and choice of materials. This is clear from Norman Foster’s earliest sketches, a delicate filigree of timber elements which resemble the extended skeleton of a bird, its wings outstretched at the sides. Within this sketch are contained all the elements of the plan – low in scale to respond to the suburban context, long on the east and west elevations to link to the surrounding garden landscape, and with a central spine which encloses space for administration and services. The spine rises at its centre to create a continuous glazed rooflight which floods the rooms below with natural light and allows just enough headroom for a mezzanine floor. The nature of the building suggested that the material for the structure would be domestic in scale, and would emanate warmth yet be sustainable; timber was the inevitable choice.
The structure is exposed throughout the building and consists of laminated veneer lumber (LVL) trusses each with a set of diagonally opposed double web elements, creating a delicate filigree of timber. A series of LVL trusses forms the central spine; they are set on the diagonal and rise to the ridge, where the spaces between them are infilled with triangular glazed rooflights. At their bases each pair of diagonal trusses meets at a triangular LVL node; this connects them to the LVL column below and joins both to an LVL truss beam which cantilevers outwards to support the gently sloping roof, supported at its end by a slender steel column.
All the trusses taper to reflect the magnitude and orientation of the forces acting on them – any portion that is superfluous has been removed. Analysis of the stresses caused by wind load (sideways) and snow and dead load (vertically) indicated where the timber could be optimised. The 7.5m-long cantilever roof trusses taper as the bending forces reduce towards to the cantilever tip, through the column to the pin connection at the ground, and at the central node above the spine. On the top and bottom flanges the ends become solid as the shear force increases along the section. A key component of the structure is the node, the point where vertical loads from the roof are transferred to the 3.1m-high columns below. The node also acts as a portal frame haunch to provide the rigidity required to resist horizontal wind forces which act across the structure
LVL creates a sophisticated piece of engineering, strong and lightweight, yet with all the warm tones and domestic qualities of timber. Trusses were produced from Kerto LVL provided by Metsä Wood; 3mm thick rotary-cut sustainable Nordic spruce veneers were bonded to form a continuous board and cut to suit the required basic shape. These were transported to the factory of timber specialist Blumer-Lehmann in Switzerland where they were CNC-cut to form the series of tapered layers which make up each truss. ‘By studying the process we were able to maximise opportunities to refine it,’ explains project architect Darron Haylock. For instance, although all the LVL layers which make up a single tapered truss follow a consistent perimeter profile, two inner layers were specially cut to create the two sets of diagonal web flanges; all layers were then dowelled and glued together to form the final truss. Likewise, the LVL layers of the truss columns and cantilevered beams were extended at the ends to create the triangular node; during construction the column layer of the node slotted between the cantilever truss layers of the node in a manner similar to a halved timber joint.
All fixings between the trusses are concealed; a metal Y-shaped strap along the top of each cantilever truss connects it to the diagonal roof trusses.
Waste generated during fabrication of the trusses was used as fuel to heat the Blumer-Lehmann factory. The process offered all the advantages of timber prefabrication: fast and efficient construction, elimination of wet trades and a superior pre-finished product.
This is an abbreviated version of one of more than 80 case studies on TRADA’s website. To read this and others in full go to trada.co.uk > Wood information > Case studies