PROJECTS
A series of LVL trusses form the central spine; they are set on the diagonal and rise to the ridge.
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) indicate where the timber could be optimised. The 7.5m long cantilever roof trusses taper as the bending forces reduce towards the cantilever tip, through the column to the pin connection at the ground, and at the central node above the spine. The ends of the top and bottom flanges become solid as the shear force increases along the section. The node is a key component of the structure, 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 the horizontal wind forces which act across the structure.
The use of LVL creates a sophisticated piece of engineering, strong and lightweight, yet with all the warm tones and domestic qualities that timber provides. The trusses were produced from Kerto LVL provided by Metsä Wood; 3mm thick, rotary-cut sustainable Nordic spruce veneers 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,” explains Darron Haylock, project architect.“ We were able to maximise opportunities to refine it.”
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 the layers were then dowelled and glued together to form the final truss. Likewise, the LVL layers of the truss columns and the cantilevered beams were extended at the ends to create the triangular node; during construction the column layer of the node slots 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.
SUSTAINABILITY
The desire to create a homely environment, in contrast to the institutional space of a clinic, defined the approach to the building environmental design; natural ventilation, daylight and radiant floors provide a comfortable environment within 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 – therefore minimising energy consumption. The sustainability of the building in use was also considered, with water efficient fixtures, waste separation and a greenhouse.
// FEB / MARCH 2017 37