Shane Kelly, research and development manager at Longcross, on the Castle Mill graduate student accommodation, University of Oxford.
Castle Mill is a 312-bed student accommodation development, split across eight main blocks and three gatehouses, which vary in height from four to five storeys.
The main blocks were originally designed as concrete-framed structures built using insulated concrete forms (ICF) and piled foundations. Work had started on site, but 12 weeks in, technical support and cost issues related to the ICF system and logistical problems caused by the fact that the numerous concrete deliveries had to come in via a narrow lane, meant we had to urgently rework the design for the whole development.
Fusion Build is a pre-insulated light-gauge steel external wall system developed for low- and medium-rise buildings. Although similar in capital cost to concrete, the lightweight nature of the system enabled us to do away with the scheme’s 500 piled foundations and related groundworks and reduce the depth of floor slabs from 700mm to just 250mm.
The factory pre-insulation process involves filling the voids in the frame with thousands of poppy seed-sized insulation balls, which when exposed to steam expand to fill the structure making the finished panels around 98% air. In conjunction with an additional 62mm of external insulation, also applied in the factory, the panels give an impressive U-value of 0.21W/m2K.
Our client, the University of Oxford, wanted the buildings to stand the test of time and was nervous about using a lightweight steel system. Acoustic performance was also a major concern as the site is next to the main railway line, so we built mock-ups of every wall and window, internal wall and flooring scenario to test noise transmission and all passed the required decibel restrictions. Prefabrication also guaranteed our quality of build, enabling tolerances of about +/-5mm and minimising waste on site.
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