[School design] St Silas was Capita Symonds’ first venture into Level 2 BIM. On such a complex scheme, this was no small task, writes Felix Mara. Photography by Nick Guttridge
Capita Symonds’ St Silas Church of England Primary School, which replaces a previous Victorian incarnation on a small hilltop site in northwest Blackburn, opened in April, just 22 months after initial client and user consultations. It is successful on many levels, not least for the way it enhances the dense surrounding townscape of terraces, which frame views of St Silas, and its integration with its Pennines setting.
Its simple volume belies its complex internal layout. Externally, the school is defined by a riot of locally sourced Perspex fins, which also combat solar gain and discomfort glare and conceal an inexpensive enclosure, shrewdly made weathertight at an early stage in the construction. Ingenious volumetric planning and the use of rooftops as play areas have provided a mix of flexible learning and support spaces and facilities. Access to external areas defies the limitations of a site that is much smaller than BB99 recommendations for primary schools, with 20 percent of the site transformed into community gardens.
A Church of England-run school at full capacity, with 99 percent of its pupils from an Islamic background, in a largely Indian and Pakistani neighborhood, the new St Silas was also expected to convey the aspirations of pupils, teachers and community and to be open and friendly. The project’s tight programme was driven by concerns that, following the demolition of, and decantation from, the original school, funding could be withdrawn at any point. As complex a brief as you could imagine.
St Silas is also a BIM project. You might ask why, with this level of complexity, it was chosen by Capita Symonds as its first venture into Level 2 BIM with Revit modelling by its architectural and structural engineering divisions, drawing on input from its MEP disciplines. ‘We chose St Silas because it was a tangible project and was only five minutes away from our Blackburn office, where the necessary staff were located,’ says director Chris Boyce.
Boyce has been working with Revit since 2004, although he makes no secret of the fact that he is completely dependent on his colleagues to operate the software. ‘Because it was an enormous business risk, much higher than one of our prison projects, I took personal control of the job and dictated its direction.’ As it happens, most of Capita Symonds’ hopes for the successful use of BIM in the project were fulfilled.
Like many professionals who are actively involved in BIM, Boyce insists that it is an approach to design and construction, rather than just an intelligent 3D modeling package. As it happens, Revit was also centre stage on the St Silas project, with subsidiary use of 3ds Max, Ecotect and Navisworks, all marketed by Capita Symonds’ global partner, Autodesk. The collaborative working at the core of this approach suited Capita Symonds’ multi-disciplinary role. Boyce was also excited, and influenced, by parallels between BIM and manufacturing processes.
But the most striking advantage of using BIM was its transformation of the fourth dimension; not only compressing the programme, but also freeing up its sequence. ‘BIM gives you more control and you can do a lot more earlier,’ says Boyce.’ We started accurate ceiling layouts before we went to planning.’ Although he is wary of overloading models with file-bloating, memory-guzzling and time-consuming detail and believes that conceptual design should begin with hand-sketching, Boyce stresses the benefits of being able to work in any sequence and take advantage of advanced BIM capability in early stages.
BIM was particularly useful for two purposes: first as a tool for analysis and measurement, and second as a means to explain and visualise the design of St Silas. Using BIM as an analytical tool, the architectural team quickly modelled St Silas’s complex volumes and spaces from hand sketches to accurately test ideas proposed to the client and users. Accurate data for the thicknesses of partitions and retaining walls enabled the layout to be fine-tuned early, helping the designers to optimise efficiency by minimising superfluous circulation space.
After proposing a new location for the school on the north side of the site, where it wouldn’t cast shadows on the playground, Capita Symonds used Ecotect to analyse the impact on neighbouring residences and quickly gauge the town planners’ reactions, which were positive. Calculating the weight of steelwork and the size and mass of foundations helped the design team to monitor costs. Wind-load modelling enabled it to challenge the engineering proposals of the sub-contractor for the Perspex fins, which were a particularly sensitive design feature.
Capita Symonds quickly added details of materials, finishes and construction to the Revit model, which could be used to explain the design features to the client, users and planners, avoiding surprises and confrontation at a later stage and it was soon possible to demonstrate the finer spatial qualities of the school and assess its qualitative lighting design.
Unlike BFLS at the Royal Welsh College of Music and Drama (AJ 24.05.12), Capita Symonds was very much the initiator of the BIM process at St Silas, having ownership of the model until it was acquired by Balfour Beatty when Capita Symonds was novated and continuing to work with it afterwards. Although the model was used for supply chain testing, the subcontractor’s involvement with the BIM process was limited. Likewise, the potential to integrate the specification with the model was not fulfilled, although this will be a priority for Boyce on future projects.
He is in no doubt that BIM enabled Capita Symonds to make savings on staff time and other resources and hesitates to dismiss arguments that clients might be justified in paying lower fees for a BIM project. Taking a positive view, he emphasises BIM’s potential to free up time, which can then be used to improve design quality.
AJ Buildings Library
See images, drawings and data of Capita Symonds’ St Silas Primary
New tricks: Capita Symonds' St Silas Primary