21 October 2020
Member Case Study: Stroud Chapel
The Christian Community is a movement founded in the 1920s by a group of theologians and ministers to promote religious renewal, primarily through regular communion services called The Act of Consecration of Man, and was inspired by the work of the Austrian philosopher, scientist and artist Rudolf Steiner (1861–1925). During his lifetime, Steiner was directly involved in the design of over twenty buildings in Dornach, Switzerland, in the period 1913–1925 – including the Goetheanum – which is a Swiss National Monument and one of the world’s first example of the use of sculptural concrete.
In the 21st century, it is not generally economically viable to reproduce hand crafted buildings like the great cathedrals of Europe or even the Goetheanum, so we work with a largely technology-driven industry while attempting to give the same inner experience these buildings still allow us.
The Christian Community's new chapel in Stroud is the latest in a series of three chapels designed by Nicolas Pople Architects (NPA) with Peter and David of Corbett and Tasker Engineers, being preceeded by Canterbury Chapel in 2011 and Temple Lodge in 2012. The three chapels explore the use of contemporary timber panel systems to realise complex forms and sacred geometry. For all three chapels, our brief at its most fundamental was to produce an architecture that did not have historical or cultural associations.
The existing building on Cainscross Road in Stroud was constructed in 1968 but by the end of the 20th century was already too small for its growing congregation. NPA were instructed in 2012 to begin designs for its replacement and eventually opted for a conservation approach whereby one wing was demolished to make space for a new chapel, while the original sacramental space was converted into the social space. This also had the benefit of orienting the new chapel east/west, which is preferred historically in the Christian faith. The form is driven by the Christian Community’s design guidance for new churches: symmetry, lighting and ‘movement’ along an east-west axis with the internal walls and roof being, paradoxically, calm but ‘lively’.
The design team were inspired by the great mediaeval cathedral builders, where internal form is derived from a perfect fusion of ecclesiastical function and structural efficiency, where stone is used both as structure and internal finish. Whilst it is impractical now to reproduce the inspiring hand crafted mediaeval cathedral structures, we wanted to capture these essential qualities and give them a contemporary interpretation both in terms of the requirements of the Christian Community and the ecological and environmental necessities of the 21st century.
The extensive use of cross-laminated timber (CLT) was driven by three other main factors: the freedom to produce a form in which non-orthogonal geometries could harmonise with structure as in nature, sustainability in carbon sequestration, and the very restricted nature of the sloping site. The design process involved a great deal of client participation with visualisations and workshops, leading to large scale 1:20 physical models from hand sketches exchanged between architect and engineer.
Structurally, the project uses CLT panels in a truly unique and innovative way; a pure, elegant internal form was developed, where ceiling and walls read visually as one entity. Standard sizes of CLT panels were used as ‘folded plates’, like origami, with an elegant structural efficiency obtained by a form geometry which created a lively dynamic feel as well as a timeless stillness. The structural system allows the smooth flow of forces from the vaulted ceiling to the ground. The load is shared with an arrangement of 300mm deep glulam ribs, concealed above the 120mm thick CLT panels at panel joints so as not to visually distract from the religious services within. The predominant load path is an arch which spans 17.5m in the chapel’s long axis with a lateral thrust which is resolved in the chapel walls. Analytical methods were developed by Corbett and Tasker Engineers for the project, using finite element techniques which accurately simulated the flow of forces in the laminated timber panels. Understanding the stiffness of the roof was very important, given the visually exposed soffit – small deflections could cause panel joints to open up and be visible from the underside.
The timber vault is expressed honestly within the church and dramatically highlighted by distinctively shaped side windows. The shape was developed in close collaboration with the acoustician, following the best tradition of cathedral building, and the resonance of music and spoken word was modelled successfully during the project’s design development, informing the final geometry.
Using the latest BIM technology, the erection of the superstructure took 8 weeks – through the winter months of poor weather – despite the complex geometry. Whilst vaulted structural forms are highly structurally efficient, they can be complex to build. Initial thoughts of erecting a birdcage scaffold below the roof would have removed any benefit to the programme that choosing a prefabricated structure would have provided, as well as being a considerable cost to the project. Working closely with the site team, an alternative approach was developed, where the installation of small temporary timber props to the head of the glulam columns and down to the adjacent flat roofs, effectively created three temporary glulam arches over the Chapel.
The embodied carbon footprint of the structure is c. 294kgCO2e/m², excluding sequestered carbon. As a comparison, the London Energy Transformation Initiative Embodied Carbon Primer sets out targets for ‘business as usual’ buildings and the Chapel achieved a c. 40% reduction in embodied energy compared to their current model. This reduction was achieved by the use of sustainably sourced engineered timber as the primary structure, and from minimising the concrete elements in the substructure.
Reverend Tom Ravetz, leader of the Christian Community in the UK, remarked: 'The impression of the space is one of breath-taking beauty and simplicity… I am sure that it will be a wonderful space to worship in.'
Architect: Nicolas Pople Architects
Structural Engineer: Corbett and Tasker
Project Manager: Local Agenda
Mechanical and Electrical Engineer: Hydrock
Quantity Surveyor: Gardiner and Theobold
Below Ground Drainage: Clive Onions
Main Contractor: Beard
Timber Fabricator: Zueblin
Timber Erector: Baucon
Year Completed: 2019
Construction Value: £1.96m
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