Purcell’s expansion of Radley College’s Grade II*-listed chapel includes a new sanctuary with an octagonal plan form and roof lantern formed of self-supporting curved structural glass

Radley College is an independent boarding school for 690 boys aged 13-18, founded in 1847 by the Reverends W Sewell and RC Singleton with the aim of providing a quality Church of England education against a ‘background of cultural influence in aesthetic surroundings’.

The chapel is the only place where the whole school congregates and is therefore intensely used. Daily services are a cherished part of student life. Radley was looking to expand its intake and offer more assisted places. However, the school was already squeezing into the Grade II*-listed chapel (by TG Jackson, 1893) and so the sustained use of the building for this important tradition was at risk. The expansion of the school hinged on the expansion of the chapel and the continued ability of the school to gather as one.

A series of localised extensions were proposed that respected the integrity of the collegiate chapel form, retaining the clerestory and stained glass windows. The primary intervention to the east end provided space for the sanctuary and the opportunity for reordering. The new sanctuary has an octagonal plan form, approached through a series of stone and rubbed brick arches from the nave. A sequence of apses on the north and south elevations achieves three additional rows of seats. The sense of procession is reinforced by the synergy between ritual and architecture, and we sought to ensure that the relationship between these was equally important within the proposals. Our scheme delivers an additional 207 seats to provide a total of 807. Josh Greig, associate, Purcell

Start on site September 2019 Completion July 2021 Gross internal floor area 450m2 (existing) + 570m2 (proposed, including gallery extension) Construction cost Undisclosed Architect Purcell Client Radley College Structural engineer Campbell Reith M&E consultant Hoare Lea Cost consultant Ridge and Partners Principal designer Ridge and Partners Approved building inspector NHBC Main contractor Beard Construction Planning consultant Edgars Organ consultant Paul Hale Heritage consultant Heritage Collective Landscape consultant Colvin and Moggridge CAD software used Revit Predicted design life 100+ years

The new extensions are a conscious continuation of Jackson’s design, with their own contemporary character and presence. The architectural detailing, scale and proportion of the extensions were driven by the same sense of design unity and the materials selection was used to bind the existing and proposed elements together.

All materials were selected early in the process, generally during RIBA Stage 3, which allowed for time to refine and adapt finishes. From the windows to the stone, the defining factor in the specification was to create a sense of unity with the existing chapel and, where possible, to find local suppliers and specialists. Josh Greig, associate, Purcell

We developed a complex bespoke door design which required a discrete spandrel panel at the top and side, due to the difference in internal and external geometry. It incorporated Lorient weatherstrip, threshold and drop-seal details to ensure it was weathertight.

The college worked closely with York Glaziers Trust to develop the painted glass windows, which are a striking and integral part of the scheme. The design of these picks up on many of the college symbols, such as the crossed keys of St Peter, as well as other biblical symbols. The windows were installed in steel frames made by Cotswold Casements. The installation was completed with a through-colour silicone finish in preference to putty.

The key technical challenge with respect to the windows was the height and proportion of the glazing and stone mullions. The approach we took was firstly to stabilise the mullions with ferramenta, positioned at the bed joints. The ferramenta tied together horizontally as well as between the internal and external mullions. Vertically, these aligned with the saddle bars. In addition, we installed 32mm-deep SMW frames and a 25mm thermal break. High-density Compacfoam insulation was used to provide a vertical DPC that could be fixed into directly. Although it is not typically used in an application of this kind, we undertook testing to establish that it satisfied the requirements.

Having explored a number of options for the roof lantern using curved glass or glass shingles, we developed the design to be a self-supporting triangulated convex curve. While there is some structure below the glazing, it is not technically required, as the structural glass supports itself. We worked closely with the manufacturer, L2i, to develop the detailing at RIBA Stage 4. Josh Greig, associate, Purcell

Doors D Smith Joinery Bespoke oak doors constructed from 25mm-deep horizontal oak boards with 3mm check gap detail at joints External doors to sanctuary

Windows (frames and leaded lights) Cotswold Casements Sanctuary and Apse steel windows constructed from the SMW range Windows to sanctuary and apses cotswold-casements.co.uk

Windows (painted glass) York Glaziers Trust Bespoke painted glass, designed and installed by York Glaziers Trust Sanctuary windows yorkglazierstrust.org

Octagonal roof lantern L2i (using Schüco system) Bespoke self-supporting structurally glazed roof lantern consisting of 64 individual panels in a convex curve Sanctuary l2iltd.co.uk

Bricks Northcot Bricks Package of 87 different types of brick, requiring over 50 different moulds to form Internal and external walls northcotbrick.co.uk

Bricks Lambs Bricks TLB Red Rubber Brick, Code RR Colour Medium East end arch lambsbricks.com

Stone Cadeby stone Natural limestone, bedded on NHL 3.5 mortar (5.0 to parapet), and anchored using 316 stainless steel dowels Internal and external walls ogstonemasonry.co.uk

Roof structure Carpenter Oak Bespoke octagonal trussed oak structure Sanctuary roof carpenteroak.com

Roof finish Attleys Roofing Cast lead shingles, tapered from 2.5mm to 20mm thick Sanctuary roof attleysroofing.co.uk

Joinery D Smith Joinery Bespoke pews made from European oak Nave

Floor finish (to match existing) Janatti MGT White Carrara C Marble and Nero Marquina Marble Ground floor jmgt.co.uk

Tags Chapel doors and windows Purcell

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