Architect and contractor worked together to bring steel-style Kawneer windows to the £17 million rescue of a partly derelict college.
Kawneer's GT70 slimline renovation windows as fixed lights and top-hung casements are complemented by AA®100 curtain walling, AA®541 fixed lights and top-hung casement windows and series 190 doors on the redevelopment of a former Middlesex University site in Enfield, north London.
Now the 1,680-student secondary school and sixth form Heron Hall Academy, the redevelopment comprised the refurbishment, remodelling and extension of an unoccupied 1930s Grade II listed technical college over two years by main contractor Willmott Dixon.
The glazing systems by leading UK manufacturer Kawneer were installed over a year by JPJ Installations - the GT70 windows replacing the original steel windows on the Art Deco façade and the mullion-drained curtain walling, AA®541 windows and series 190 heavy duty commercial entrance doors on the concrete frame extension.
Katie Robinson, project architect with designers ArchitecturePLB, said: "Willmott Dixon had used Kawneer on a previous refurbishment school project and therefore asked us to work with them to develop the designs.
"The Crittall windows are key to the character of the original building and therefore it was fundamental the replacements where faithful to the original design. Window replacement was considered key in meeting current Part L requirements. It was a contentious issue that was much debated with the planners as it was key to making the project affordable."
She added: "Aluminium was chosen due to the need to achieve a thermally-broken double-glazed unit with a narrow profile. We were able to keep the profile of the frames to a minimum and replicate the protruding fins on the original windows.
"We could also achieve a narrow frame depth which enable us to retain the important heritage item of the existing terrazzo cills insitu during the works. These would have broken up if they had needed to be removed."
Katie further added: "The building's glazing is of vital importance to its architectural character but was in a very poor condition. Its single glazing and steel frames precluded retention in teaching spaces where modern environmental performance standards were required.
"Elsewhere however, we were able to preserve and repair key windows. These included the strip windows in non-teaching spaces, the vertical bays to the tower and stairwells and a curved bay in the northern courtyard.
"Where windows had to be replaced, extensive investigations and negotiation with the local heritage officer were required to find an affordable solution that mimicked the frame dimensions of the Crittall originals and allowed retention of the internal terrazzo cills."
In line with current thinking, the new wing was designed to complement rather than replicate the original. Its arrangement reflects that of the original building whereby the major communal spaces, in this case the new dining hall, are arrayed down its centreline to connect the teaching wings to west and east.
It is visually separated from the original by new Kawneer-glazed stairwells while Kawneer ribbon windows were used to reflect the proportions and horizontal emphasis of the listed building.
ArchitecturePLB's alternative design solution, following careful and considered analysis of the site and existing buildings, made the project viable.
Instead of retaining and refurbishing a range of poor-quality one- and two-storey extensions, they proposed their wholesale removal, allowing them to recreate a previously infilled courtyard, reinstating the original plan form, and bringing daylight and views back into the heart of the building.
The removed elements are replaced with a new three-storey block featuring Kawneer's curtain walling and AA®541 windows, purpose-designed to connect the original wings and accommodate new dining and specialist teaching facilities.
Several key areas, including the original entrance lobby, hall and gymnasium have been carefully restored. The reinstatement of the southern courtyard has created additional external play space and brings daylight and sunshine back into the heart of the building, along with views to the outside and improved orientation. The central assembly hall has been returned to its original function and proportions, with a recent mezzanine removed and the stage and proscenium arch reinstated.
The existing listed school buildings were designed to be simple, adaptable and robust. Wherever possible original materials and important features such as the bronze-clad entrance doors were preserved and restored.
Externally, the original brickwork, tiling, cast iron rainwater pipes and concrete window cills and surrounds have been left intact and repaired by specialists where necessary. In line with ArchitecturePLB's "minimum intervention" approach, the decision was made not to clean brickwork to retain its historic patina and avoid highlighting the different brick types used within the existing building.
Although an inherently more expensive solution, ArchitecturePLB's alternative design intensified the efficient use of the site, replacing existing single-storey with new three-storey accommodation. This meant the building took less of the available site, allowing more to be released for residential development.
This creative response to the problem delivered a win-win solution - more space for much-needed housing, a larger proportion of purpose-designed specialist accommodation for the school, and a sustainable future for a fine but neglected heritage asset.
Deputy headteacher Sam Orsborne said: "ArchitecturePLB took on the ideas we had as a school and made them fit with the Art Deco design of the existing building. This was an important design element for us all. We now have a fantastic contrast between existing and new building that is beautifully designed."
The original buildings, designed in the 1930s as a technical college by WT Curtis and HW Burchett of Middlesex County Architect's Department, embody many of the theoretical discussions of modern educational architecture taking place at the time.
The design, form and materials show strong links to Dutch and Scandinavian architecture of the same period, notably that of WM Dudok. This is evident through the large glazed expanses, the central entrance tower and the tiled giant-order columns.
Technically-advanced materials such as steel-style glazing and the ideological alignment of the modern movement would both have been very fitting design choices for an innovative technological institution.
The scheme was shortlisted for a RICS Award 2017 in the conservation category.
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