College renovation

Architect and contractor worked together to bring steel-style Kawneer windows to the £17 million rescue of a partly derelict college – now the 1,680-student secondary school and sixth form Heron Hall Academy.

Kawneer’s GT70 slimline renovation windows as fixed lights and top-hung casements were complemented by AA100 curtain walling, AA541 fixed lights and top-hung casement windows and series 190 doors on the redevelopment of a former Middlesex University site in Enfield, north London.

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, AA541 windows and series 190 heavy duty commercial entrance doors on the concrete frame extension.

Katie Robinson, project architect with designers ArchitecturePLB, said: “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.

“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.

“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.”

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.

Instead of retaining and refurbishing a range of poor-quality one- and two-storey extensions, ArchitecturePLB 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 AA541 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 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 scheme was shortlisted for a RICS Award 2017 in the conservation category.