Director of ASWS (Associated Steel Window Services) Kris Bennell, considers how conserving aluminium window systems can cut cost as well as carbon
As a strong, lightweight and very versatile material, aluminium has seen service for everything from saucepans to the fuselages of supersonic jet aircraft, while also being ubiquitous across the construction industry. Significantly, it is also hailed as one of the most successfully recycled metals, globally – with manufacturers confidently predicting that we will eventually reach the point where mankind will no longer need to expend vast amounts of energy smelting down the world’s abundant reserves of bauxite ore.
Reuse has reached the point where one of Europe’s foremost producers has established a sophisticated supply chain for recovered aluminium, whereby clients can opt to have their shiny new fenestration systems fabricated from ingots certified to contain a minimum 75% recycled material. This approach consumes a fraction of the energy – renewable or otherwise – needed to produce virgin stock. In refurbishment situations, however, should project teams be seeking an even more sustainable solution?
An increasing number of developers and their design consultants are coming to understand the genuine value of retaining as much as possible of existing properties, even where they are not subject to conservation requirements. They are understanding that reuse can offer the lowest environmental footprint and potentially significant budget savings. While this ethos is well established with regard to steel and even century old timber windows, the poor reputation of early aluminium windows – whose surfaces frequently pitted and became powdery – is such that replacement is the default position for most developers.
Surveys & thermal performance
Undertaking condition surveys pre-contract can pay dividends. Judging the viability of retaining and restoring the eclectic mix of 20th century aluminium window systems will be beyond the expertise of most architectural practices, and it is therefore always circumspect to call on the services of an experienced metal window repair specialist to carry out a detailed condition survey. Ideally their report will encompass precise measurements, photographs and drawings, along with a schedule of works being recommended. This document can be not only the basis on which to source tenders, but could also form the part of the planning submissions; carrying significant weight with councils who are increasingly prioritising sustainability across any such work being carried out in their areas.
Unavailable when the first aluminium frames started to replace often rotten timber windows, thermal breaks radically improved the U-values delivered by most systems installed from the eighties onwards. But these slender plastic strips separating the inner and outer profiles are, of course, only part of the overall energy performance picture.
Retained frames with fixed and opening lights can be greatly improved by retrofitting modern gas filled IG units, featuring low-e glass and warm-edge spacer bars. But improving airtightness by upgrading the seals or draught-stripping can be just as important. This, however, can be a very difficult task when working insitu, even once appropriate new gaskets have been sourced. In many instances it proves necessary for specialist sub-contractor to replace the original factory fitted rubber glazing gaskets with manually applied silicone top caps, both internally and externally.
Achieving good airtightness can also depend on the window contractor having the right skillset to realign or reset the frames, and either overhauling or sourcing compatible replacements for the original handles and other hardware.
In some cases, the company may actually keep a physical archive of salvaged ironmongery which will suit, or at least have the industry contacts to obtain compatible fittings in a timely manner. Also, where significant physical damage has occurred, the extent of the repairs may even involve having to cut out and replace sections of the original frame and being able to cosmetically conceal this remedial work.
Cutting waste
During the pandemic, we helped deliver an integrated repair contract for a regular clients as part of the redevelopment of a landmark London office property. It not only enjoys some of the best views in the capital overlooking Hyde Park, but also now offers sustainability credentials in excess of those benchmarked by the GLA for new-build offices. Completed in 2022, the reconfiguration of No 1 Knightsbridge was led by ISG and has created spacious floorplates totalling 122,000 ft2 of Grade A space that benefits from low embodied carbon and an all-electric building services package. Pragmatic repair and recycling also meant 99% of all the strip-out material was diverted from landfill, contributing to the scheme earning a BREEAM Excellent rating.
We carried out a full condition survey on all of the existing fenestration, which featured outmoded aluminium windows and curtain walling, and were awarded the full overhaul contract as well as work such as servicing the rooftop smoke vents, and the installation of a large glazed light in the courtyard atrium. The complex geometry of the building and the number of different trades on site required both weekend working and the expert use of both access and tele-handling equipment. Repairs to the 1980s aluminium windows and curtain walling included replacing damaged sections as well as the filling and respraying of frames across all floors, both internally and externally.
Kris Bennell is director of Associated Steel Window Services