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isg leading the way with "green retrofit" of 1930s building in cambridge.

Sustainability by example

"This is not an ordinary project, but it needs to be."

These are the words on hoardings that surround a former 1930s telephone exchange in Cambridge. Pioneers in sustainability understand the importance of leading by example and that's precisely what the Cambridge Institute for Sustainability Leadership (CISL) is doing. Part of Cambridge University, CISL needed to move out of its Trumpington Street headquarters into new offices. Faced with the inevitable clash between its values and the polluting reality of traditional construction methods, it opted for a refurbishment and retrofit.

The building on the corner of Regent Street, although nearly 100 years old, is structurally sound and has been used as offices for the past 30 years. Instead of demolition and rebuilding, CISL decided to work with ISG to develop an innovative plan to convert 1 Regent Street into Entopia. The building's new name is a combination of the first syllable of Envision, a manufacturer of batteries for electric cars, who have donated £6 million to the project, and the word Utopia.

The total cost of the green retrofit is expected to edge towards £13 million. The work is being carried out to the PassivHaus EnerPHit standard. CISL's other objectives are to achieve WELL Gold certification and a BREEAM rating of Outstanding. The success of the refurbishment will stand as a practical demonstration to the construction industry that sustainability is economically viable, and that retrofitting existing buildings to the highest international standards should become the default option in creating new commercial, industrial and domestic space.

One of CISL's aims is to meet a carbon target of 300kg/CO2/m² to be maintained for at least 100 years, including the materials used in all refurbishment, maintenance, repair and eventual deconstruction. Another objective is to use at least 50% bio-based materials in the retrofit, which means that any use of petrochemical products must be kept to a minimum.

The project has not been without its challenges and obstacles. The EnerPHit insulation requirements proved exacting because the building is in a conservation area, rendering external insulation impractical. Additionally, the neo-Georgian multi-paned sash windows leaked heat, but the planning officers initially insisted they must be retained. Fortunately for CISL the planning committee could see beyond this aesthetic concern, and approved plans to replace them with large, tilt-turn windows to increase the level of natural light and offer greater thermal performance.

Explaining this controversial decision the sustainable buildings adviser for Cambridge University estate management, Alex Reeve, said: "One of the reasons for approval was this was an exemplary project that was addressing the climate emergency."

Another problem arose in discovering precisely how the building had been instructed, an understanding of which is vital to any retrofit work. The variety of construction methods made the application of internal insulation difficult. The building has a concrete frame, floor slabs and 300mm brick walls, several concrete columns were in poor condition and others, made of steel, were encased in concrete.

For ISG the pre-construction process was key to the entire project. The contractor effectively deconstructed the building to determine would could be retained and reused rather than responding to the reflexive instinct to rip out and replace. This even extended to redeploying 350 LED light fittings removed from a London office.

Once this phase was complete it was clear that many modern materials would not be appropriate, and therefore niche suppliers had to be used. This created the risk of simply not being able to source materials in sufficient quantities. Here again the project hopes to encourage and enable the use of such non-traditional construction products, including bio-based materials. Chris Chappell, contracts director at ISG, said: "We want to promote the wider use of those materials as this will improve availability and drive the economies of scale which will drive better-value building retrofit."

The eyes of the industry should be watching Entopia very closely because it may represent the future.


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