The first project of its kind in the UK, the decarbonisation of Oxford University’s Wolfson College set the unique challenge of achieving net zero carbon in a Grade II-listed piece of Brutalist architecture.

At the project's outset, the graduate college had a 20-year carbon footprint of ~24,000 tonnes of CO2 across their 15,000m2 GIA buildings. Today, after an extensive refurbishment that figure has reduced by more than 500 tonnes in the first year of occupation. We expect the annual carbon emissions in the buildings to reduce to zero next year, bringing the college on course to achieve net zero carbon – well ahead of their 2030 target.

We initially undertook a study into carbon-saving measures and discussed the range of options and their carbon savings with the college. The building’s 50-year-old gas heating system, its extensive single-glazed windows and its status as a work of architectural and historical significance posed a significant challenge.

Following the study, we produced a Decarbonisation Plan that recommended:

• Changing the single glazing to triple glazing
• Reusing and adapting the existing gas-fired heating system to work with electric heat pumps - two large at 350kW and five small at 15kW
• Replacing the roofs and installing maximum insulation
• Upgrading all lighting to LED
• Installing PVs on the new roofs and installing a 1MWh electrical storage battery.

To keep disruption, cost and embodied carbon to a minimum, we devised a strategy to keep the existing radiators and pipework and worked with the college to ensure it could be occupied throughout the programme of upgrades. We opted for an air-source heat pump system, using an innovative low environmental impact CO2 refrigerant (rather than a more damaging refrigerant). The project is one of the largest CO2 heat pump programmes undertaken in the UK and one of the first to use CO2refrigeration for space heating at this scale. We have also made many rationalisations to the mechanical systems to reduce energy consumption more generally – radically reducing pump sizes and the extent of distribution pipes.

High planning and heritage standards for the Grade II-listed building meant that choosing the correct glazing was crucial. Following extensive research by the architect Original Field of Architecture, the team opted for Cuin glass, a material that has the performance of triple glazing with the thickness of double. This allowed the heritage sightlines to be preserved without compromising the aesthetic of the building while achieving excellent thermal performance.

The college has been implementing these improvements in phases. The initial phase involved replacing almost all the windows in the original 1972 listed building complex and switching its heating system from gas boilers to electric heat pumps, completed in late summer 2022. The college has since been decarbonising the rest of its estate, which involves upgrading its surrounding houses and adding some other, newer accommodation buildings to the main heating system.

Once the decarbonisation projects are complete the college will no longer have fossil fuel combustion in its buildings and will be on course to achieve net zero. Our calculations established that replacing windows, roofs and insulation alone has reduced the buildings’ annual heat losses by 80%.

Energy consumption data over the first year shows that gas consumption has reduced by more than 60%, while electricity consumption has barely increased. The losses in the hot water distribution system have reduced by 40%. So far, the reduction in pumping energy has largely offset the additional electricity consumption of the heat pumps

The total reduction in carbon emissions would be calculated to be more than 80% over the next 20 years, however the College procures 100% renewable electricity and so the reduction is 100%.

The RIBAJ has described the project as ‘world-leading in its delicate treatment of an historically significant piece of modern architecture that will be made net zero carbon with no impact to its aesthetic and design excellence.’

In addition, we led the college’s successful application to secure £6M of SALIX Grant funding, which covered 65% of the first phase works and some proportion of the second phase. We are working with the college to help them promote and explain the project to their residents and alumni, to help them secure support for the later phases of the work.

Read more about the SALIX funding process for Wolfson College in our Net Zero Carbon Guide.