How we decarbonised Wolfson College’s brutalist buildings

The challenge

The Powell & Moya-designed buildings for Oxford University’s Wolfson College were constructed between 1969 and 1974 and did not perform well environmentally. Building envelopes were thermally ineffective and services systems antiquated.

Wolfson is a graduate college, established in 1966 with the aim of combining modern values with academic excellence, providing graduate students and fellows with an egalitarian home by the River Cherwell.

The college's distinctive brutalist buildings were completed in 1974, the same year Powell & Moya won the Royal Gold Medal for Architecture. The buildings were designed to provide functional, high-quality accommodation for graduate students and fellows, and to create a sense of community and social engagement. The college's architecture reflects its commitment to modernity and innovation and is recognised in its Grade II listing.

Wolfson nevertheless acknowledged that its carbon footprint was a significant concern and has taken steps to reduce its impact on the environment. In 2020, the college calculated that, if it did nothing, it would have a 20-year carbon footprint of at least 24,000 tonnes. In its 2020 Estate Strategy, the college made decarbonisation its top priority.

Given its unique architecture, original 50-year-old gas heating system and large single-glazed windows, decarbonising Wolfson's estate presented a complex and costly endeavour. Its architectural uniqueness and historical significance made any changes or upgrades more challenging. Despite this, the college made it a priority to maintain full operations during the project, which added significant complexity given the impact of the works on all areas of the functioning campus. One of the major project risks was the use of the existing heating system across the expansive building complex. Extensive surveys were conducted to map and analyse the system to inform the design proposal and reduce potential risks.

The approach

Building services engineer Max Fordham completed an energy audit and decarbonisation plan for the college. This established that the combined fabric upgrades, including window replacement and insulation, would reduce the buildings’ annual space heating requirement by at least 80 per cent. In addition, replacing the gas boilers with modern heat pumps to provide heating and hot water would reduce the main estate’s 20-year carbon footprint by at least 75 per cent. A design team was assembled with Max Fordham designing the mechanical and electrical systems and Oxford-based Original Field Architecture & Landscape working on the architecture including planning, building fabric enhancements and project coordination.

In the summer of 2021, the college was awarded a £5 million grant from the Department of Business, Energy and Industrial Strategy’s Phase 2 Public Sector Decarbonisation Scheme. This specifically aims to encourage a reduction in heating system-generated carbon. The college matched the government grant with an additional £3 million from its own reserves. The government funding had to be used within a single year, meaning that the enabling stages had to be in place before the grant was paid.

At the outset, Max Fordham reviewed strategies for the heating system. As the existing pipework and radiators needed to be retained to keep the project viable, it opted for an air-source heat pump system with a sealed CO₂ refrigerant. This is one of the largest CO₂ heat pump programmes undertaken in the UK and one of the largest to be retrofitted to an estate of this complexity.

The replacement of gas-fired boilers with heat pumps and electric boilers meant the estate’s electrical supply needed to be upgraded from 400kVA to 1200kVA along with the routing of cables from the upgraded transformer to the heat pumps.

Early in the project, Original Field engaged with a number of local and consultative authorities, including Oxford City Council, Historic England and the Twentieth Century Society. Unsurprisingly, window replacement became the primary focus of attention, in particular the ability to reproduce the slim sight lines and maintain the intent of Powell & Moya’s original design, balanced against the need for high-performance thermal windows. There are over 1,000 windows in the buildings, and the proposals called for these original aluminium-framed single-glazed windows to be replaced with replica configurations and operations. Following extensive research within the industry, the project team selected a system of high-performance thermally broken aluminium frames with triple-glazed Cuin glass. These have a low mid-pane U-value of 0.4 W/m²K with an overall thickness of 28mm.

Original Field also assessed the internal layouts and room arrangements. The original design incorporated radiators below window benches. Thermablok Aerogel, an ultra-thin breathable insulation, was sourced to upgrade the performance of the remaining in-situ concrete and masonry external facade areas surrounding the windows. This provided the thinnest insulation possible, eliminating cold bridging with minimum impact on the wall-to-wall glazing.

To accommodate the need for a production-line approach for the four-day access to rooms during installation, the project required a unique and flexible procurement strategy. Rolling out this approach across the site for a year presented several challenges that necessitated a collaborative problem-solving approach. One significant issue was the limited amount of exploratory work possible in advance of the project start. Extensive examination of original detail drawings was necessary to predict the building arrangement after removing the existing windows. However, the original building's variations in detailing during its construction resulted in many unforeseen challenges that had to be overcome through careful on-site detailing and adaptation.

The result

The new heating system and fabric upgrades to the original college buildings were completed in 2022. Presently the college is decarbonising its subsidiary estate which involves the upgrade of the houses surrounding the main college. Once the decarbonisation projects are complete the college is on course to achieve net zero and reduce the carbon emissions by >80% with typical grid electricity. With a supply of renewable electricity, the College will be net zero carbon for its Scope-1 and Scope-2 emissions once these projects are complete.

The project is world-leading in its delicate treatment of an historically significant piece of modern architecture that will be made net zero with no impact to its aesthetic and design excellence.

As such, the project has been awarded an Oxford Preservation Trust Green Award in 2022. This award recognises buildings and environmental projects which offer an outstanding contribution to the character of Oxford. The success of the project is attributed to the contributions of a devoted project team who worked collaboratively together. Recognition should be made for the ongoing support and trust of the college Bursar and Committee for leading on this ambitious project to retain a seminal piece of English Brutalist architecture updated for 21st century living, centred on environmental consciousness.

Next Steps

While the college is moving towards zero carbon, it aspires to further minimise energy consumption, planning to install additional photovoltaic panels on roofs to generate electricity as well as adding insulation to uninsulated original flat roofs.

It has already installed photovoltaic panels covering 135m² of roof area. By installing more panels on all suitable roofs (a total of 980m²), it hopes to locally generate about 10 per cent of its total energy demands.

The college is also planning to install a new 1MWh electrical storage battery. This would allow it to draw electricity at peak ‘green’ times, and store energy for use later.

Andrew Dawson is director of Original Field of Architecture & Landscape