100 NET ZERO
RETROFITTING HERITAGE PROPERTY to net zero is like seeking world peace – everyone thinks it’s a great idea, but how to achieve it is another question entirely. With nearly a third of commercial property in the UK built before 1919, the scale of the problem is vast – and the cost even more so, with the government’s adviser, the Climate Change Committee, estimating that meeting the UK’s target of net zero by 2050 will cost £1.4trn.
Despite the cost and difficulty involved, many architects are feeling positive. ‘It’s good that we’re all talking about it,’ says David Weatherhead, senior design principal at HOK. ‘Our urban fabric is full of important buildings, the quality tends to be high and they have been built to last. Churches aside, not many historic buildings today are still in the use they were designed for, but we can find a new use for that quality and robustness.’ Nuno Correia, head of sustainability at WilkinsonEyre, agrees: ‘Retrofitting our existing building stock is absolutely essential to decarbonising the built environment and achieving net zero carbon.’
While creating a new net-zero building is straightforward, transforming heritage buildings presents greater challenges. ‘It requires a case-by-case approach considering whole-life carbon, with an understanding that embodied carbon is a key contributory factor,’ says Correia. ‘Heritage building envelopes and their materials present highly complex issues associated with improving fabric performance. Tere is a need to balance reasonable interventions with an understanding of the significance of these buildings; their accrued cultural and historical value – which represent less tangible, but still important, facets of sustainability.’ ‘Not all buildings are net-zero retrofit candidates,’ admits Phillip White, associate principal at CO Architects. ‘Certain buildings may have historic or cultural value, and the energy improvement would undermine the building’s character-defining features – historic single-pane windows being one example. In these cases, project teams should try to offset those signature features by supplementing and improving the efficiency in other areas, such as providing super- insulated exterior wall assemblies.’ ‘For any refurbishment or repurposing of historic buildings, it is first necessary to understand the significance, whether historical, architectural or cultural,’ says Chris Davies, head of conservation at WilkinsonEyre. ‘Termal upgrades and improvements to the operational energy have to be weighed against the harm they might cause to this special interest. We have to resist net zero at any cost because we, as a
society, still choose to highly value our historic buildings, which stand somewhat outside conventional economic reckoning. Historic buildings are best maintained when they are occupied and this is only possible within the real-world conditions of a viable, long-term, use.’
It’s a conundrum that is particularly relevant to custodians of the UK’s historic churches. Te United Reformed Church, Church of England and other denominations
have committed themselves to reaching net zero even earlier than the politicians – by 2030. Clifford Patten, director at Lewis Patten Architects and member of the United Reformed Church Net Zero Task Group, explains: ‘Tere is a degree of understanding that the timescale, ongoing technological developments and funds available make this an unrealistic task, but it has been set with a strong belief that this is what the Church is being called to do. Churches would say that
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