The conversation around the UK’s built heritage needs to move beyond chat about architectural splendour and cute historical oddities. Our legacy of Georgian townhouses and Victorian terraces, medieval churches and post-war listed structures make up a significant 20% of our building stock. With the scramble for net-zero targets, they have become a place where the will to save the planet by decarbonising our built environment is coming into head-on collision with the equally powerful need to preserve our built heritage. This is not something that is going to be resolved through technical ingenuity or a trickledown of better policy. This is a fundamental conversation about values, about permanence, and about what we owe to the future and to the past.
The Solid Wall Conundrum: A Building Physics Problem
The challenge begins with a building physics problem. The vast majority of the UK’s historic building stock was constructed with solid walls. Brick, stone, cob… walls that breathe and allow moisture to pass through them. Current energy efficiency standards, however, were created for buildings with cavity wall construction, where insulation lives happily between two leaves of brickwork. Attempting to retrofit modern insulation strategies onto solid-walled historic buildings is not only technically complex; it is actively damaging.
“Once you start messing around with the hygrothermal performance of a solid wall, you’re in dangerous territory,” Sarah Wigglesworth tells me from her practice’s offices in London. “These buildings have been here for hundreds of years because they are inherently able to cope with moisture in a specific way. Trap it inside the fabric and you’re asking for problems. Problems that can lead to catastrophic decay of the very thing you’re trying to save.”
The options for insulating solid walls are limited, and all come with a degree of compromise. External wall insulation (EWI) can radically change the appearance of a building, masking architectural features, distorting proportions and generally wiping out the character which is what makes a building worthy of protection in the first place. EWI is mostly not an option for listed buildings, or for any building in a conservation area. Internal wall insulation (IWI) at least solves the problem of external appearance but comes at the cost of reduced internal floor area, potential thermal bridging at junctions, and—crucially—the creation of a moisture management regime that the wall was not originally designed to cope with.
The Sustainable Traditional Buildings Alliance (STBA) was formed in 2012 in order to start building bridges between the conservation and sustainability sectors. They have since run and published an ambitious programme of research and case studies on the performance of different insulation systems in traditional buildings. Their findings are a world away from the reductive solutions often espoused by energy efficiency policy. “What we’re finding is that traditional buildings need traditional solutions, or at least they need solutions that understand traditional building physics,” Dr Joseph Little tells me, with a depth of experience of working with the STBA on traditional building moisture management. “Breathable insulation materials, lime-based renders, wood fibre boards, sheep’s wool can all work, but they need to be carefully specified, expertly installed and managed with a view to realistic performance levels.”
The ethical component of this problem isn’t merely a technical one. Insulating a historic building is an irreversible intervention. It is a statement of values; the prioritisation of carbon reduction, energy efficiency, thermal comfort over a set of alternative values around material authenticity, historical integrity, architectural legibility. In some cases, that trade-off is perhaps warranted. In others, it is a form of vandalism to our cultural heritage masked in the language of climate action.
The Renewable Energy Paradox
If insulation is a problem of nuance and compromise, the integration of renewable energy technologies in historic buildings and landscapes is often a problem of visual offence. Solar photovoltaic panels, heat pumps, and wind turbines are the de rigueur symbols of the energy transition but their aesthetic is undeniably, resolutely contemporary. Placing them on, or even near, historic buildings sets up an immediate visual clash.
Take the roofscape of a Georgian terrace. Slate or tile in carefully proportioned courses, chimneys and parapets providing an emphatic crowning flourish to the elevation. Solar panels disrupt that designed composition at a fundamental level. They create a visual and material language that is fundamentally different from the traditional construction, with a different geometry, different ratios, a different way of dealing with light. On a listed building or in a conservation area, planning authorities will be required to do a planning balancing act of the public carbon reduction good against the harm to heritage significance. Rarely is that process simple.
Max Fordham LLP has been a leading light in the integration of environmental services into sensitive buildings since its foundation in 1966. From work on pioneering projects like the Stirling Prize-winning Accordia housing development to its recent retrofit of the historic St Alban’s Hospice buildings, it has a unique perspective on the problem. “The question we ask when we start any project is: what is this building telling us about the way it wants to perform?” a senior partner explains, when we meet at the practice’s Clerkenwell offices. “Historic buildings have an environmental strategy that was designed into them before we had the language of sustainability to describe it. Thermal mass, natural ventilation, solar orientation. Sometimes the best intervention is the least.”
Heat pumps offer a different range of problems. Air source heat pumps (ASHP) are the most common form, but they need external units which create noise and visual impact. They work best with low-temperature heating systems—underfloor heating or overscaled radiators—which are difficult to retrofit to historic interiors without significant change. Ground source heat pumps (GSHP) avoid the issue of the external unit but require extensive groundworks which have the potential to damage archaeology or historic landscapes.
The Passivhaus Trust is best known for its work on new ultra-low energy buildings but has developed a standard specifically for retrofits, EnerPHit. The standard recognises that it is often impossible, or inappropriate, to achieve the full Passivhaus standard in existing buildings, especially those of historic value. EnerPHit allows for higher energy use but still represents a significant improvement on pre-retrofit performance. “EnerPHit understands that context is important,” a Trust spokesperson tells me. “If you can deliver a 70% reduction in energy use in a listed building, with a reasonable environmental and heritage package, that is more important—both environmentally and culturally—than achieving a 90% reduction which erases heritage value.”
EnerPHit, with its more nuanced approach, still finds itself challenged by the reality of historic construction. The standard still demands high levels of airtightness, which can be difficult to achieve in buildings with solid walls and traditional joinery. The fitting of mechanical ventilation with heat recovery (MVHR) systems, a staple of the Passivhaus methodology, also requires ductwork which is difficult to introduce sensitively.
Whole Life Carbon: The Building That Already Exists
Perhaps the most powerful argument for a more nuanced approach to historic building retrofit comes from the concept of whole life carbon. This methodology looks beyond operational carbon—the emissions from heating, cooling and powering a building—to include embodied carbon: the emissions associated with materials, construction, maintenance and eventual demolition.
When we demolish a building, even one that performs poorly from an energy perspective, we write off all the embodied carbon in its structure. We also create demand for new materials, each with their own carbon footprint. Concrete, steel and brick are carbon-intensive to produce. Even timber, often promoted as a low-carbon material, has a carbon cost in harvesting, processing and transport.
Historic buildings represent vast repositories of embodied carbon. A Victorian terrace house contains thousands of bricks, each fired in a kiln. It contains timber joists and floorboards, slate or tile roofing, lime mortar, and plaster. All of this material has already been extracted, processed and assembled. From a whole life carbon perspective, the greenest building is often the one that already exists.
Research by Historic England has demonstrated that even relatively modest improvements to the energy performance of historic buildings—draught-proofing, secondary glazing, heating controls, loft insulation where appropriate—can deliver significant carbon savings without the embodied carbon cost of more invasive interventions. Their guidance emphasises a “whole building approach” that considers the building as a system rather than a collection of elements to be upgraded in isolation.
“There’s a tendency in policy to focus on operational carbon because it’s easier to measure and regulate,” observes Dr. Fionn Stevenson, whose research at the University of Sheffield has examined the performance gap between predicted and actual energy use in retrofitted buildings. “But when you look at whole life carbon, particularly over the 60-year assessment period now recommended, the picture changes dramatically. Keeping a building in use, even with modest improvements, often has a lower carbon impact than demolition and replacement, even with a highly efficient new building.”
This argument becomes even stronger when we consider the cultural and social value of historic buildings. These structures provide continuity, identity and a sense of place. They embody craftsmanship and material quality that is often impossible to replicate economically today. They contribute to the character of neighbourhoods and cities in ways that new buildings, however well-designed, cannot immediately match.
The Policy Disconnect
Despite growing recognition of these complexities among specialists, policy often lags behind. The UK’s approach to energy efficiency in buildings has been characterised by targets and standards developed primarily for new construction or straightforward retrofits of post-1945 housing. The Energy Performance Certificate (EPC) system, for instance, struggles to accurately assess the performance of traditional buildings. It penalises solid walls and single glazing without accounting for thermal mass, natural ventilation strategies or the risks of inappropriate intervention.
This creates perverse incentives. Landlords of historic properties face pressure to improve EPC ratings to meet minimum standards, potentially driving interventions that damage building fabric or create unintended consequences. The Minimum Energy Efficiency Standards (MEES) regulations, which require private rented properties to achieve at least an EPC rating of E, have created particular challenges for owners of traditional buildings.
“We’re seeing cases where landlords are being advised to install measures that we know are inappropriate for the building type, simply to tick a box on an EPC assessment,” reports a conservation officer from a major local authority. “The assessment methodology doesn’t understand traditional construction, so it recommends interventions that can actually make the building perform worse in reality, even if they improve the theoretical rating.”
There are signs of policy evolution. Historic England’s guidance documents, particularly “Energy Efficiency and Historic Buildings: How to Improve Energy Efficiency” and “Traditional Windows: Their Care, Repair and Upgrading,” provide nuanced advice that acknowledges the complexity of retrofit decisions. The STBA has worked with the government to develop more appropriate assessment methodologies. Some local authorities have developed supplementary planning guidance that provides clearer frameworks for balancing heritage and energy considerations.
But the fundamental tension remains. National carbon targets are expressed in absolute terms and driven by climate urgency. Heritage protection operates through a framework of significance, harm and public benefit that requires case-by-case judgment. Reconciling these approaches requires a level of sophistication that is often absent from policy implementation.
The Skills Crisis
Even where appropriate technical solutions exist and policy frameworks allow for sensitive intervention, a critical bottleneck remains: skills. The traditional building skills required to work sensitively with historic structures—lime plastering, stone masonry, timber frame repair, traditional glazing—have been in decline for decades. Simultaneously, the emerging skills of low-energy retrofit—airtightness detailing, thermal bridge analysis, hygrothermal modelling—are concentrated in a relatively small pool of specialists.
The intersection of these skill sets—practitioners who understand both traditional construction and building physics—is smaller still. “We’re asking for a combination of knowledge that’s quite rare,” acknowledges an architect who specialises in historic building retrofit. “You need to understand how a building was originally designed to perform, how it has been altered over time, how it currently performs, and how proposed interventions will affect that performance. You need to know traditional materials and modern building science. It’s a tall order.”
Training programmes are beginning to address this gap. The STBA runs workshops and produces guidance. Universities are developing postgraduate programmes in sustainable heritage. The Passivhaus Trust has created training specifically focused on retrofit. But scaling up this expertise to meet the challenge of retrofitting millions of historic buildings remains a formidable challenge.
A Way Forward: Pragmatism and Patience
If there is a path through this thicket of competing demands, it likely lies in embracing complexity rather than seeking simple solutions. This means accepting that different buildings will require different approaches, that trade-offs are inevitable, and that perfection may be the enemy of good.
For some historic buildings – particularly those of the highest significance to UK conservation architects – the priority must be preservation, with energy improvements limited to measures that do not compromise heritage value. For others, more substantial intervention may be justified, particularly where buildings have already been significantly altered or where heritage significance is lower. The key is making these decisions consciously, with full understanding of the implications. It means investing in research to better understand how traditional buildings actually perform, rather than relying on theoretical models developed for modern construction. It means developing assessment tools that can capture the nuances of traditional construction. It means training a new generation of practitioners who can navigate the intersection of heritage and sustainability.
Most fundamentally, it means recognising that the challenge of making historic buildings net-zero is not primarily technical. It is cultural, ethical and political. It requires us to articulate what we value and why, to make difficult choices about priorities, and to accept that some tensions may not be fully resolvable.
The historic buildings that line our streets and define our cities are not obstacles to the energy transition. They are part of the solution—repositories of embodied carbon, exemplars of durability and reminders that buildings can be valued and maintained across generations. The challenge is not to make them conform to standards designed for new construction, but to develop approaches that respect their particular character while contributing to carbon reduction.
This will require patience, nuance and a willingness to accept that progress may be incremental rather than revolutionary. But the alternative—a crude application of contemporary standards that damages or destroys what makes these buildings significant—would represent a double failure: environmental and cultural. We can do better. We must do better. The buildings that have sheltered generations before us deserve nothing less.
Heritage Architects: A bridge between two worlds
Occupying the middle ground between the polarising forces of conservation and decarbonisation are a distinct class of practitioner: heritage architects. These specialists find themselves uniquely placed within the retrofit challenge, straddling both spheres of interest. In recent years, the role of heritage architects has expanded significantly, with an increasing emphasis on not just preserving but actively integrating sustainability into conservation practice.
Heritage architects are adept at reading the stories embedded within historic building fabric. They can decipher design intentions from centuries-old weathering patterns, construction techniques, and material choices. They know how the social, economic, and technological contexts of different eras have influenced the evolution of buildings, as well as how to account for the myriad layers of change, alteration, and adaptation that are stacked up within older properties. All of this accumulated knowledge is crucial for understanding how and where to intervene.
“Every old building is like a palimpsest,” says Lisa Mackenzie, a conservation architect with over 20 years’ experience working on listed buildings across the UK. “You’re not just looking at the original fabric but centuries of living with a building, repairing it, adapting it, and improving it. Understanding that evolution is key to designing interventions that won’t do damage.”
But heritage architects are also being increasingly asked to bring a second, equally specialised body of knowledge to bear on their work: building performance and environmental design. They need to be able to understand U-values, thermal bridging, air permeability, moisture transport, heating system design, and renewable energy technologies. They need to be able to model interventions, predict performance, and understand risk. In short, they must also become fluent in the building science required to decarbonise building stock. It is this capacity to blend the two worlds – the knowledge of historical context with the technical know-how for environmental design – that gives heritage architects their value in the retrofit challenge.
The best UK heritage architects adopt a forensic, diagnostic approach to each project, first understanding how the building is performing before prescribing changes. A key part of this will usually involve a measured survey and condition report. However, increasingly, building performance monitoring is also being deployed to better understand buildings, through thermal imaging, moisture monitoring through seasonal cycles, and occupant interviews to reveal how buildings are actually being used. This information can then be used to test assumptions and help prioritise interventions.
“We’ve learnt the hard way that you can’t just work off assumptions,” says David Pickles of the SPAB (Society for the Protection of Ancient Buildings) who works with heritage architects on technical guidance for buildings, “We had some horrific cases of interventions specified using theoretical models that completely failed because the building didn’t perform like the model thought it would. Now we are a big advocate of monitoring ahead of intervention, so at least you know what you are dealing with.”
This data-driven approach can help to reveal opportunities for intervention which might not otherwise have been considered. For example, a building with high thermal mass and good passive solar gain could require less insulation than first assumed, or a building with carefully designed natural ventilation might not need additional mechanical systems. On the other hand, a detailed investigation might reveal that the historic fabric of a building has already been severely compromised by previous alterations, and more extensive intervention would be justifiable.
Heritage architects also act as important intermediaries between a range of stakeholders, balancing the demands of building owners wanting to meet energy regulations, conservation officers concerned with heritage significance, planning authorities weighing up public benefit, and building control officers enforcing energy performance standards. Navigating this complex field requires not only technical acumen but also diplomatic skills, effective communication, and the ability to build consensus on complex trade-offs.
The professional landscape for heritage architects is in flux. The RIBA (Royal Institute of British Architects) has in recent years pushed sustainability higher in its competency frameworks, while organisations such as the IHBC (Institute of Historic Building Conservation) have developed technical guidance on climate change adaptation and mitigation. Such professional bodies are recognising that heritage practice is no longer just about preservation but must actively engage with environmental performance of the buildings in their care.
But heritage architects face significant pressures. Fee structures often do not adequately compensate for the additional time needed for sensitive retrofit work. The liability environment can also disincentivise innovation, particularly around novel or breathable insulation materials that have shorter performance track records. And there is a significant supply-and-demand issue: the volume of historic building stock that needs attention far outstrips the existing number of heritage specialists.
Some practices are starting to respond by building environmental expertise in-house, by hiring building physicists or energy consultants to work alongside conservation architects. Others are looking to form collaborative partnerships with engineering practices or research institutions. The most forward-thinking are even directly contributing to the evidence base, by monitoring completed projects to better understand performance in the long term and publishing findings to help the sector as a whole move forward.
The key message from the practice of good heritage architects is to avoid polarising positions. It is not about either insisting on a dogmatic “pure” historic building which must never be touched or grudgingly retrofitting old buildings with standard measures regardless of their heritage value. A better way forward is what could be described as “intelligent conservation” – evidence-based interventions that are sensitive to the cultural significance of buildings, proportional, and aligned with both environmental and cultural value.
This is neither an easy nor a simple endeavour. It requires skill, patience, expertise, and a willingness to live with some uncertainty. But if the complex question of retrofitting our historic building stock is to be solved, then it will require this sort of calibrated professional judgment. Heritage architects, at their best, demonstrate that conservation and sustainability need not be diametrically opposed: they are two sides of the same coin of responsible stewardship, both ultimately concerned with how to ensure buildings are fit for the future.
