Retrofitting historic stock requires a pragmatic approach

As property professionals, we have a crucial role to play in reducing the impact of the historic built environment on the climate. However, this entails a variety of different pragmatic considerations.

Importantly, we need to think about the whole building when we are proposing sustainable retrofit, and consider building users as well.

A whole building approach advocates thinking about building retrofit in a joined-up, holistic and risk-based way.

This includes understanding how buildings of traditional construction and their occupants interact and perform to avoid negative unintended consequences. For example, slowing heat loss by improving air tightness resulting in reduced ventilation and a subsequent increase in moisture and humidity, and increased risk of damp and mould.

Before determining a course of action, building surveyors and conservation surveyors should consult documentation and guidance, and take into account context such as the age and fabric of the building, the client's objectives, and the way the building is being used. Determining what consents may be required for the proposed work is essential, which may include conservation approval in the case of designated buildings.

Measurement before and after works can establish the effectiveness of interventions where budget permits, while long-term planning can make the best use of limited resources; but it is also vital to ensure that those involved in the work at all stages are competent.

While these apply to properties of all ages, more specific guidance on heritage buildings can be found in publications by Historic England and Historic Environment Scotland, dealing with climate change risks and hazards and their impact.

Meanwhile, tools such as the Carbon Risk Real Estate Monitor (CRREM) can help us determine when assets are likely to become stranded – that is, when they fail to meet energy efficiency standards or market expectations and thus become obsolete – and inform interventions to avoid this.

There are a range of guides, frameworks and tools available, such as, for example, IHBC's retrofit guidance, while others may be more specific to particular building typologies.

Increased biodiversity could include features ranging from the introduction of bird boxes through to green roofs. Indeed, some countries such as Germany mandate the inclusion of green roofs when buildings undergo refurbishment.

This not only enhances biodiversity but also supports natural cooling, mitigating flooding and can improve local air quality. However, consideration should be given to aspects such as maintenance including ongoing costs, access, and health and safety.

The purpose of each measure will help determine how it should be installed. For example, what will the energy produced by a photovoltaic (PV) system be used for – heating, electricity, electric vehicle charging, a combination of these or something else?

If the intention is to use it for a heat pump, for example, the greatest energy demand is likely to be during the winter months. This may mean the angle for the PV array should maximise generation during the darker months, rather than optimising annual electricity production – an approach adopted, for example, by the Tudor manor Athelhampton House in Dorset, which has achieved net-zero carbon in terms of operational emissions.

But as well as client objectives, building users need to be considered as part of the design and specification: their behaviours and lifestyle, and the way that a building is operated will affect the emissions generated. A home, for example, will have a different energy use intensity, pattern of energy consumption, and energy needs compared with other typologies such as retail.

It is also worth being aware of recent case law such as Clipper Logistics Plc v Scottish Equitable Plc - 2022, unreported, County Court at Sheffield, 7 March. 

This case found that green clauses could only be added to leases on renewal where it was fair and reasonable for both parties.

Guidance on green leases is available from the Better Buildings Partnership and from the Chancery Lane Project, for both residential and commercial properties.

In England, around a fifth of domestic stock and around a third of non-domestic stock were constructed before 1919, demonstrating the long lives as well as resilience of such buildings, because their fabric tends to be more permeable.

Any interventions specified need to take this into account, to avoid negative unintended consequences. For instance, applying a modern waterproofing system to traditional fabric could inadvertently trap moisture inside the building or between building layers, resulting in damage.

Indeed, building professionals have noted a range of unintended consequences arising from some retrofits, including buildings of traditional construction that commonly have solid walls.

The Building Research Establishment report, Solid wall heat losses and the potential for energy saving, has identified 29 such consequences grouped into eight categories: 

• increased moisture levels
• airtightness and ventilation
• impact on aesthetics
• impact on asset value
• disturbance during installation
• impact on maintenance
• reduction in natural daylighting
• potential fire risk. 

Understanding potential pitfalls means we can design them out or mitigate them, and whole-building thinking will help with this; as can tools such as the Sustainable Traditional Buildings Alliance's Guidance Wheel, which highlights potential interactions between measures. 

Avoiding overcomplicated retrofits, interventions, measures or systems can also help prevent unintended consequences.

Modelling performance based on assumptions – as, for example, in the Reduced data Standard Assessment Procedure (RdSAP), which underpins domestic energy performance certificates (EPCs) – can provide a starting point. However, measurements in situ may identify better or worse performance.

Determining actual performance can be as straightforward as investigating actual energy usage and establishing whether this is reasonable. This may be established through benchmarking that is comparing building energy performance with a range that is typical for its typology and use. In buildings of traditional construction SAP is known to overestimate heating energy use, for instance, and may therefore suggest greater levels of intervention than actually required.

Measurements in situ can lead to different approaches, interventions and systems being adopted, to make a noticeable impact while avoiding unnecessary gains in embodied carbon. It is then useful to measure the building performance after retrofit to establish whether it is as expected or whether further adjustments are required.

This may involve grouping works together for cost efficiencies, such as limiting the number of times scaffolding is required, to reduce costs and disruption for occupants.

In some situations, small gains can be achieved by optimising the existing building by improving its condition, reducing draughts, installing low-energy lighting, and taking soft retrofit measures such as thermally lined curtains and shutters.

This can reduce the necessity for further works or interventions, thus avoiding unnecessary embodied carbon and waste.

Of course, some interventions may not result in noticeable changes to the EPC rating and are not likely to achieve net-zero carbon by themselves. However, they may improve comfort or climate change resilience, for instance.

Interventions could be considered as part of planned maintenance or works, during which surveyors can determine whether enabling works for further interventions can be carried out, to help clients save money over the longer term.

Taking a long-term view also extends to thinking about the maintenance demands and lifespans of the measures and systems being specified.

Considerations regarding material and product sourcing should not only take account of their performance and appropriateness for the building but also their environmental footprint including where they are sourced from and how they are transported, maintainability and so on. Could systems or products be sourced locally, for instance, and create social value?

If systems are not commissioned correctly, they may not operate as intended, increasing frustration, discomfort and operational costs for building users, deterring other people from specifying such measures in the future.

With competent contractors and consultants needed to carry out projects, organisations such as Grosvenor have been supporting supply chains to meet sustainability standards, while some contractors have seen the business opportunity in upskilling their staff. However, the training can be costly and time-consuming. 

Nevertheless, training opportunities for the supply chain can contribute to social value and help enable integration between parties along the chain, collaboration and sharing knowledge.

As surveyors and built environment professionals we are well placed to consider how to embed sustainability practically into the work we undertake. Using our knowledge and understanding of the nature and performance of buildings, we may identify opportunities to innovate – which can extend beyond measures and systems to matters such as finance, contract agreements, supply chains and more.

To explore how some of these sustainability considerations play out in practice, the next article will show how they informed the National Trust's recent conservation work on both a domestic and non-domestic building.