Man laying insulation in loft.
Traditional buildings deal with internally generated moisture loads through natural air leakage but also through the moisture buffering capacity of certain insulation materials. © NTPL/Alexander Caminada
Traditional buildings deal with internally generated moisture loads through natural air leakage but also through the moisture buffering capacity of certain insulation materials. © NTPL/Alexander Caminada

Filling in the Retrofit Gaps

A new report highlights research into the energy efficiency and performance of traditional buildings and the gaps that still exist.

To achieve the UK Government’s target to bring all greenhouse gas emissions to net zero by 2050, many historic and traditionally constructed buildings will need to be upgraded to improve their performance and reduce their carbon footprint.

There are nearly 5 million houses of traditional construction in England, built mostly before 1919, accounting for around 21 per cent of the housing stock. These include houses that are designated as listed buildings, as well as 2.8 million households that are in conservation areas. These houses are generally built with solid walls, rather than cavity walls, or are of timber-frame construction.

Assumptions about the poor energy performance of older buildings are often not borne out by the evidence. For example, research carried out by Historic England showed that the measured performance of solid brick walls was a third better than the performance predicted by energy-performance models. But that doesn’t mean that there isn’t scope for improvement. However, we want to see the retrofit of historic buildings delivering improved energy performance in a sustainable way that conserves their values and significance, without harming building fabric and the health of the occupants or risking other unintended consequences.

Tackling these issues is a key part of Historic England’s technical conservation research programme and will help to ensure that historic buildings retain their character and remain viable and useful, now and into the future. Historic buildings are durable, repairable and adaptable, which is why they have survived over so many generations. They are also culturally, socially, economically and environmentally valuable to society.

Our research is aimed at informing best practice and reducing risks from maladaptation. We work with a range of researchers from universities to historic environment specialists.

This year we commissioned the Sustainable Traditional Buildings Alliance (STBA) to identify where new research is still required, and in June we published Performance and Energy Efficiency of Traditional Buildings: Gap Analysis, Update 2020.

Background to the research

The STBA was launched in 2012 to act as a forum for organisations interested in trying to better understand the performance of traditional buildings as well as improving research, policy, training, practice and guidance.
In that same year, STBA was funded by Historic England and the Construction Industry Training Board Construction Skills to produce Performance and Energy Efficiency of Traditional Buildings: Gap Analysis which mapped the current state of knowledge of this area among institutions and professionals.

The STBA study revealed that there was very limited published evidence on the performance of traditional buildings. There were significant gaps in understanding how buildings perform and how they behave when changed, and critically a lack of accurate data.

The study also encouraged debate and further investigation into retrofitting traditional buildings. It helped to shape thinking on areas requiring new or further research, training and skills development, and promoting best practice.

In 2012, STBA was also commissioned by the Department of Energy and Climate Change to undertake a similar but more in-depth exercise. This commission arose from concerns about the application of certain Green Deal retrofit measures to traditional buildings, including the possibility that they might fail to achieve financial and energy payback, the risk of harm to building fabric and human health, as well as missed opportunities for the improvement of traditional building performance. This report, Responsible Retrofit for Traditional Buildings, focused on identifying significant gaps in research as well as guidance.

The 2020 Gap Analysis

The updated analysis takes stock of the considerable amount of research that has been undertaken since the initial report. Significant research on traditional buildings has been carried out since 2012 by Historic England, Historic Environment Scotland, the Society for the Protection of Ancient Buildings, STBA and others, including studies into thermal performance which led to the Government changing the default U-value of sold brick walls from 2.1 W/m2K to 1.7. Yet, while we now have a much better understanding of building performance and the risks of retrofit, substantial gaps remain.

The updated analysis explores 13 topics that have an impact on the sustainable retrofit of traditional buildings including ventilation, thermal comfort, energy and thermal performance, and occupant interactions. For each topic the issues and existing research are summarised, and the gaps identified where research is needed to inform best practice.

One area where more research is needed is the impact of the retrofit on the health and well-being of occupants. For example, we know that excessively cold and draughty buildings can affect people’s health, but insulating too tightly without considering adequate ventilation can result in poor indoor air quality, damp and mould – all of which can adversely affect health and wellbeing. We need a better understanding about the impact of retrofit on air quality.

Another area of interest is moisture. Despite much research since 2012 into the moisture performance of retrofitted buildings, there is still a lack of long-term monitoring of the effects on moisture accumulation. This is essential to fully understand the risks to historic fabric and to the health of the occupants as a result of retrofit measures. The establishment of the UK Centre for Moisture in Buildings is a step in the right direction.

It is widely recognised that basic repair and maintenance to traditional buildings can significantly improve their heat and moisture behaviour, yet there is no research to back this up. Therefore research is needed to gather data on energy use and hygrothermal performance before and after basic repairs.

Other areas highlighted where further research is needed include:

  • impact on character and significance
  • energy performance data
  • heating and fuel sources
  • overheating and cooling
  • embodied carbon and the circular economy
  • public and political understanding
  • professional understanding of the cost of retrofit measures
  • properties of building materials, and technical specifications

 The report also provides an overview of 15 current research programmes in universities around the country. An appendix provides an extensive literature review of key research and some significant guidance published since 2012 to the present.

Our research and guidance

In recent years, Historic England’s research programme has helped to inform our comprehensive guidance on improving the thermal performance of historic and traditionally constructed buildings.

Historic and traditionally constructed buildings are very diverse. There are no ‘one-size-fits-all’ energy-performance solutions.

Fabric improvements are only part of the solution and in many cases an exclusive focus on ‘fabric first’ risks harming fabric and people’s health and failing to achieve the hoped-for benefits. We believe that a holistic – or ‘whole building’ – approach, that takes into account the building’s context, condition, occupant behaviour, and services, as well as wider issues such as energy supply, is essential to achieve effective and sustainable improvements in building performance whilst maintaining significance, reducing greenhouse gas emissions and avoiding unintended consequences, such as damp. This is explained in our guidance publication Energy Efficiency and Historic Buildings: How to Improve Energy Efficiency (2018).

Our current research is concentrating on this whole building approach. Our projects include an investigation into the thermal performance of traditional buildings; risks from moisture accumulation as a result of retrofit; hygrothermal behaviour of building fabric; and assessing carbon in the built historic environment.

You can expect more reports on topics such as low-energy approaches to thermal comfort, case studies on a retrofitted Victorian terraced house, and the hygrothermal performance of walls, to be published in the near future, so look out for more on these soon.

The findings of the Gap Analysis report will help shape Historic England’s own climate change adaptation research agenda, as well as that of the wider sector.

About the author

Jessica Hope

Publications and Outreach Coordinator with Historic England

Jessica joined Historic England in early 2020 and works on producing and promoting new guidance publications and research reports in the National Specialist Services Department.

Further information

Sustainable Traditional Buildings Alliance 2020: Performance and energy efficiency of traditional buildings: Gap Analysis, Update 2020, Research Report Series 210/2020.

Sustainable Traditional Buildings Alliance 2012: Performance and Energy Efficiency of Traditional Buildings – Gap Analysis Study

Griffiths, N and May, N 2015: Planning Responsible Retrofit of Traditional Buildings

Sustainable Traditional Buildings Alliance 2012: Responsible Retrofit of Traditional Buildings

Historic England’s advice on energy efficiency and historic buildings

Historic England’s current research on energy efficiency

Historic England’s research on Carbon in the Historic Environment

Historic England 2020 Written evidence to the Parliamentary Environmental Audit Committee EEH0104 – Energy Efficiency of Existing Homes inquiry

Webinar on ‘Climate change adaptation: Whole house approach to retrofit’, September 2020

Historic England 2014 Practical Building Conservation: Building Environment, Ashgate Publishing: Farnham 

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