Heat flux sensor used to measure the transmittance of heat through building elements
Heat flux sensor used to measure the transmittance of heat through building elements © Iain McCaig / Historic England
Heat flux sensor used to measure the transmittance of heat through building elements © Iain McCaig / Historic England

Energy Efficiency

Our research focuses on understanding and improving the energy performance of historic buildings and the effects of measures to increase energy efficiency. This will help them remain viable and useful, now and in the future.

As highlighted in our Heritage Counts report  the built historic environment has a vital role to play in the journey towards a low carbon future.

There are numerous incentives for carrying out improvements:

  • mitigating climate change
  • maintaining energy security
  • reducing energy costs and tackling fuel poverty
  • increasing comfort
  • complying with legislation

Unfortunately, unsuitable improvements may not deliver the savings predicted, and can harm the building and the health and well-being of its occupants. This aim of this research topic is to contribute to an evidence base that will enable better-informed decisions to be made about improving the energy and carbon performance of the historic built environment.

Overview of research on the sustainable retrofit of pre-1919 buildings

The ‘Performance and Energy Efficiency of Traditional Buildings: Gap Analysis Update 2020’ report, commissioned by Historic England from the Sustainable Traditional Buildings Alliance, explores 13 specific subject areas that have an impact on the sustainable retrofit of pre-1919 traditional buildings:

  • Health
  • Ventilation
  • Thermal comfort
  • Character and significance
  • Moisture performance
  • Energy performance
  • Embodied carbon
  • Occupant interactions
  • Public and political understanding
  • Repair, maintenance and enabling works
  • Professional understanding
  • Costs of retrofit measures
  • Material properties and technical specifications

A synopsis is provided for each area that defines its strategic importance and analyses the existing research that underpins current knowledge.

The report looks at the gaps where future research might be considered to help inform best practice, reduce risks and potential damage to both building fabric and the health of the occupants. Further research is explored by means of an overview of fifteen current academic research programmes.

The study is supported by a non- qualitative literature review covering key research and some significant guidance published since 2012 to the present day.

It builds on two previous studies: ‘Performance and Energy Efficiency of Traditional Buildings: Gap Analysis Study (English Heritage and CITB 2012) and the ‘Responsible Retrofit for Traditional Buildings’ (STBA 2012).

Participants: Historic England and Sustainable Traditional Buildings Alliance (STBA)
Read the research report: Performance and Energy Efficiency of Traditional Buildings: Gap Analysis Update 2020 

Thermal performance of traditional buildings

Research into the thermal performance of brick walls

Two studies have been carried out that focus on the thermal performance of solid brick walls. The aim the project was to quantify thermal transmission in terms of U-values by measurement in situ and complementary laboratory investigations.

Partners: Glasgow Caledonian University

Read the research report: Thermal performance of traditional brick walls

113 New Bolsover: Whole house thermal performance assessment

The aim of this project is to understand better the thermal performance of the roof, walls, floors and windows of a traditional dwelling, and the effectiveness of fabric improvements in reducing energy use and carbon emissions. The thermal performance of a two storey, end of terrace house in New Bolsover, Derbyshire was assessed before and after improvements carried out in 2011 using measured U-values and a co-heating test, and the results compared with calculated values. The effectiveness of the measures was evaluated using the SAP model. In addition, the cost efficiency of improvements was assessed.

Participants: Historic England's Building Conservation and Geospatial Survey Team, Glasgow Caledonian University, Bolsover District Council

Read the research report:
A Retrofit of a Victorian terrace house in New Bolsover: A whole house thermal performance assessment

External wall insulation in traditional buildings: Case studies of three large-scale projects in the North of England

Research was commissioned into three large-scale external wall insulation projects in the North of England. This focussed on a range of issues including methods of funding, pre-installation assessments, selection of materials and systems, design, specification, procurement and implementation, and highlighted factors affecting the quality of work. In addition, the heritage impact of the work was assessed, and the perceptions of stakeholders, including building occupants, were reviewed.

Participants: Historic England’s Building Conservation and Geospatial Survey Team, NDM Heath Ltd

Read the research report: External Wall Insulation in traditional Buildings

Research into the thermal performance of traditional windows

Historic England commissioned research to investigate the thermal performance of traditional timber sash windows and metal windows. Thermal transmission in terms of u-values was measured, and heat losses through air infiltratration draughts and thermal bridging were assessed. The work presented in the research reports quantifies the effectiveness of relatively simple measures to improve the thermal performance of windows by draught-proofing, and using blinds, curtains, shutters and secondary glazing.

Partners: Historic Scotland (now Historic Environment Scotland) & Glasgow Caledonian University

Read the research reports:
Research into the thermal performance of traditional windows: Timber sash windows

Improving the thermal performance of traditional metal-framed windows

The Engine House, Swindon: Thermal performance of energy efficiency improvements to timber windows

Tests have been carried out at Historic England’s headquarters in Swindon to compare three proprietary retrofit systems for improving the thermal performance of traditional timber windows. To assess their performance, U-values of glazing were measured in situ before and after the systems were installed. The results showed that all three systems reduced heat loss by more than 50%. The impact of each system on heritage values, and the operation and maintenance of the windows was also considered.

Participants: Historic England's Building Conservation and Geospatial Survey Team.

Read the research reports
The Engine House, Swindon: Thermal performance of energy efficiency improvements to timber windows

The SPAB Research U-Value Report

Moisture accumulation in building fabric due to energy efficiency measures

A programme of complimentary laboratory and site-based projects is underway to understand better the risks of condensation and moisture accumulation in building fabric due to retrofitted energy efficiency measures.

113 New Bolsover: Hygrothermal behaviour of internally insulated brick walls

The aim of this project is to monitor and compare the long-term effects of internal wall insulation (IWI) on the hygrothermal (moisture and heat) behaviour of solid brick walls in a Victorian end-of-terrace house in New Bolsover, Derbyshire. Two IWI systems have been installed, one ‘vapour diffusion closed ‘ (PIR), the other ‘vapour diffusion open’ (wood fibre). Temperature and moisture sensors have been installed at the interface between the insulation and the wall in XX locations . These are continuously monitored, along with the temperature and humidity of the interior of the house.

Participants: Historic England's Building Conservation and Geospatial Survey Team, Glasgow Caledonian University, Ridout Associates & Bolsover District Council.

Shrewsbury Flaxmill Maltings: Hygrothermal behaviour of internally insulated brick walls

This project is investigating the ways that both insulated and uninsulated solid brick walls respond to internal and external environmental loads. Two systems of internal wall insulation have been installed, as described above, in part of an 18th industrial building which is being heated and humidified to replicate occupation. Temperature and moisture sensors have been installed at the interface between the insulation and the walls. In addition, moisture sensors have been placed at intervals within the thickness of the wall. These are continuously monitored, along with the internal climate. Outside, a weather station monitors meteorological conditions, including solar radiation, and vertical rain gauges on the facades record wind driven rain.

Participants: Historic England's Building Conservation and Geospatial Survey Team, Glasgow Caledonian University & Ridout Associates

Laboratory-based investigation: Hygrothermal behaviour of internally insulated brick walls

The aim of this project is to monitor and compare the effects of different IWI systems on the hygrothermal behaviour of sample brick walls when subjected to ‘internal’ and ‘external’ environmental loads in a climate chamber. The data obtained will be used to assess the risk of moisture accumulation, and cross-validate data gathered in site-based monitoring. The project will also measure the effects of moisture on the thermal resistance of sample walls.

Participants: Historic England's Building Conservation and Geospatial Survey Team & Glasgow Caledonian University

Hygrothermal behaviour of roof spaces

This project is investigating the behaviour of heat, moisture and air in a range of traditional pitched slate and tile roofs under the influence of internal and external environmental loads. Up to five roofs, with and without underlay and with varying amounts of insulation either at ceiling level will be continuously monitored. Internal parameters include temperature and relative humidity above and below insulation and below ceiling, air velocity at high and low level, and surface temperatures of roof coverings and underlay. Timber moisture content is also being assessed. Externally, weather stations record meteorological data. The aim is to understand better the factors affecting the risk of condensation and moisture accumulation, and to evaluate the effectiveness of ventilation in managing the condensation risk.

Read more about the results of this research:
Condensation in historic roofs - article in the Building Conservation Directory, published by Cathedral Communications in January 2018.

Participants: Ridout Associates, Arboreal Architecture, building owners.

Hygrothermal behaviour of suspended timber ground floors

This project is investigating the behaviour of heat, moisture and air in sub-floor voids to assess the risk of moisture accumulation when insulation is provided at floor level. The effectiveness of ventilation in maintaining timber moisture contents at safe levels is also being appraised. Internal and external environmental parameters are being continuously monitored.

Participants: Historic England's Building Conservation and Geospatial Survey Team, Ridout Associates, building owners.

Numerical modelling of hygrothermal behaviour of building fabric

A programme of research to investigate factors affecting the accuracy of hygrothermal modelling, and its usefulness in assessing risks of moisture accumulation in walls due to retrofitted insulation.

See latest research article on Simulation Models and Energy Efficiency in Historic Buildings

Shrewsbury Flaxmill Maltings: Hygrothermal Modelling

Heat and moisture transport through brick walls at Shrewsbury Flaxmill Matlings were modelled using WUFI Pro 5 software. The aim of the study was to simulate the hygrothermal behaviour of the original construction and predict the impact of adding different types of internal wall insulation. Thirty-year simulations were carried out using climate data from a nearby location and measured material properties of a sample brick from the Flax Mill. Simulations were also run using material properties from the WUFI database. Different insulation systems were modelled including mineral wool, PIR and wood fibre. The results indicated that predictions are subject to high levels of uncertainty if measured material properties are not available, and where boundary conditions such as absorption of driving rain are unknown. The hygothermal behaviour of walls at the Flax Mill is currently being monitored. These measurements will be used to validate predictions and ‘calibrate’ the model.

Participants: Glasgow Caledonian University

Read the research report: Hygrothermal modelling of Shrewsbury Flaxmill Maltings

Sensitivity analysis of numerical modelling using WUFI Pro 5

Software applications (such as WUFI ®) that simulate hygrothermal behaviour of buildings and components are often used to assess the risk of moisture problems, for example where additional insulation is proposed. However, doubts about construction, material properties, internal environment, occupant behaviour and external climate lead to uncertainty in the output of simulations. The aim of this project is to investigate how uncertainty can be apportioned to various input data and identify the input fields that have the most significant impact on the accuracy of results.

Participants: Glasgow Caledonian University

113 New Bolsover: Hygrothermal Modelling

This builds on the two previous projects, described above, and has similar objectives: to validate the model and understand better the factors affecting the accuracy of predictions. The hygrothermal behaviour of internally insulated walls at 113 New Bolsover is being simulated using WUFI Pro software. The results will be compared with data measured on site over the past five years.

Participants: Glasgow Caledonian University

'Whole building' approach to energy and carbon savings in historic buildings

Analysis of energy saving measures in four solid-walled houses in Reading

An in-depth ‘whole building’ analysis of energy use has been carried out in four traditionally built houses in Reading, Berks. The results have been used to devise bespoke packages of measures to reduce energy use and carbon emissions. These were then assessed in terms of their effectiveness and cost-efficiency. A particular aim of the project has been to understand better the costs and benefits of solid wall insulation in relation to other energy and carbon saving measures. The project demonstrates the benefits of a ‘whole building’ approach, and shows how the economics of specific energy and carbon-saving measures vary from one household to another.

Participants: Parity Projects & Reading Borough Council

Read the research report: Reducing energy use in traditional dwellings: Analysis of four solid wall houses in Reading

The sustainable use of energy in traditional dwellings: Legislation, policy and decision making

Local authorities are responsible for implementing a diverse range of legislation, policies and guidance relating to sustainable development, fuel poverty, housing standards and carbon reduction. These all have impacts on the historic environment. But unless there is adequate inter-departmental understanding and coordination of the many overlapping (and sometimes conflicting) requirements, there is a risk that one agenda will be undermined by another. The consequences of this include harm to heritage assets and failure to meet legislative and policy objectives in full.

The aims of this project were to a) review current legislation, policy and guidance, and understand better the points of convergence and conflict; b) consider ways that local authorities can increase understanding between departments and stakeholders, and develop more integrated and better informed approaches to policy and decision making.

Participants: Centre for Sustainable Energy, Bristol

Read the research report: The Sustainable use of energy in traditional dwellings

Energy Performance Certificates (EPCs) and the Whole House Approach: A Scoping Study

Energy Performance Certificates (EPCs) were introduced by the Government as a bench marking standard to drive energy efficiency improvements. Historic England and the National Trust commissioned the Sustainable Traditional Buildings Alliance (STBA) to investigate issues, constraints and opportunities in applying this approach to older buildings.

The study explored ways in which EPCs could be better aligned with the ‘whole house approach’ to improving the energy performance of traditionally constructed dwellings, as developed by the STBA and recommended in the Government's Each Home Counts.  

You can download our report from our research reports database. The report outlines short term opportunities as well as potential future research to inform change.

Webinar on climate change adaptation and whole house approach to retrofit

View the 2020 webinar. Old buildings are very variable and there is no 'one-size-fits-all' solution to retrofit for traditional buildings. The 'whole house' approach considers the interrelationship between the occupants, the building fabric and the services of individual buildings. It then aims to find bespoke balanced solutions that save energy, sustain heritage significance and maintain a healthy indoor environment whilst managing the risks of unintended consequences.

The SPAB building performance survey 2011 - 2019

The SPAB's Building Performance Survey, was supported by Historic England. The project assessed the performance of a number of traditional buildings both before and after refurbishment designed to improve energy efficiency. Early phases of the project focussed on quantifying the thermal performance of a range of traditional wall constructions, including stone, brick and cob, by measuring their thermal transmission in situ. Measurements were carried out before and after refurbishment, and the effects of the energy efficiency measures on comfort and indoor air quality were also assessed. The last phase of the project looked into the long-term effects of adding insulation on the behaviour of interstitial moisture in walls.

Partners: The Society for the Protection of Ancient Buildings (SPAB), ArchiMetrics, Caroline Rye, Diane Hubbard, building owners

The full set of the 11 research reports is available on SPAB’s web site and also in our research reports database.

SPAB’s Energy Efficiency and Old Buildings: Principles and Priorities is drawn from the research.

Contact for all above projects: [email protected]

Carbon in the built historic environment

An important strand of our energy efficiency research is focused on embodied carbon.

In 2019, Historic England commissioned a scoping study on behalf of the Historic Environment Forum, from Carrig Conservation International to assess the ‘whole life’ carbon of historic buildings.

Buildings contribute to global warming over their whole lives: when we build, maintain, use and demolish or re-purpose them. However, the focus of carbon reduction strategies to date, has largely concentrated on emissions that occur when buildings are used – known as operational emissions. Meanwhile the carbon emitted during construction, maintenance and demolition or re-use – known as the embodied carbon emissions of buildings – remain largely neglected. A whole building approach measures carbon emitted at all stage of a building’s lifespan and demonstrates the importance of embodied carbon emissions.

The Carrig study uses a whole life approach to estimate carbon emissions associated with two completed historic building refurbishment and retrofit projects – one in the East Midlands and one in London. Using standard models and software applied to actual data (emissions before and after refurbishment), the life cycle carbon emissions were estimated for a 60-year period and also compared to equivalent new buildings.

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