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Research Case studies

Increasing energy efficiency and reducing the performance gap in buildings


Our work

Research undertaken by the Leeds Sustainability Institute (LSI) was fundamental to establishing the concept of the “performance gap” which is now ubiquitous in building energy efficiency policy. Our research has also led to changes to the Building Regulations and established building performance evaluation (BPE) as a major focus for research council and industry funding.

Our research has been used as evidence in Parliamentary Select Committees, APPGs and Green papers, and the Each Home Counts industry review. Our staff have also been seconded into Government Departments to share the knowledge and understanding of the issues we are discovering.

Perhaps the two greatest impacts our group has had are; 1) discovering the party wall thermal bypass, which, directly led to changes in the Building Regulations, and established cavity party wall insulation in the domestic retrofit policy (now a multi-million-pound insulation market) and 2) developing the “co heating” test, which has become an international CEN-standard methodology and is now used by other institutions as the reference test for validating other BPE methodologies and forms the basis for future research into validating building performance through the use of smart meters.

Our impact

In our 2005 review for the Office of the Deputy Prime Minister, we highlighted the risks involved with improving housing standards (Bell et. al., 2005), one of the first revelations of its kind ad upon which much research, policy changes and industrial practices have now been built.

Another evident example of the impact the LSI has had is that associated with our establishment of the electric co heating test to measure the whole house heat transfer coefficient (HTC). This uniquely provided a reliable empirical measurement of a building’s heat loss that could be compared to design standards.

Most eminent of the LSI’s early studies was the 2001 to 2008 Stamford Brook field trails (Wingfield et al., 2011), funded by the National Trust and the DCLG, which was the first study to measure, not only the extent of energy underperformance, but also identify the technological and process causes. This work is still relevant today, commonly being referenced by researchers and stakeholders in the field of BPE.

One of the most impactful findings from these studies is the thermal bypass in party wall cavities (Lowe et al. 2007), a hitherto unrecognised heat loss mechanism that is now incorporated into the Building Regulations and the Government’s building carbon calculation methodology which underpins Energy Performance Certificates (EPC) for over 18 million homes in the UK.

The notoriety gained from our research yielded opportunities to undertake additional field trials where similar observations corroborated tour early findings and it became clear that the “performance gap” between the as-built energy efficiency and the intended design values in new build homes was endemic. Among these field trails was the 2008 to 2012 Elm Tree Mews project, funded by the Joseph Rowntree Foundation, which identified how the performance gap may affect zero carbon buildings, renewable technologies and off site construction (Bell et al. 2010).

To build on the power of the performance gap concept observed in building fabric, we extended the scope of our research to investigate if the performance gap existed within services and renewable technologies in buildings, with for example, our EPSRC funded project, finding that heat pump efficiencies are regularly below stated levels (Stafford 2011).

The information from these and other LSI field studies was becoming particularly persuasive in industry and government and was fundamental to the evidence base of the Zero Carbon Hub reports, which informed the Government’s zero carbon homes policy and have persuaded house builders to accept the existence of the performance gap in their industry and to change their practices. The LSI’s evidence on the performance gap contributed to the Technology Strategy Board (TSB), now Innovate UK, setting up an £8million BPE Program for new homes which was based on the LSI’s co heating methodology as the standard test method.

The next step in the performance gap story, was to investigate if underperformance could be reduced or avoided.  The LSI undertook research on this and discovered that when advance low energy standards and practices are employed (e.g. Passivhaus), the performance gap can actually be minimised. This has significant implications for opportunities for improvement in the building industry and the accuracy of government energy modelling.

Having fundamentally changed the way that new homes are designed, modelled and built, the LSI next turned their attention to investigate if the performance gap also existed in the growing retrofit market in existing homes.  The Department for Energy and Climate Change (DECC) commissioned the LSI to investigate this in advance of their flagship ECO and Green Deal policies. In the resulting wide-ranging Leeds Core Cities Green Deal project (Glew et. al. 2017) it was confirmed that performance gap is a phenomenon that equally applies to retrofit.  More worryingly this work also lead to the discovery that unintended consequences, usually involving moisture problems, may be being retrofitted into millions of homes in the UK. 

This work has led to the LSI being commissioned by government and industry to undertake further research projects looking into how to reduce both the performance gap and unintended consequences by altering the process and individual materials used in retrofit.  For example, we have been commissioned based on our expertise to validate the effectiveness of other BPE technologies to assess how Smart Meters in over 25 million homes in the UK could replace the use of current EPC in evaluating retrofit success and tracking government policy.  We have also been asked to investigate the holistic impact of novel retrofit solutions for one of the government’s major retrofit problems; solid wall insulation.  Moreover, our work undertaken on hygothermal modelling of retrofits and their impacts on neighbours is among the first to be undertaken anywhere and is contributing to the emergence of a new research area in BPE.

Our research into retrofit has fed into the development of new PAS2035 standards which embraces “whole house thinking” via the Each Homes Counts review and the new Quality Mark for retrofits, which sets out guidelines to ensure that all future retrofits can avoid these problems. It is not clear the extent to which this may address the underlying causes of the problems and initial LSI research is revealing that socio-technical issues may also be playing a role in the delivery of retrofits that are not fit for purpose, suggesting more stringent standards may not solve the problem.

Next steps

The LSI will continues its strategic relationship with government by seconding its researchers, contributing to calls for evidence and participating in government funded research.  We will continue to consolidate our position as leaders in BPE field testing, energy and hygrothermal modelling by taking part in international and nation research projects with partners from government, industry and other academic instructions.

Specifically our capability to use of smart meter data coupled with our BPE expertise means we have been commissioned to validate all of the new smart meter BPE technologies being trialled by government to replace EPC.  This in addition to our modelling capabilities has also given us invitations to International Energy Annexes on maximising the potential for using in use monitoring data to replicate field trials as well as investigate the potential for energy storage as part of future smart buildings and cities.

In addition, we have identified wider areas of research to complement our existing research capabilities and specifically look into some of the underlying issues that we have uncovered, specifically in two areas;

  1. to investigate how socio-technical issues are affecting industry practice and householder energy use we are growing our behaviour change team. For example we currently have projects with power infrastructure organisations to understand how householders can be nudged to change how they consume energy. We also have government funded projects to investigate how to design messaging to encourage retrofit installers to take on good practice.
  2. to understand how large data sets can provide additional insights into BPE.  We have expanded our expertise in data science leading to us republishing a cleaned version of the Government’s publically available EPC database for almost 20 million homes in the UK. We are also taking part in the initial development of the UK’s first Smart Meter Research Portal, funded by the EPSRC, and we have already investigated what smart meter data for 18,000 homes can contribute to understand how effective government price caps will be, identifying that their calculation methodology is flawed and could lead to leaving fuel poor households worse off.

Research outputs

Plus Icon Key research papers
  1. Bell, M., Smith, M. and Miles-Shenton, D. (2005) Condensation risk – impact of improvements to Part L and Robust Details on Part C. Report Number 7 –Final report on project Field work. IN Oreszczyn, T. Mumovic, D, Davies, Ridley, I. Bell, M., Smith, M., Miles-Shenton, D. (2011) Condensation risk – impact of improvements to Part L and robust details on Part C: Final report: BD2414. Communities and Local Government, HMSO, London. [ISBN: 978 1 4098 2882 2 UK].  
  2. Lowe, R.J., Wingfield, J. Bell, M. and Bell, J.M. (2007). Evidence for heat losses via party wall cavities in masonry construction. Building Services Engineering Research and Technology, Vol 28 No. 2, pp.161-181.
  3. Wingfield, J., Bell, M., Miles-Shenton, D., South, T. and Lowe, R.J. (2011). Evaluating the impact of an enhanced energy performance standard on load-bearing masonry domestic construction: Understanding the gap between designed and real performance: lessons from Stamford Brook. Communities and Local Government, HMSO, London. [ISBN: 978 1 4098 2891 4].  
  4. A, Stafford and D, Lilley., (2012) Predicting In-situ Heat Pump Performance: An Investigation into a Single Ground-Source Heat Pump system in the context of 10 similar systems. Energy and Buildings.
  5. Johnston, D., and Miles-Shenton, D., and Farmer, D., (2015) Quantifying the domestic building fabric 'performance gap'. Building Services Engineering Research and Technology, 36 (5). 614 - 627
  6. Stafford, A and Johnston, D and Miles-Shenton, D and Farmer, D and Brooke-Peat, M and Gorse, C (2014) Adding value and meaning to coheating tests. Structural Survey, 32 (4). 331 - 342
  7. Johnston, D., Miles-Shenton D., Farmer, D., Brooke-Peat, M., (2015) Post Construction Thermal Testing: Some Recent Measurements, Engineering Sustainability, 168, (3), 131-139
  8. Johnston, D., Farmer, D., Brooke-Peat, M., Miles-Shenton, D., (2016), Bridging the Domestic Building Fabric Performance Gap, Building Research & Information, 44, (2), pp 147-159.
  9. Stafford, A and Johnston, D (2016) Estimating the Background Ventilation Rates in New-Build UK Dwellings – is n50/20 appropriate? Indoor and Built Environment, 26, (4), 502-513
  10. Gorse, C., Glew, D., Johnston, D., Fylan, F., Miles-Shenton, D., Smith, M., Brooke-Peat, M., Farmer, D., Stafford, A., Parker, J., Fletcher, M., and Thomas, F. (2017), Core cities Green Deal monitoring project – Leeds, prepared for the Department of Energy and Climate Change.
  11. Fylan, f., Glew, D., Smith, M., Johnston, D., Brooke-Peat, M., Miles-Shenton, D., Aloise-Young, P., Gorse, C., (2016), Reflection on Retrofit: Overcoming barriers to energy efficiency, Energy Research and Social Science, 21. pp. 190-198
  12. Farmer, D., Miles-Shenton, D., Johnston, D., (2016), Obtaining the heat loss coefficient of a dwelling using its heating system (integrated coheating), Energy and Buildings, 117, 1-10
  13. Glew, D., Miles-Shenton,, D., Smith, M., Gorse, G., (2017) Assessing the quality of retrofits in solid wall dwellings, 35 (5), 501-518
  14. Fletcher, F., Johnston, D., Glew, D., Parker, J., (2017), An empirical evaluation of temporal overheating in an assisted living Passivhaus dwelling in the UK, Buildings and Environment, 121, 106-118
  15. Alzetto, F., Farmer, D., Fitton, R., Hughes, T., Swan, W., (2018) Comparison of whole house heat loss test methods under controlled conditions in six distinct retrofit scenarios, Energy and Buildings, 168, 35-41
  16. Hardy, A., Glew, D., Gorse, G., (2018), Validating solid wall insulation retrofits with in-use data, Energy in Buildings, 165, 200-205
Plus Icon Building Regulations and policy impact
  1. NAO (2008) Programmes to reduce household energy consumption. Report By The Comptroller And Auditor General | HC 1164 Session 2007-2008 | 11 November 2008, The Impact case study (REF3b) Page 4 National Audit Office, LONDON: The Stationery Office.
  2. CLG (2009) Proposals for amending Part L and Part F of the Building Regulations – Consultation, Reference number: 08BD 05287, June 2009, London, Department for Communities and Local Government, ISBN: 978-1-4098-1532-7.
  3. PAC (2009) Programmes to reduce household energy consumption. Fifth Report of Session 2008–09 Report, together with formal minutes, oral and written evidence. House of Commons Public Accounts Committee, London: The Stationery Office Limited.
  4. CLG (2012) 2012 Consultation on changes to the Building Regulations in England: Section two - Part L (Conservation of fuel and power). January 2012 London, Department for Communities and Local Government, ISBN: 978-1-4098-3324-6,
  5. Zero Carbon Hub, (2014), Closing The Gap Between Design & As-Built Performance, End of Term Report,
  6. CIC, (2015), All Party Parliamentary Group for Excellence in the Built Environment Inquiry into the Quality of New Build Housing in England Fourth evidence session - Doing things differently.
Plus Icon Industry standards impact
  1. Johnston, D. Miles-Shenton, D. Wingfield, J. Farmer, D. And Bell, M. (2012) Whole House Heat Loss Test Method (Coheating). A report for the IEA Energy Conservation in Buildings and Community Systems Programme Annex 58: Reliable Building Energy Performance Characterisation Based on Full Scale Dynamic Measurement. Leeds, UK, Centre for the Built Environment, Leeds Metropolitan University
  2. Innovate UK, (2016), Building Performance Evaluation Programme: Findings from domestic projects; Making reality match design.
  3. Johnston, D., Siddall, M., (2016), The Building Fabric Thermal Performance of Passivhaus Dwellings—Does It Do What it Says on the Tin?, Sustainability, 8 (1), 97
Plus Icon Markets and consumers impact
  1. Bell, M., Wingfield, J., Miles-Shenton, D. and Seavers, J. (2010) Low Carbon Housing: Lessons from Elm Tree Mews. Joseph Rowntree Foundation, York. ISBN: 978-1-85935- 766-8.
  2. ARC, (2018), Eaves Insulator; Thermal insulation at wall plate/ceiling junction, V1.1 05.01.2018.

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