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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) has been fundamental in establishing the concept of the “performance gap” which is now ubiquitous in building energy efficiency policy. Our research has not only led to changes to Part L of the Building Regulations for England and Wales, but it has also established building performance evaluation (BPE) as a major focus for research council, government 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 that we are discovering.

The two greatest impacts our group has had are; 1) providing empirical evidence that the party wall bypasss could be responsible for a significant amount of heat loss and was contributing to the discrepancy between the predicted and measured heat loss of new dwellings, often termed the building fabric thermal ‘performance gap’.  This work directly led to changes to Part L of the Building Regulations, and established cavity party wall insulation in UK domestic retrofit policy (potentially a multi-million-pound insulation market) and 2) developing the electric “co heating” test, which is in the process of being developed into an international CEN-standard and has been used by other institutions (both in the UK and abroad) as the reference test for assessing the aggregate performance of the building fabric in both new and existing dwellings. The electric coheating test has also been used to validate other building fabric thermal performance methodologies and is forming the basis of future research into validating building fabric thermal performance through the use of smart meter data.

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 and 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 development and application of the electric coheating test method to measure the whole house heat transfer coefficient (HTC) of a building. This method uniquely provided a reliable empirical in situ measurement of a building’s heat loss that could be compared to design aspirations and calculations.

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

One of the most impactful findings from these studies was providing the empirical evidence base associated with the cavity party wall thermal bypass (Lowe et al., 2007), a heat loss mechanism that is now incorporated into Part L of the Building Regulations in England and Wales. It is also incorporated within the Government’s building carbon calculation methodology, which underpins the Energy Performance Certificates (EPCs) of over 18 million dwellings in the UK.

The attention gained from our early research led onto further field trials where similar observations corroborated and reinforced our early findings associated with the building fabric thermal performance gap. This work not only suggested that the performance gap issues were endemic in new build housing in the UK, but also confirmed that they extended from the fabric and included building services systems and the occupants.

Amongst 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 and low carbon buildings (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, of which LSI staff were members. These reports were instrumental in informing 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 also contributed to the development of the £8millionTechnology Strategy Board, now Innovate UK, Building Performance Evaluation Programme. The LSI undertook 25% of all testing under this program and the LSI’s electric coheating testing methodology, formed an integral part of all the domestic projects funded under this programme.

As part of this programme, the LSI undertook research on a number of dwellings that had been constructed to advanced low energy standards, such as the Passivhaus Standard, and collected empirical evidence that indicated that the building fabric thermal performance gap could be reduced to a negligible level in such dwellings (see Johnston & Siddall, 2016; Johnston, Miles-Shenton and Farmer, 2015; Johnston et al., 2014)); . This finding is the first of its kind and has significant implications for the new house building industry, both nationally and abroad.

Having questioned 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 (Gorse et al., 2017), the empirical data confirmed that performance gap is a phenomenon that equally applies to retrofit. This work also led to the discovery that unintended consequences, usually involving moisture problems, may be being inadvertently being retrofitted and ‘locked-in’ to millions of homes in the UK. 

This work has led to the LSI being commissioned by government and industry to undertake further research projects aimed at reducing both the building fabric thermal performance gap and unintended consequences, by altering the process and individual materials used in retrofit.  For example, we have been commissioned to validate the effectiveness of a range of novel BPE technologies that are being developed to measure the aggregate HTC of occupied dwellings in situ using smart meter data as well as 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 amongst the first to be undertaken within this area, and as such, is contributing to the emergence of a new research area in BPE.

Our research into retrofit has also fed into the development of the new PAS2035 standards which embraces “whole house thinking” via the Each Homes Counts review and the new Quality Mark for retrofits. These guidelines attempt to ensure that all future retrofits can avoid unintended consequences and the performance gap. 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 significant role in the delivery of retrofits that are not fit for purpose. This suggests that more stringent standards may not solve the problem.

Next steps

The LSI will continue 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 in situ 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 smart meter data, coupled with our BPE expertise, means that we have been commissioned to validate all of the new smart meter BPE technologies being trialled by government to measure the aggregate HTC of existing occupied dwellings in the field.  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 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.  This builds on work already undertaken to investigated what smart meter data for 18,000 homes can contribute to understanding how effective government price caps will be, and 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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