New recommendations for housebuilders published based on unique new university research

The £3 million Demonstration of Energy Efficiency Potential (DEEP) project was commissioned by the Government’s Department for Energy Security and Net Zero. Investigating the retrofit (making energy efficiency improvements) of solid walled homes, it is one of the largest research studies of its kind to have ever been attempted in the UK. 

The research was carried out by the Leeds Sustainability Institute (LSI) at Leeds Beckett University in collaboration with the University of Salford and Loughborough University.  

The research found that insulating the UK’s eight million solid walled homes has the potential to cut energy bills by 30 per cent in some homes, and is essential to achieve domestic energy efficiency targets. Although solid wall insulation is expensive and tricky to install safely and effectively, the team found that there are many benefits to homes. These include: being cheaper to run, feeling warmer in winter and cooler in summer, having better air quality, and having less chance of condensation occurring. 

Professor David Glew, Director of the LSI at Leeds Beckett University, said: “Our research is done in real homes - so we understand how buildings perform in the real world, not just in labs and models. Solid walled homes are among the least energy efficient – occupants are more likely to be in fuel poverty, and condensation, damp and mould problems can be common.  

“Solid walled homes tend to have EPCs lower than Band C – the Government’s Clean Growth Strategy aims for as many homes as possible to attain an EPC rating of Band C by 2035. Our research found that insulating the solid walls of a home can achieve EPC Band C and could save up to 30 per cent per year for some homes on their energy bills. It was by far the single most effective retrofit measure for solid walled homes - other types of retrofit often don’t achieve the required improvement – and so will be essential for tackling fuel poverty.  

“At the moment, only 7%* of all retrofits taking place under the Energy Company Obligation (ECO) - the Government’s fuel poverty policy - are delivering solid wall insulation, since they are so costly and difficult to install. So, we hope this research can help shine a light on how important solid wall insulation is for the nation.” 

This new research measured how much the energy efficiency of the homes was improved by adding insulation and compared this with the predictions made by the homes’ EPCs. The study found that substantial improvements could be achieved. EPCs overestimated the heat loss measured in the project’s case study homes by an average of 42% - and were more accurate when measured data was used, for example through airtightness tests.  

EPCs currently use estimated or default values for these heat losses – based on information such as the age of the home. A key recommendation from the research is therefore to update and improve the range of input and default data that EPC assessors can use to improve accuracy. 

The project compared different methods of retrofitting solid walled homes in England– installing a range of insulation and energy efficiency measures in addition to solid wall insulation, including: loft insulation, floor insulation, draughtproofing, and installing new windows and doors.  

Predictions based on the project’s case study homes suggest fuel bill savings of between 11 and 29% for solid wall insulation alone - depending on the condition of the wall and how much external wall is insulated. When combined with other retrofit improvements, savings were modelled to be as high as 33% off annual bills.  

The researchers recommend using a ‘whole-house approach’ to retrofitting – rather than installing individual ‘piecemeal’ measures at different times.  

Professor Glew explained: “It is important that we insulate as many solid walled homes as possible, but also that we take great care when we do so - and the whole house approach is one way to achieve this. Although it is more expensive to deliver, it can bring significant benefits to households. 

“This is the first time that research has compared the impact of taking a whole house approach to insulation measures to the cumulative impact of piecemeal retrofits added over time. What we found was that piecemeal work can result in homes having higher risks of condensation at discontinuities – or gaps in the insulation layer - whereas the whole house approach reduces the likelihood of this happening. Retrofit can also reduce the risk of overheating, especially when the whole house approach includes ventilation and shading, to make our homes ready for future hotter summers.”

The LSI is a unique research group of building performance researchers based at Leeds Beckett University. They are among the top research teams carrying out scientific field trials in the UK, to show how buildings perform in the real world - not just in labs or models. 

Leeds Beckett is long established as a home for pioneering research into energy in homes. The co-heating test, which was characterised by LBU, measures the energy efficiency of buildings, and is now a global standard used worldwide. LSI research previously led to a change in building regulations which means all party walls in new homes in the UK now have to be insulated - resulting in hundreds of thousands of tonnes of CO2 being saved as a result of Leeds Beckett University research. It is hoped that this new research may have similar implications and result in improvements to retrofit policy and regulations.