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Investigating the retrofit of solid walled homes, the £3 million Demonstration of Energy Efficiency Potential (DEEP) project is one of the largest research studies of its kind to have ever been attempted in the UK.
Poorly insulated homes cost the environment and householders. The government wants to see every home possible to achieve a Band C EPC rating by 2035.
Just 40% achieves it now. Retrofitting energy improvements to the eight million solid wall homes in the UK would have a huge impact, but this can be tricky to do safely and effectively.
Solid walled homes were often built before modern building regulations were introduced and tend to be the least energy efficient, with the lowest EPC ratings. Occupants are more likely to be in fuel poverty - and condensation, damp and mould problems can be common.
Finding the right retrofit approach could bring many benefits. It can save fuel (and bills), make homes warmer in winter and cooler in summer, and it can reduce the chance of damp and condensation occurring.
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 of solid walled homes, it is one of the largest research studies of its kind to have ever been attempted in the UK.
The project addressed these five research questions:
Working in 14 real homes in England, the research team delivered 41 different fabric retrofits using multiple measures. They undertook before and after modelling and testing of every retrofit to pinpoint the improvement from each specific measure - and identify if there were any changes in moisture and overheating risks that occurred in the homes.
The team also tested the effectiveness of PAS2035 - the latest retrofit standard which advocates for a whole house approach to retrofitting. 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.
They installed the retrofits using traditional methods, carrying out performance tests and risk assessments. The team then upgraded the retrofits to the new standard, redoing the tests and models and comparing the difference.
The research study provides a thorough assessment and comparison of different methods of retrofitting solid walled homes - including solid wall insulation, loft insulation, floor insulation, draughtproofing, and new windows and doors. It also investigated the differences between piecemeal traditional retrofits carried out in stages, and the whole house approach - and how risks can be reduced when carrying out the work.
The researchers looked at three different ways of predicting energy efficiency in homes - using the same software the government uses to create EPCs, the Domestic Energy Model, and dynamic simulation modelling. They carried out physical tests to determine the energy performance and compare this with the EPC results.
The team measured the impact on airtightness of properties, and the fabric heat loss - using the blower door test, the new Pulse test for airtightness, the Leeds Beckett Coheating test and new QUB test to assess fabric heat loss.
The DEEP project found that insulating the solid walls of a home can achieve EPC Band C and could save up to 30% per year for some homes on their energy bills. It was by far the single most effective retrofit measure for solid walled homes – it was the only measure that gave a statistically confident finding, and the only one that, by itself, could raise the EPC to a C.
The DEEP project confirms that using the whole house approach and following the PAS2035 process will reduce the likelihood of risks occurring in homes after they’ve been retrofitted.
Before retrofit, 66-89% of the junctions in solid walled homes were already at risk of condensation forming. Following the solid wall insulation, the risks fell to between 16-22%. Following the PAS whole house approach reduced the risk to between 1-8%. Overheating was also found to be less severe.
The project identified improvements to the models used to produce EPCs - and how to make risk assessments more robust. Current EPCs assumed the test homes were less efficient than the tests determined, which could mean that energy savings from retrofits may be less than expected. Dynamic models were much more accurate.
In the DEEP test houses, 26% of the total retrofit costs were repairs and measures that had to be taken before installing the retrofit. A thorough survey, including an airtightness test, will maximise the performance of retrofits.
In testing airtightness and fabric heat loss, the researchers gathered useful information around the new Pulse and QUB tests for future use in assessing retrofits.
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 due to its cost and difficulty to install. This research demonstrates how important solid wall insulation is for the nation.
DEEP has also:
The project findings on solid wall insulation can be used by practitioners, academics, policy makers and householders to ensure nationwide retrofits are delivered safely and effectively, improving people's lives, and helping the UK on our journey to net zero.
DEEP Project Research
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