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EON Retrofit Test House: Impact of order of retrofit measures

Solid-wall, ‘hard to heat, hard to treat’.


This case study is part of the CALEBRE project, 'Consumer Appealing Low Energy technologies for Building REtrofitting', which focused on solid wall 'hard to heat, hard to treat' properties.

The project considered a range of current, medium and longer-term technologies for domestic energy efficiency refurbishment, with the perspective of the householder at the heart of all thinking and decision making.


The operational performance of retrofit measures can depend on the other energy-saving measures that have been installed in a property. It is therefore important to consider the order in which measures are adopted, to ensure that maximum energy saving can be achieved.

The case study team undertook thermal dynamic modelling to assess the energy savings and associated carbon dioxide savings of applying retrofit technologies in the EOn Retrofit Test house in different orders.

Three retrofit approaches were considered:

  • insulation driven
  • affordability driven
  • installer experience driven,

each with seven stages of intervention at three year intervals from 2012 (base case) to 2033.


While the end (2036) annual energy performance for all three approaches is similar, the three year stage results show how some intervention measures made more of an impact on energy consumption than others.

For example, replacing the boiler early in the retrofit order means that subsequent heat-saving measures which reduce the heat load of the building may mean that the selected boiler becomes oversized and consequently less efficient.


This case study modelling work suggests that early implementation of measures which significantly reduce annual energy consumption (e.g. external wall insulation, double glazing), yield the greatest benefits with regards to cumulative savings.

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