Why carry out retrofit evaluation?

Why carry out retrofit evaluation?

Retrofitting our existing buildings to reduce their energy usage and improve the quality of life for their occupants is a key area to target if the UK is to reach its target of net zero carbon by 2050, which was enshrined in law in 2019. In 2019, buildings accounted for 30% of the UK’s emissions, with 23% of this produced by heating buildings[1].

Building new homes to higher standards will be set out in the upcoming interim update to Part L of the Building Regulations, intended to be released in December 2021 and come into force in June 2022. Ensuring newly built homes meet higher standards is an important step in minimising emissions from future homes, particularly with a commitment to building 300,000 new homes a year by the mid-2020s set out in the last conservative manifesto[2].

However, the Committee on Climate Change (CCC) notes that “the 29 million existing homes across the UK must be made low-carbon, low-energy and resilient to a changing climate”[3], and it is clear that retrofitting our existing homes to reduce their energy usage will be a key area to address to allow the UK to achieve its target of net zero by 2050.

Retrofit evaluation

Retrofitting existing homes to reduce their energy consumption can be done in a number of ways, with a fabric first approach being widely favoured. Fabric first involves upgrading the performance of the existing building fabric (through installation of better performing, and often thicker levels of insulation) before looking at other areas to address, such as low-carbon heating.

Discussing the merits of different approaches is beyond the scope of this article; however, it is essential that the impact that retrofit measures have are recorded, both in qualitative assessments (such as occupant questionnaires) and quantitative measures (such as measuring energy usage or thermal performance of a property). You can’t manage what you don’t measure, so implementing evaluative assessments of retrofitting measures is crucial in proving their effectiveness and, crucially, developing a cycle of improvement to fine-tune the building and inform future retrofit projects.

In article Retrofit Eval

PAS 2035, the over-arching document in the retrofit standards framework which was introduced following the recommendations of the Each Home Counts review, requires that evaluation of the retrofitting process is carried out as part of its process. The Retrofit Coordinator has to ensure that every retrofit project is subject to monitoring and evaluation, with monitoring and evaluation carried out by a Retrofit Evaluator. Basic monitoring and evaluation (using occupant questionnaires) is to be carried out for every completed domestic retrofit, whilst intermediate is to be applied to projects for which the basic assessments indicate that the outcomes are different from those originally intended, or there are unintended consequences of the retrofit work. Advanced monitoring and evaluation is reserved for those retrofits where intermediate methods indicate that further investigation is required to resolve any discrepancy between predicted performance and outcome performance. Only once sufficient evaluation has been undertaken can a retrofit project claim PAS 2035 compliance, required under government scheme initiatives such as ECO?


Evaluating the performance of any retrofit project is key to understanding how the methods implemented interact with that particular building, and to develop a continuous cycle of improvement that benefits both the project in question and future retrofit projects. Going to the lengths to reduce the energy usage of a building, but then not accurately determining whether the measures have actually made a difference is a nonsensical move, thus the requirement for monitoring and evaluation detailed in PAS 2035. Retrofit evaluation and post-occupancy evaluation (of new buildings) are key tools that must be utilised correctly to realise a reduction in energy usage, and thus carbon emissions, from buildings. Successful implementation will go a long way in helping the UK tackle its carbon footprint, and ultimately in its target of net zero by 2050.

Find out more about Retrofit Evaluation

[1] Heat and Buildings Strategy. (2021). Source: UK Gov.

[2] Conservative Manifesto. (2019) Source: Conservative Party.

[3] UK housing: Fit for the future? (2019). Source: Committee on Climate Change.

Article published 04/11/21

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