Demonstrating retrofit improvements

Demonstrating retrofit improvements

It is estimated that 27 million homes in the UK need retrofitting, roughly 900,000 homes per year from 2020 to 2050, in order for the UK to achieve net zero carbon by 2050. That equates to 2466 homes per day, or 1.7 homes per minute, every minute for 30 years[1]. This is clearly a monumental task, and a key aspect of this is demonstrating that the measures being installed as part of retrofits are actually resulting in an improvement to the property. There are a variety of methods that can be used to monitor and evaluate retrofit measures, with varying degrees of invasiveness for the occupants.


The simplest (and cheapest) method of evaluating the performance of a retrofit is to ask the occupants how they think it has changed. Effective questioning that allows for both quantitative and qualitative responses to build up an overall picture of the occupants experiences is an easy way of determining the project’s success, as ultimately it is them who will be experiencing the tangible changes a retrofit can deliver on a daily basis.

Air-tightness testing

Poor air-tightness of properties is a leading cause of excess heat loss from properties. Poorly sealed properties are often draughty, causing thermal discomfort for the occupants. Retrofit projects can aim to increase the air-tightness of the property in order to reduce heat loss through the envelopes, particularly around thermal bridges. The basic principle is to increase the air-tightness of the property, demonstrated by taking pre and post retrofit measurements. Consideration must also be given to ensure adequate ventilation is still provided for the occupants, and also to avoid the possibility of mould.

Energy usage monitoring

Simply put, monitoring the energy usage of the property before and after the retrofit should demonstrate the direct impact on energy used in the property that the retrofit has had. Clearly, if the energy usage has decreased after the retrofit, it provides good evidence that it has reduced the energy usage of the property. It is crucial that the monitoring periods are comparable, taking into account the time of year and occupancy factors as best they can, although clearly these will not be ‘test’ conditions. 

Co-heating tests

Co-heating tests are used to measure heat loss through the envelopes of a building, giving an as-built performance metric rather than those produced from calculations such as SAP. As a result, it can be used to directly measure the heat loss both before and after a retrofit measures have been installed. Using accurate, on-site measurements rather than calculated is much more desirable, giving the retrofit team real-life feedback on the performance of the property. Co-heating tests are quite invasive, however, so alternative options, such as the use of SmartHTC (which allows the occupants to remain in the property whilst the measurements are done) that produce measured heat loss results are much more viable and scalable for larger retrofit projects.  

Thermographic surveys

The use of infrared imaging to conduct a thermographic survey of the property prior to retrofit works taking place will help to identify the ‘low-hanging fruit’ that can have a large impact for minimum cost, such as poorly sealed jambs around windows and doors. Once these are identified by the thermographic survey and rectified, a second thermographic survey can be done to confirm the works have actually addressed the issues.

Internal condition monitoring

Monitoring the internal conditions within the property prior to retrofit works taking place allows for a baseline to be established and any thermal discomfort issues identified. Retrofit measures should result in the improvement of thermal comfort for the occupants, and monitoring the internal conditions after the retrofit works will ideally prove that the works have had a tangible impact on the internal conditions.


Demonstrating retrofit improvements should be done using a multi-faceted approach, taking into account different factors that are important in determining the success (or failure) or a retrofit project. Assessing the property prior to the retrofit works taking place is necessary to establish a baseline against which the retrofit works can be compared, so monitoring and evaluation must be considered at the start of a project, not as an afterthought.

[1] The Retrofit Toolkit: Helping Local Authorities to Kickstart Deep Retrofit. The Retrofit Academy.

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Article published 07/12/21

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