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Thought Leadership

The Retrofit Toolkit in action

Min Read
Robert Hopkins - Director, Architecture

by Robert Hopkins

Director, Architecture


Our Retrofit Toolkit was developed as a response to the growing appetite to consider retrofitting the existing UK building stock to Net Zero Carbon (NZC).

For context, it is expected that the current building stock in the UK will form around 80% of our buildings in 2050 when the UK will be fully NZC. Demand is set to grow exponentially to be able to upgrade these buildings to the standards required by NZC.

Find out how our toolkit can help you

The availability of energy to heat buildings will also decrease significantly as the gas network is superseded by the renewable electricity grid, meaning that there will likely be no choice in buildings consuming less energy.”

The first of our retrofit studies considered a typical school building completed in 2000

The challenge set was to propose six interventions which could upgrade the building to a NZC level of 65 kWh/m2.yr whilst also being able to provide a business case to support this. The building was typical for the time being 5,000 m2 in area over three storeys and constructed using a steel frame and traditional masonry construction.

A methodology was established which first took the data available for the existing building and developed this into an energy model. This shared parameters such as an energy use intensity of 160 kWh/m2.yr, an air leakage of 10 and u-values commensurate with the minimum building regulations required at the time of construction.

Once the energy model had been developed by our partner engineer, a series of interventions were considered which considered both the ability to deploy the change and the architectural implication of doing so. First, potential fabric upgrades were tested, then MEP upgrades and finally, whether renewable technologies could be added to get the building from a NZC operation to fully zero carbon.

The findings

The findings considered interventions with different levels of performance and balanced these with capital cost, O+M costs, operational carbon savings and embodied carbon required to implement the upgrade. The top six upgrades were then clearly defined, bringing the EUI of the building from 160 kWh/m2.yr to only 65kWh/m2.yr.

The findings were summarised in a simplified chart which forms the main basis of the Retrofit Tool output. The contents of the chart were developed to support decision making by client teams and to give any additional data which may be required for specific approvals, whether this is for schools, universities, housing associations, funders or developers.

Finally, an option to add renewables to the school was applied which took the EUI from 65kWh/m2.yr to zero. This was based upon the ability to apply PV panels to the pitched roof of the building, using readily available panels.


The conclusions of the study showed that this approach could be taken across a variety of buildings and sectors. With the tool assisting in first establishing whether it was possible to upgrade an asset to NZC and then specifically what needed to be done to achieve this.

In breaking these down into manageable elements, a challenging process is made to feel achievable with clear information available on which to make more informed decisions.

Posted on:

Feb 3rd 2023


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