Emissions from the construction and use of buildings contribute about 40% of global carbon emissions. As other sectors decarbonise, buildings-related emissions are projected to account for around 90% of global emissions by 2050.  In the UK, four fifths of buildings around today are expected to still be in use in 2050. With the UK having among the most energy inefficient housing in Europe, retrofitting existing buildings is a government priority. However, little attention has been given to the overall environmental impact of delivering the retrofits themselves. In this article, Dr Mithila Achintha discusses his work with the Greater Manchester Combined Authority (GMCA) on tackling embodied carbon of home retrofitting, and how lessons learned from the COUNTER project can shape retrofit policy.

• About 10% of UK’s emissions are from the production and use of construction materials, more than the combined emissions from aviation and shipping.
• Despite this, the government does not require new construction or retrofit projects to have an assessment of embodied carbon.
• Academics from The University of Manchester have developed a carbon calculator which is already helping to identify energy efficiency measures with the lowest life-cycle embodied carbon emissions.

 Home energy retrofits  

The government’s Warm Homes Plan, which seeks to lift one million homes out of fuel poverty, has been put on a firm footing by government, being part of the government’s mission to make Britain a clean energy superpower. As part of the plan, the government has announced its intention to raise minimum energy performance standards for private and social homes by 2030, funding some individual retrofits through local authority grants.

While these steps are necessary, the government does not require new construction or retrofit projects to carry out an assessment of the project’s embodied carbon. Embodied carbon is all emissions associated with the production, installation, maintenance, repair, demolition and disposal, and life beyond the current cycle of a material, product or project. Embodied carbon associated with the construction industry already accounts for around 10% of UK emissions, and without action these emissions will likely account for almost all buildings-related greenhouse gas emissions by 2050.

Counting carbon

Led by The University of Manchester in collaboration with the GMCA, the COUNTER project created a carbon calculator for quantifying whole life-cycle embodied carbon. The carbon calculator has been designed specifically with energy efficiency measures in mind, such as solar panels, heat pumps and wall insulations used in government-funded social housing retrofitting projects. The research findings show that the amount of time an energy efficiency measure needs to be in use for, in order for the emissions reduced from lower consumption to outweigh those from resource use, is up to seven years, due to the high levels of embodied carbon. Without action to dramatically reduce the embodied carbon footprint of housing projects, delivering net zero homes will not be possible. The results of the project also show the importance of considering end-of-life and life beyond current life in the calculation of carbon footprints – this is beyond the current practice of focusing on carbon emissions at material/product stage only.

The carbon calculator has also been used to compare the different products of the same retrofitting measure per unit of energy saving. With the example of solar panels, the calculator takes into account the distance the product will need to be transported and the materials used to estimate the emissions per product. Solar panels also come with different electricity generation capacities. To make decisions on actual carbon impact the calculator compares on a per unit basis. For instance, while a solar panel with a 400W capacity may be associated with higher absolute embodied carbon compared to a 200W panel, if you calculate the embodied carbon per watt, then a 400W panel may be a better option. Overall, the results show how combinations of life cycle modules can be chosen to make reliable decisions on materials/products that ensures the lowest embodied carbon among available options.

The carbon calculator is already being used by government organisations. The retrofit team at the GMCA, local authorities and social housing providers have been up-skilled on the impact of embodied carbon, and the calculator now forms part of their Net Zero Housing Retrofit Framework Agreement. Over 10,000 homes in Greater Manchester are set to benefit from the specification of low embodied carbon over the next three years, with other local authorities, combined authorities, and social housing providers able to adopt the framework.

Next steps for local and national government

The UK’s Construction Strategy expires this year. This represents a key opportunity to update government policy, and ensure that the UK’s buildings related emissions achieve net zero on a whole-life basis.

For local authorities and mayoral combined authorities, embodied carbon should be included in the list of criteria when awarding contracts for retrofits. The GMCA has already done this, by incorporating the embodied carbon calculator into its retrofit procurement framework. Other local and mayoral authorities, and social housing providers, could adopt a similar approach.

Currently, there is no requirement to declare the embodied carbon footprint in retrofit or construction projects. To address this, the government should introduce mandatory reporting of embodied carbon through Environmental Product Declarations (EPDs) for materials and products, and for the total embodied carbon of overall projects, ensuring that life cycle stages are included in this.

Additionally, complex regulations and poor data availability have created a challenging environment for retrofits and low-carbon construction. The government could ameliorate this by streamlining building regulations as well as providing benchmarks for embodied carbon levels for new builds and home retrofitting. This could look like mandating an acceptable level of embodied carbon per square metre of floor in a new build home, or per unit of energy saving from enhanced insulation. Further, manufacturers and suppliers should be required to provide end-of-life scenarios of the materials and products.

Over the longer term, there are technology gaps which should be filled. To address this, grant funding should be made available for exploring bio-based and waste-based construction materials and products in construction as the most reliable means of reducing embodied carbon.