Total impact of greenhouse gas emissions in construction

Now is the time to clamp down on embodied carbon in construction


The Built Environment


BREEAM, energy efficiency, refurbishment and conservation, zero carbon

As the impacts of climate change rapidly escalate, we have much to do in the construction industry to alleviate its effect. Over the last few years there has been a greater emphasis on improving energy efficiency in our buildings and to create a greater capacity of renewable energy production. These measures, if adopted by all will help cut down the amount of carbon generated by fossil fuels used to run, light and heat buildings, however, this is simply not enough. We need to take a step back to see where further savings can be made. That is why the industry needs to consider the greenhouse gases that are emitted to construct our buildings in the first place, the embodied carbon. Examples of the type of carbon emissions caused by construction Embodied Carbon Lifecycle The embodied carbon of a building refers to the total impact of all greenhouse gas (GHG) emissions attributed to all materials during their lifespan from manufacturing, the energy used in construction, as well as consumption required to demolish and dispose of construction materials when the building is no longer needed. According to the World Green Building Council, embodied carbon accounts for 11% of global carbon emissions and 75% of a building’s emissions over its entire life. For the construction sector, tackling this environmental impact must be made an urgent priority. Building rating systems such as BREEAM recognise embodied carbon measurement and mitigation as part of minimising building life cycle impacts. This issue is a focal point behind a new campaign aiming to put embodied carbon on the political agenda and to introduce a cap on the amount of embodied carbon a building can have. The movement is being spearheaded by Architects Climate Action Network, a group founded by built environment professionals in 2019, which has grown rapidly to include more than 1,000 supporters across the U.K.Enacting regulation to limit embodied carbon emissions is a vital and necessary step that the government must take if the UK construction industry is to play its part in the fight to tackle climate change. It is a matter of when, not if, and we call on the government to act fast.” ACAN said. The foremost embodied carbon offenders are concrete and steel The carbon impacts of concrete and steel. Image credit: Carbon Smart The foremost embodied carbon offenders are concrete and steel, suggesting that most of a building’s carbon impact is in its frame and foundations. The manufacture of cement accounts for 8% of carbon emissions globally and steel smelting is mostly fuelled by coal. There are no quick fixes to limit the impact of either of these emissions and unfortunately using lower carbon materials is low down on the list of the best ways to reduce embodied carbon. However, systematically salvaging, and repurposing existing buildings would dramatically improve a building’s energy efficiency as the carbon emissions already embodied in them would not be lost through demolition. Buildings can serve a multitude of uses over their lifetime. Renovation projects traditionally save around 75% of the embodied carbon emissions when compared to the construction of a building from scratch. Most of the embodied carbon is held and accounted for within the foundations and structure if they are conserved. Many designers like to start with a blank canvas but channelling that creativity towards resurrecting a dilapidated building into something sustainable and energy efficient is equally rewarding. Secondary glazing should be considered in a renovation as it helps buildings retain their embodied carbon instead of adding more by knocking down and rebuilding. If a building is upgrading its windows, there are two options, if it is not Listed. It can either have all the windows replaced, which is going to incur two levels of embodied carbon; stripping the old windows out and replacing with new ones. Alternatively, the introduction of secondary glazing will retain the original windows, and therefore the embodied carbon is kept. The only addition will be the embodied carbon associated with the manufacture and installation of secondary glazing. Furthermore, secondary glazing can help reduce a building’s carbon footprint and heat loss problems, thanks to the low U-values for both the glazing and the frame. Selectaglaze was involved in the renovation of Farringdon Station in 2012, a project that proved the re-use and enhancement of existing materials cuts carbon emissions considerably. The station is positioned in a built-up commercial, residential and conservation area, and is itself a Grade II Listed building. A study by project managers Faithful+Gould, assessed the cradle to gate emissions of the refurb and found that preserving some of the existing façade saved a mammoth 3,000tCO2e. The largest sources of embodied carbon were the foundations, with total embodied carbon of 1,357tCO2e, followed by the ground floor construction with 823tCO2E. The frame, normally the worst embodied carbon offender, came in with only 761tCO2e, while the external walls even less at 520tCO2e. “This project shows that when something can be re-used there is usually an embodied carbon benefit,” says Sean Lockie, Director of Sustainability at Faithful+Gould.  2012 renovation of Farringdon Station. Preserving some of the existing facade reduced embodied carbon levels as shown in graph The adage of reduce, reuse, recycle is crucial when designing for construction to minimise waste and use existing or reprocessed products where possible. Adopting this approach can decrease the embodied carbon of demolition and salvaged materials, like brick, concrete, or metal typically have a lower embodied carbon footprint than newly manufactured materials since the carbon to manufacture them has already been spent. With reclaimed wood for instance, one not only saves the energy spent in cutting the tree down, transporting and processing it, but the saved tree can continue its work of sequestering carbon. The use of BIM to digitally construct a building could help in keeping embodied carbon levels at a minimum How much difference to carbon emissions could BIM make? Image credit: Tekla Technology can support the fight to reduce embodied carbon in construction. The use of BIM to digitally construct a building during the design stage can assist in identifying areas where lower carbon materials can be used. This in turn minimises any budgetary or resource-intensive miscalculations that could lead to unnecessary energy consumption and carbon emissions. BIM allows for a building to be efficiently demolished decades later because details of the products and materials used have been accurately documented. To conclude, while the points made above will make improvements, legislative intervention will really be the key to confronting the issue of embodied carbon. Major design decisions (e.g. the choice of structural frame) will not be decided predominantly by embodied carbon considerations, so more needs to be done to cap carbon levels in building projects. There needs to be incentives to push people to take measures, and overall, there needs to be a change in the approach to design as the whole building lifecycle needs to be thought through, as outlined in the RIBA Plan of Work 2020.