The construction sector is a major contributor of carbon emissions. Pressure to respond to the climate emergency means that decarbonisation is a priority for everyone who has a stake in construction. But where to start?

By James Moxey, Woodknowledge Wales, 6 May 2020 

Organisations considering a decarbonisation strategy that aims for low carbon or even net-zero carbon buildings are well advised to focus their attention in three key areas: Embodied Carbon, Operational Carbon and Offsetting. This article aims to explain what this entails.

Embodied carbon – the material question

Firstly, this means considering the carbon emissions associated with construction materials, e.g. timber, steel, concrete, brick, plastic. This is known as embodied carbon.

Timber used in buildings stores carbon

The embodied carbon refers to emissions that are occurring before a building is occupied as well as such associated with the demolition of the building.

Carbon emissions from the extraction, manufacture and transport of construction materials and components are known as up-front carbon. Carbon emissions occurring after demolition are known as end-of-life carbon.

Construction materials vary widely in their carbon emissions and energy use. Concrete, for example, is associated with high levels of embodied carbon globally, due to the very large volumes used. Research suggests that it is responsible for 8% of global emissions. Timber on the other hand, harvested from sustainably managed forests, captures and stores carbon from the atmosphere (so called biogenic carbon) when used in buildings. This reduces the impacts of climate change. Its manufacture also emits very low levels of carbon and at the end of life, timber can be re-used, recycled or used for energy recovery. At this stage, the biogenic carbon will be transferred to the next product system or emitted resulting in a biogenic carbon balance.

There are various methods to accurately evaluate the embodied carbon of individual construction materials. Woodknowledge Wales will soon publish industry guidance on this to help organisations implement a low carbon or zero carbon strategy. Stay tuned!

Operational Carbon – tackling lifetime energy use

Once you’ve solved the material aspect of your decarbonisation strategy, you will need to take a closer look at emissions deriving from the use of your building.

Hence a second key activity is to design and build in a way that means less operational energy is used during a building’s lifetime. Operational energy comprises energy from any source, whether in the form of electricity, gas or oil, which is used to heat a building during colder periods, to cool it during hotter periods, or to heat water. Due to the use of fossil fuels such as gas, this energy is associated with carbon emissions. These emissions are known as operational carbon.

Operational energy consumption can be reduced if careful consideration is given to both the design of the fabric of a building (known as fabric first approach) and the shape, layout and orientation of the building itself. This is part of a suite of overall measures that include achieving thermal performance; control of air tightness; air quality for comfort and well being; and acoustics.

Micro-renewable technology (such as solar panels) has a part to play in providing energy needs for UK housing. However, its use should be considered in the wider context of a national grid that is itself decarbonising.

Tree seedlings

Tree seedlings ready for planting

Offsetting – completing the final mile

Once both the embodied and operational carbon have been considered, a third stage will help move towards the desired goal of a true zero carbon building. Even the most sustainable buildings are likely to emit some carbon at some point over their life cycle. Offsetting, via a recognised framework, enables any remaining emissions to be compensated for by, for example capturing carbon elsewhere e.g. through tree planting. The net emissions of our new buildings are therefore balanced with compensatory planting – an exciting holistic prospect for environmental development.

Carbon assessment and RIBA stages of work

These three activities considered at the design stages (e.g. RIBA Stages 0-4) can underpin a more formal Whole Life Carbon Assessment – a very useful tool that allows the best sustainable building options to be considered. It will also provide the objective evidence needed to demonstrate the environmental credentials of a development e.g. by benchmarking against the RIBA 2030.

Furthermore, building performance testing carried out at RIBA stage 7 can take this work a stage further by gathering operational performance data within a building once constructed. This allows clients and tenants to better understand how their buildings perform in reality.

Case Study

Clwyd Alyn social housing project in Llanbedr near Ruthin constructed by Williams Homes

Read our case study here on a Clwyd Alyn Housing Project delivered by Williams Homes Ltd at Llanbedr. This is a 36 unit housing development using home-grown Welsh timber which surpasses RIBA 2020 Climate challenge targets for embodied carbon.