The road to true net zero

As construction works towards reducing carbon emissions, John Smith, technical director at Donaldson Timber Systems, discusses why embodied carbon is critical to its success

IT’S been a long time coming, but the journey to net zero carbon homes is well underway.

Over the summer, the Scottish Government published a new version of Building Standards for Domestic Buildings, with changes to standards for energy performance, ventilation, and overheating effective from 1 December. By 2025, all newly built homes will need to be ‘zero carbon ready’, with a 57% reduction in carbon emissions to 2021 levels, in preparation to reach Scotland’s ambitious net zero target by 2045.

Reducing the requirement for energy in the home is the first step to achieving this, before introducing low and zero carbon energy sources to provide heating and power.

Fossil fuel boilers will be banned in new homes in Scotland from 2024, with a shift to new heating systems like air source heat pumps. These heating systems are only efficient with a high performing building envelope, so the introduction of a Fabric Energy Efficiency measure within these latest changes is a necessary, and welcome step.

At Donaldson Timber Systems (formerly Stewart Milne Timber Systems), we’ve been advocating for this build method for over 15 years. Our BOPAS Plus accredited and BBA certified Sigma® II Build System uses only fully recyclable materials and is designed to achieve superior levels of fabric performance, suitable for projects which are seeking to achieve the very highest fabric efficiency, airtightness standards, and sustainable credentials.

Embodied carbon

While these updated standards are a much-needed step in the right direction, more clarity is required on what is really meant by zero carbon, or carbon neutral. When we talk about ‘zero carbon’, we should really be thinking about the cradle to grave impact of the build and the unintended consequences along the way.

For us, the most crucial factor when it comes to reaching true zero carbon, is embodied carbon.

Embodied carbon is the total greenhouse gas emissions generated in production and manufacturing of an asset. It can be calculated in two separate elements: from raw material extraction through to construction of the building on site, including fuel and power for transport, factories and plant; and end-of-life emissions from demolition, transport from site and recycling/landfill.

In 2021, the UK Green Building Council (UKGBC) developed the Whole Life Carbon Roadmap for the Built Environment, which indicates that the impact of embodied carbon is set to increase and will form over half of built environment emissions by 2035. Despite this, embodied carbon emissions are currently unregulated in the construction industry, with only voluntary measurement and mitigation required.

In a new home completed to 2021 standards in Scotland, embodied carbon from the construction and end of life demolition and disposal is around 20% of the whole life carbon emissions, with the rest from the operational heating and power.

With a likely target to reduce emissions by 57% through operational carbon reductions, the embodied carbon becomes much more significant at up to 60% of the whole life emissions.

It is therefore crucial that the embodied carbon of new building designed for 2025 standards are understood, to ensure that any savings in operational carbon are not offset by the introduction of a building fabric with high embodied carbon.

Time for Timber

When we factor embodied carbon into the zero-carbon journey, timber really comes into its own. This is nothing original for new build homes in Scotland. Unlike England and Wales, over 90% of new build homes north of the border are constructed using timber frame, so Scotland is already one step ahead.

As the only naturally renewable building material, timber build systems are undeniably the most sustainable form of construction.

Using a timber frame build system for a 2021 new-build home reduces the embodied carbon by around five tonnes, compared to a masonry construction home of the same fabric performance.

This carbon saving will undoubtably increase as the building fabric performance is increased to achieve 2025 levels.

Timber frame homes are also more environmentally friendly during the build, when the building is in use and throughout its lifetime. Timber can also lower or offset its embodied carbon thanks to sequestration – absorbing atmospheric CO2 while the tree is growing and storing it until the timber is incinerated or goes to landfill at the end of its use. Around one tonne of CO2 is stored in every m³ of timber.

While we’ll continue to campaign for the legislation of embodied carbon, many organisations will reach the conclusion that they need to consider the full process to meet their corporate sustainability goals. In recognition of this, we’re working with our customers to help measure the sequestered and embodied carbon for all our build systems.

Through experience, measurement, and science, we can demonstrate that timber offers an ideal solution to achieve true net zero carbon targets.

Scotland is leading the way, and one day, all homes will be built like this.

John Smith