How should you assess timber when measuring embodied carbon?

As embodied carbon returns to the political agenda, TDUK offers advice on how architects and engineers can accurately assess the embodied carbon associated with timber buildings and building products.

The Embodied Carbon Bill, re-introduced to Parliament in June, aims to make it mandatory to report the whole-life carbon emissions of buildings, as well as introducing legal limits to reduce the level of embodied carbon in buildings and construction products.

Architects and specifiers are likely to be required to build to these limits. The Timber Development UK (TDUK) Technical Paper ‘Assessing the carbon-related impacts and benefits of timber in construction products and buildings’ can help.

It explains how to account for carbon in timber buildings and Environmental Product Declarations (EPDs) using the latest European Standards and the RICS Professional Statement on whole-life carbon assessment in the built environment.

Charlie Law, Sustainability Director at Timber Development UK, says: “This paper seeks to help clarify how the standards require us to account for embodied carbon within timber buildings and structures so we can better understand, measure, and address these emissions to reduce their environmental impact.”

What is embodied carbon?

Embodied carbon is the carbon dioxide (CO2) emissions associated with all materials and construction processes involved in the lifecycle of a building or structure. This includes the emissions involved in the manufacture and transport of all building products – effectively becoming the carbon footprint of the building during the original build, as well as any CO2 involved with the building’s maintenance, renovation and its ultimate demolition.

Counting sequestered carbon

TDUK’s Technical Paper explains that if timber is sourced from a sustainably managed forest, then the sequestered biogenic carbon stored in the product can be considered part of the assessment. If not, the timber does not have the benefit of any biogenic carbon sequestration.

Sequestered carbon is considered to enter the system when the timber is harvested and this is reported with the impact indicator, Climate change – biogenic (EN 15804+A2) or the Global Warming impact indicator (EN 15804+A1). The removal of CO2 from the atmosphere is considered a use of the resource.

All the processes of forestry are accounted for, including growing and harvesting the timber and maintaining the forest. Carbon sequestration is also reported as this is the point at which the biomass enters the technosphere.

As the construction product leaves the factory gate, the amount of sequestered carbon within the product should also be reported separately in the EPD, subject to some conditions.

Timber and the building’s lifespan

The amount of time that sequestered biogenic carbon will stay stored in timber products depends on the end of life treatment. Timber manufactured into particle board or insulation at end of life will keep the carbon locked in that product for another cycle. But timber that is sent for use as biomass fuel will release that carbon back into the atmosphere. If a building has been specifically designed for deconstruction, then it should be possible to reuse more products and components than if the building is of a conventional design.

Reporting at building level

If an assessment of embodied carbon is undertaken at building level, carbon sequestration, biogenic carbon emissions and removals are considered throughout the building’s lifecycle. But if only upfront carbon is assessed at building level, then the biogenic carbon sequestered in the products should not be included. TDUK worked with Jane Anderson of ConstructionLCA to develop the paper, which members can download free at ttf.co.uk/download/tduk-technical-paper