Do you understand Whole Life Carbon Assessments? This article, adapted from one of our new Timber Knowledge Sheets, introduces the basics of WLCAs
Incorporating low embodied carbon materials, such as timber, into a building’s design can make a significant contribution to the reduction of embodied carbon in the built environment.
The storage of biogenic carbon within sustainable timber used in buildings is also beneficial, as it keeps this carbon out of the atmosphere for an extended period of time.
There are four key stages to a Whole Life Carbon Assessment:
- Product Stage (A1-A3)
- Construction Stage (A4-A5)
- Use Stage (B1-B7, which includes operational carbon
- End-of-life Stage (C1 – C4)
There is also a Stage D, which looks at the impacts beyond the assessment cycle, but this data is not included in the overall whole life carbon calculation.
Product Stage (A1-A3)
The product stage covers the carbon emissions associated with all the processes required to produce the timber product, including planting the tree and managing it to maturity, harvesting, transportation to the manufacturing facilities, and all manufacturing facility operations such as sawing, kiln drying, and fabrication.
If responsibly sourced timber is used (e.g. FSC, PEFC or Grown in Britain certified timber), then the sequestered biogenic carbon stored within the product can also be
considered as part of the Whole Life Carbon Assessment, where it is included in A1 as a minus figure (carbon removal).
This biogenic carbon figure must also be highlighted in the report as a ‘Stored Carbon’ figure.
However, if the timber is not sustainably sourced, the sequestered biogenic carbon benefit cannot be taken into account.
Construction Stage (A1-A5)
The construction stage covers the carbon emissions associated with transporting the product to site, and placing this within the final structure, such as the emissions from plant and machinery, and any waste which arises on site.
Use Stage (B1-B7)
The use stage covers the carbon emissions associated with the product once installed. Therefore if the product needs maintaining (e.g. regular painting) or needs to be replaced at some point over the life of the building (e.g. if timber cladding needs to be replaced after 30 years) then the embodied emissions from the new products, and any plant and machinery used to apply these new materials, needs to be included.
This stage also includes operational carbon emissions. However, it is unlikely that any timber product will have any operational carbon emissions.
End-of-Life Stage (C1-C4)
The end-of-life stage covers the carbon emissions associated with the removal of the product from the structure, transport to a processing site, any processing required for it to reach an end-of-waste state, and end disposal (if applicable).
Where the product contains biogenic carbon (all timber) this is transferred out of the system at this point, either as a transfer to another system (e.g. reused or recycled timber in C3) or an emission (e.g. timber going to landfill in C4).
Therefore, for responsibly sourced timber, the biogenic carbon figure subtracted in A1 is added back in at either C3 or C4, thereby resulting in a net biogenic carbon balance (-1/+1).
However, if the timber has not been sustainably sourced, this will result in a significant biogenic carbon figure, as no sequestration would have been allowed in A1 (-0/+1).
Based on 2021 data from the Wood Recyclers Association (WRA) and the EA Waste Interrogator, timber is likely to follow these end-of-life routes:
- Biomass with energy recovery (includes assumed RDF) (C3) – 67%
- Recycling into panel boards (C3) – 24%
- Recycling into animal bedding (C3) – 8%
- Landfill (C4) – 1%
However, different timber products are likely to follow different end-of-life routes depending on their makeup. The table opposite shows the likely end-of-life route for different timber products.
Beyond Building Lifecycle (D)
Stage D looks at the benefits and impacts beyond the building lifecycle. For example, for energy and incineration, the avoided impacts of any heat or electricity recovered
from the process are considered. However, data from stage D is not included in the overall whole life carbon calculation.
Upfront Carbon Assessments
In some circumstances, only an upfront carbon assessment is carried out on a building. If, when assessing only upfront carbon (Stages A1–A5), the biogenic carbon is included, the result can potentially show what appears to be a carbon negative outcome.
Therefore, when assessing only upfront carbon, the sequestered biogenic carbon must not be included in A1 of the assessment. However, the biogenic carbon figure must still be highlighted in the report as a ‘Stored Carbon’.
This is a excerpt from the Timber Knowledge Sheet ‘Timber and Embodied Carbon’ which can be downloaded here. It also explains Environmental Product Declarations (EPDs), carbon sequestration and provides a clear introduction to embodied carbon.
For more detailed information on assessing the carbon related impacts and benefits of timber, see the TDUK Technical Paper: Assessing the carbon-related impacts and benefits of timber in construction products and buildings