Calculating carbon is complicated. Working out the embodied carbon of a building product is more complex than simply taking one figure from a report. However, the first step to accurately comparing the embodied carbon of different building products is to have a level playing field for carbon reporting.
Embodied carbon guidelines
To determine the carbon embodied in a particular product, the construction industry relies on established guidelines and technical guidance in the form of product category rules (PCRs), and environmental product declarations (EPDs).
PCRs provide the category-specific guidance for estimating and reporting product lifecycle environmental impacts. EPDs disclose the life cycle environmental performance of products using pre-determined parameters.
The quality of the information in the EPD must be verified by a third party before it can be registered and published.
A major challenge for specifiers is that the data found in EPDs can vary significantly.
Inconsistencies in calculation
Comparing EPDs for different products can be complicated as there are elements that may not be consistent from one EPD to another. For example, different methodological approaches may be taken; generic rather than product-specific data may be used, and non-required fields - such as A4 Transport - may be included in some EPDs and not others.
Inconsistencies in information contained in an EPD can have a major impact in terms of product specification. This is particularly true when comparing biogenic products such as timber with products manufactured using other materials, and critically, it will impact the figure for carbon embodied in a building.
This is highlighted in a report published by engineering consultancy LBP SIGHT, which analysed 48 EPDs for wood products. The report Carbon Accounting for Building Materials - An assessment of the Global Warming Potential of biobased construction products, states: "The assessment of PCR and EPDs of wood-based products shows that inconsistencies both at the system level of PCR and the implementation in EPDs exist. Ultimately, this results in skewed declared values for CO2e emissions at the product level, and therefore in comparison with alternative products".
RICS standardisation of LCAs
The RICS Whole life carbon assessment (WLCA) for the built environment, section 4.7, explains the types of carbon data that should be used in a WLCA . It recommends the Built Environment Carbon Database as the first point of reference to identify carbon data for construction materials and products. According to RICS, EPDs using EN 15804 and ISO 21930:2017 are preferred.
EN 15804 requires all product EPDs that contain biogenic carbon to be modelled on their full life cycle. The RICS WLCA does allow for Cradle-to-Gate EPDs, but only if biogenic carbon is totally excluded.
It is worth noting that the older version of EN 15804, which dates to 2013, used to allow Cradle-to-Gate for biomass materials. This has allowed some timber products to report carbon credits instead of impacts, which can be misleading where legacy EPDs are referenced.
An EPD produced in accordance with EN 15804 must also comply with the requirements of ISO 14044, the International Life Cycle Assessment (LCA) standard, and ISO 14025, the international standard covering EPDs for construction products.
The standard EN 15804 defines a series of modules covering carbon emissions over a product's various lifecycle stages:
• A1-A3 production stage
• A4-A5 construction stage
• B1-B5 use stage
• B6-B7 operational carbon stage
• C1-C4 end-of-life stage.
H+H has ensured that our product EPDs cover each of these sections to transparently report the full lifecycle, Cradle-to-Grave, of our products. We believe that product manufacturers have a responsibility to report as accurately as possible the environmental impact of their products across their full lifecycle. However, there is still work to be done by regulatory authorities to ensure a level playing field for all embodied carbon reporting in the construction sector.
The continued variation between EPDs only emphasises the importance of standardised methodologies and high-quality data in EPDs to ensure meaningful and accurate comparisons.
Sources
LBP Sight. Carbon Accounting for Building Materials: An assessment of Global Warming Potential of biobased construction products. 2022. https://www.ca4bm.eu/CA4BM_Final_Report.pdf
RICS. Whole life carbon assessment (WLCA) for the built environment. https://www.rics.org/profession-standards/rics-standards-and-guidance/sector-standards/construction-standards/whole-life-carbon-assessment.html)