EMBODIED CARBON | FAADES CLEARER COMPARISONS A new methodology for calculating embodied carbon in faade systems aims to ensure life-cycle assessments are consistent and can be compared with industry benchmarks. CWCTs Teni Ladipo and David Metcalfe explain I n June 2022, the Centre for Window and Cladding Technology (CWCT) announced that it had established a dedicated sustainability workstream of contractors and consultants to write an embodied carbon calculation methodology for faades. In September 2022, the first issue of this methodology, How to calculate embodied carbon of faades: A methodology1, was published for design and construction professionals. This guidance, developed through collaboration with industry experts and a rigorous peer-review process, is a vital document. It provides a consistent embodied carbon methodology to allow for a better and more accurate understanding of the environmental impact of faades, comparative option studies, quantification of improvements, and target setting. The process overview can be seen in Figure 1. The methodology required interpretation of existing European standards BS EN 15978 and BS EN 15804, to ensure principles on the assessment of the environmental impacts of buildings within these standards are applicable to the complexities associated with faade assessments. It is anticipated that the results of assessments undertaken using the CWCTs methodology will feed into broader, project-wide whole life carbon assessments, so it was also important that the document aligned with widely referenced industry guides created for other building elements, to provide a degree of consistency. While alignment and interpretation of existing standards was important, there were additional considerations that the CWCTs methodology had to include to capture the level of detail and approach required for an accurate faade life-cycle assessment (LCA). These included: Scope: The methodology concerns the assessment of faade systems, commonly referred to as external walls or part of a building envelope. All components in a complete faade system assembly required to meet the functional, technical and aesthetic performance of the faade must be considered in a LCA. Life-cycle stages and modules: As many life-cycle modules as possible must be considered in faade More than 3,500m2 of faade panels were dismantled and refurbished during the revamp of 1 Triton Square LCAs. However, considering the significance of certain modules over others when assessing faades, the CWCT guide defines that lifecycle modules for product [A1-A3], construction [A4-A5], replacement [B4] and end-of-life [C1-C4] must be in the assessments as a minimum. Assessment approach: At the early stages of a design, there is greater uncertainty about quantities and sourcing of materials and components. To address this, three approaches are defined to guide how embodied carbon can be assessed while addressing information gaps and limitations at time of assessment (see panel, Approaches to assessing embodied carbon in early design stages). Offsite emissions: Faade system assembly and wastage can occur on and off site. This may be the result of the type of faade system and complexity of the supply chain required to fabricate and assemble the faade. Product stage offsite emission factors are included within the guide to allow required offsite emissions associated with producing a faade to be accounted for if applicable. Uncertainties: A carbon calculation scale-up factor is strongly recommended to account for potential underestimation because of various uncertainties that are more prevalent in early design stages for example, unconfirmed supply chain and bespoke elements. The magnitude of the carbon calculation scale-up factor may be reduced through the design process to reflect changes in the level of uncertainty. This factor is a separate parameter from a material uplift factor. www.cibsejournal.com December 2022 33 CIBSE Dec 22 pp33-34 Facade embodied carbon.indd 33 25/11/2022 16:15