Guidance
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Cut-off rules should not be used to hide results. Therefore it is mandatory to provide verifications for excluded parts.The application of cut-off rules is always highly dependent on the specific circumstances and the product; no general approaches can be defined, but some PCR documents for EPD or labelling schemes define specific cut-off rules, or the extent of the materials and products that should be included. Information from these sources can be stated when the exclusion of materials and products is justified. If appropriate data are available, they should be included in the LCA. If not, then conservative assumptions should be made, and documented transparently. If no appropriate data are available at all, cut-off rules can be applied and the respective aspect can be left out, which should be documented transparently with very special care when comparing product systems (ISO 14044: 4.2.3.3.3).
1) Specific guidance for product LCA studies
Cut-off rules for building product LCA can be defined, e.g. for the exclusion of capital equipment of the production plant, or the exclusion of ancillary materials such as plastic packaging of a raw material in the upstream processes.Practitioners should refer to the existing common rules in the background LCI database for the cut-off rules that should be applied. Generally speaking, the background data should not be modified to comply with the cut-off rule of simplified approaches such as EN 15804. The cut-off rules are defined mainly to ease data collection and modelling for the foreground data. For specific applications such as EPD, generic background data may be pre-verified, i.e. the cut-off rules are compliant with the PCR/EPD programme, so that the practitioner does not need to be concerned with this issue.
Practical guidance on the cut-off rules can be found in dedicated PCR for building products and technical equipment. Generally speaking, simplified approaches such as EPD may have a 5% cut-off rule in mass or in energy for the corresponding life cycle stage. However, it is generally recommended that the available LCI of the raw materials be accounted for, if available, rather than systematically neglect them to comply exactly with the 5% cut-off. The cut-off rules linked to mass and energy are also limited if the scope of the study is to assess toxicity and ecotoxicity indicators. Some raw materials, such as paints, may have a low energy or mass input while having a high toxicity effect. In this case they should be taken into account in the LCI of the building product. In current PCRs (e.g. the French PCR NF P01-010 standard), these substances are identified – e.g. in France as very toxic (T+), toxic (T), noxious (Xn), or dangerous (N) – and should be included in the inventory if there is an LCI available; otherwise they should be included in the methodological report.
2) Specific guidance for the cut-off rules for complete LCA of buildings
There is a difference in terms of cut-off rules between product LCA and building LCA. For product LCA, the cut-off rules are generally defined in an existing PCR, e.g. EN 15804 (see the ‘Rules from’ section), or in the database. For building LCA studies the practitioner is likely to use already calculated LCA or EPD data. These data have already a cut-off rule linked to the product LCA studies (see the guidance above). At the building level, there is an additional layer of cut-off rules, which correspond to the number of building products quantified to model the full building.
EN 15978 states that the total excluded materials and processes should not exceed 5% of total energy use and mass. However, the cut-off should be used differently between screening, simplified and complete LCAs. The mass of the building is driven mainly by the structural components which can lead some products such as floor coverings being neglected. However, these are likely to have higher environmental impacts than the structural components for some specific impact categories. Therefore the cut-off rules should be extended in complete LCA to account for ILCD provisions.
The provisions in EN 15978 are somewhere in between a simplified and a complete LCA for the cut-off rules aspect.
3) Specific guidance for the cut-off rules for screening and simplified LCA of buildings
For building LCA, it is important to ease the process of doing an LCA study, as it is a time-consuming task to account of possibly hundreds of building products.
In the EeBGuide, the cut-off rules for screening and simplified LCA are less strict than for complete LCA, as some building products or technical equipment may not have LCA or EPD data in some countries.
In the current version of the EeBGuide these may be neglected, owing to potentially missing data, although the general rule for simplification would be to conduct a complete LCA, and then see whether it is relevant to neglect these items (see 2.4 Study types). In any case, the limitation of building products to include should always be justified by the practitioner.
As an alternative for optional building products, it is also recommended that default values be used for these optional building products, as far as possible (see 2.4 Study types), as there are likely to exist in Europe, even if they are not very representative of a specific product. This enables the cut-off rules to be limited, even for screening or simplified LCA (validation step), while easing the completion of the study by practitioners through the use of default values. |