2.4.1 Screening LCA

Purpose

A screening LCA study may serve for an initial (quick) overview of the environmental impacts of a building or a product. The challenge is to adapt the LCA methodology and simplify the use of LCA at the early design stage. With a screening LCA, it is not possible to retrieve detailed results on the environmental performance of a building or a product, and comparative assertions according to ISO 14044 cannot be based on it. Comparisons can be made internally, but these comparisons should not be published. This type of study yields an estimate of the environmental performance, which can be helpful in the early stages of design (e.g. for an architect’s draft design0 in of a research project (e.g. to identify environmental hotspots that require an additional, in-depth assessment).

Completeness of assessment

A screening study would typically focus on the main contributors to the system under assessment, including (but not limited to) the input materials, water and energy use, and the transportation of users (if relevant). In screening LCA, to avoid misleading results, care is needed to ensure that omitted building products are not significant for the chosen environmental indicators. It is also important to use adapted calculation rules for screening LCA (e.g. the use of statistical data for assessing impacts of water consumption). More information on the calculation rules can be found in Table 5.

Cut-off rules, as specified in EN 15978 and EN 15804, and in the ILCD Handbook, may not apply to screening LCA studies for buildings or products. For example, in the early design stages not all the input raw materials and components are known in detail, which means that some of them are omitted. Rather than systematically neglect them, one option is to try to model these omitted processes using default values. Generally speaking, life cycle modules, inputs and services should be omitted only if their insignificance for the corresponding environmental indicator can be scientifically justified.

A screening study might focus on one single indicator or several, and most studies should include PENRT (total use of non-renewable primary energy resources) and if relevant the GWP (global warming potential) and PERT (total use of renewable primary energy resources). As a general rule, a set of between five and seven additional relevant core LCIA indicators can be used (see the corresponding aspect in section 5). They may be taken from either EN 15804 or EN 15978, and from additional indicators described in the ILCD Handbook (if relevant for the purpose of the study).

Data representativeness

In comparison with the other study types, a screening study is likely to be based on generic assumptions, according to the goal and scope of the study. For example, if the goal is to conduct an LCA study within a European project, then the use of generic assumptions for the EU context may be sufficient. However, if the goal is (as in most cases) to conduct an LCA study that is representative within a national context, then generic assumptions for the national context are appropriate. Five major areas related to the representativeness of data can be considered: geography, technology, age, time and precision. It is also important to ensure consistency within the data used.

Geography

The data used in a screening study should, as far as is practical, given the existing time and budget constraints, relate to the country from which the building or product originates, and in which it is built or produced. However, as this is not always possible, it is also acceptable to use assumptions from a neighbouring country (with a similar context), or average European data, or even average global data. In this case, the data used, and their limitations, should be highlighted in the documentation. These provisions do not apply to data on energy, water and waste treatment processes, as national data are preferable (e.g. electricity mix, natural gas) but, otherwise, European data can be used if relevant.

Technology

The data used should represent the technology used as closely as possible. For example, if different heating systems are to be assessed from a product or building perspective, or if a comparison of bearing structures from reinforced concrete against timber framing is intended, then the data should reflect an equivalent state-of-the-art technology.

Precision

Average environmental quantitative information on the building or product may be taken from generic LCA data, or from default values for major components. For other sources of impacts related to the operational energy and water, and to the construction site, refer to the provisions given in the guidance document.

Consistency

A qualitative assessment of whether the LCA methodology is applied uniformly to the various components and processes should be made in relation to the goal and scope of the study.

Documentation

Use the reporting template provided. The minimum requirements for items reported on can be summarized as follows:

  • Definition of the goal and scope
  • Life cycle stages included
  • Main input materials/items included, as well as processes for energy, water etc.
  • Overview of calculation rules, and comment on degree of approximation/uncertainties
  • Impact categories considered
  • Life cycle impact results and interpretation (conclusions)
  • Statement regarding consistency
  • Results

Communication of LCA report and results

Screening LCAs are for internal communication purposes only (e.g. during an architectural competition), not public comparative purposes. A statement about the uncertainty of the results due to the screening process must be included.

Examples of screening LCAs:

  • Building LCA study to identify environmental optimization potentials in the early design stages (for an architect or stakeholder, helping to improve the building design).
  • Supporting documentation for an architectural competition.
  • Comparison of a, innovative new product and an existing one (e.g. within a company).

2     Methodological approach of the EeBGuide.


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