G-02 Classifying the decision context as situation A, B, and C for building and product LCA

Aspect G-02 Classifying the decision context as situation A, B, and C for building and product LCA
The ILCD Handbook distinguishes between different decision contexts for LCA studies. This distinction is part of the goal and scope definition of an LCA study, and has major implications for further definitions of system boundaries and modelling principles, etc. According to the ILCD Handbook, situation A modelling is defined as ‘micro-level decision support’, whereas situation B is characterized as ‘meso- and macro-level strategic (‘policy’) decision support’. Thus situation A refers primarily to product- or process-related decision support studies, whereas situation B applies to strategic decision support studies. It is important for practitioners, to understand under which situation an LCA study has to be established. In addition, the differentiation of when to use situation A or situation B might be unclear in the building sector.

Related study objective

stand-alone LCA comparative assertion

Related study phase

goal and scope definition inventory analysis (LCI) impact assessment (LCIA) interpretation reporting

Relevant for

new buildings existing buildings construction products screening LCA simplified LCA complete LCA
Provisions Situation A (attributional LCA) should be used for individual product or building LCA studies that do not have a major influence on the background system (such as the energy supply).Situation B (consequential LCA) should be used in modelling specific cases where macroeconomic systems are significantly affected through the use and the dimension of the assessed technology. If an LCA study is believed to be related to situation B, the ILCD Handbook and LCA literature should be consulted for guidance on how to proceed.
Rules from:


5.3 Classifying the decision context as Situation A, B, or C

Table 7: Combination of two main aspects of the decision context: decision oriented and type of consequences in background system or other systems [ILBD 2010a]

Provisions: 5.3 Classifying the decision context

Provisions: 6.5.4 LCI modelling provisions for Situations A B, and C


Some examples of situation A, B and C modelling are mentioned in the ILCD Handbook.

Situation A refers to single product assessments that will not change the background system (e.g. when it refers to a limited share of the total production of an industrial sector). The most relevant application of situation A (micro-level decision support) are:

  • ecodesign/simplified LCA;
  • development of specific, average, generic unit process or LCI results for the identified intended applications under situation A;
  • development of Product Category Rules;
  • development of a life-cycle-based Type III environmental declaration (EPD) for a specific good.

Situation B refers to life-cycle-based decision support that will have consequences outside the analysed system boundaries via market mechanism changes. The most relevant applications of situation B (meso/macro-level decision support) are:

  • policy development (e.g. spreading renewable energy technologies or not; forecasting unconventional technology development in the future);
  • policy information (e.g. identifying product groups with the largest environmental improvement;);
  • development of specific, average, generic unit process or LCI results for the intended applications identified under situation B.


For unclear situations, the ILCD Handbook gives the following advice:

“In this situation, the guiding criteria shall be whether the consequences of the analyzed decision alone are big enough to overcome related thresholds and/or other constraints and result in large-scale consequences in the installed production capacity outside the foreground system. Then: Situation B. If not: Situation A.”

The last option is to use situation C “Accounting” if the LCA is not intended to be used as for decision support. Situation C1 (“including interactions with other systems”) is distinguished from situation C2 (“excluding interactions with other systems”). “The most relevant applications are e.g. for C1:

  • Monitoring of environmental impacts of a nation, industry sector (only for situation C1);
  • Policy information (identifying product groups with the largest environmental impact);
  • Corporate or site environmental reporting”
Most of the LCA studies published in the building sector have used the LCA approach called attributional modelling (or situation A in ILCD). This type of modelling is the most familiar to the LCA practitioner. Alternative modelling choices are available, especially consequential modelling (or situation B in ILCD). This modelling approach assesses the consequences of the introduction of a new technology or new processes by looking at the marginal effects. The questions addressed are different in these two modelling approaches.An attributional LCA assesses the environmental impact of one quantity unit or one piece of a product. Any scaling-up of the environmental impacts of this product is linear. This means that the environmental and technical consequences (and possibly also the economic consequences) of the life cycle of the assessed system are seen not to have significant impacts on other technical systems, products, etc. This is often seen as a feasible simplification in the process of modelling parts of the real world.A consequential LCA, by contrast, assesses the environmental impacts of products or technologies with consideration of the indirect effects, i.e. by assessing the consequences of the assessed life cycle on other systems. As an example, the assessment of biofuel might include the consequences of increased pressure for the available land in tropical forests due to energy crop harvesting, or include the assessment of consequences of a shift of technologies due to the reduced availability of one rare earth.

Conducting a consequential LCA may result in special requirements for LCA background data, and typically increases the options or choices within the assessed system. As a consequence, the LCA practitioner is required to make an increased number of assumptions, which may reduce the significance of a result.

The European standards EN 15804 and EN 15978 do not consider consequential LCA. It may be valid for specific cases to conduct a consequential LCA, but for the most common applications of LCA in the building and construction sector an attributional LCA should be the method of choice. If a consequential LCA is conducted, the LCA practitioner needs to fully understand the related methodologies, and therefore make him or herself thoroughly familiar with the corresponding literature.

1) Guidance for the choice between attributional and consequential LCA in the building sector

The practitioner should use attributional LCA (situation A in the ILCD Handbook) for the following applications:

  • development of PCR or EPD of building products and technical equipment;
  • LCA used for ecodesign of an individual product or building.

The practitioner may use consequential LCA (situation B in the ILCD Handbook) for the following applications:

  • building sector policy development (e.g. assessment of the marginal effects of a widespread development of renewable energies or new technologies for products; orientation of new environmental regulations).

Situation C is unclear in the ILCD Handbook, as it is intended not to have a decision support. However, even an internal LCA study in a company always has support, such as benchmarking, or improvement potentials. Generally speaking, most of the time the LCA practitioner in the building sector will rely on situations A or B.

Whereas a single product or building does not change the background system very much (situation A), this will no longer be the case when all the building sector is considered. For example, in France, where many buildings are heating by using electricity, this leads to a winter peak demand when thermal power plants are turned on, resulting in increased CO2 emissions [Peuportier 2008]. Assessing the entire building stock should relate to a situation B decision context. Under the specific goal and scope, situation B may be used for individual systems that are large enough to potentially influence the background system.

2) Guidance for studies complying with goal and scope definition according to EN 15804/EN 15978

EN 15978 and EN 15804 relate solely to attributional LCA studies. As a result, provisions and guidance that are in line with these standards in terms of scope definition and inventory analysis refer only to situation A (attributional modelling) in the EeBGuide.

3) Specific guidance and current limits for consequential LCA

The use of situation B needs appropriate LCI data. Usually, the practitioner may rely on background databases (providing consequential datasets). The practitioner can refer to the provision ‘6.5.4 LCI modelling for Situations A, B, and C’ for more guidance and rules.

In the LCA community, there is no commonly agreed understanding on how to decide which type of decision context situation should be applied. This is especially true for medium-scale systems (e.g. a neighbourhood or a district) for which no strict recommendations are given in the ILCD Handbook. In these cases, the use of a situation A or B should be justified by providing evidence e.g. on the possible modifications on the background system.

As the distinction between attributional and consequential LCA is currently a much-discussed topic, the practitioner may also be interested in referring to the recent review articles published by [Frischknecht 2010], [Earles 2011] and [Zamagni 2012]. According to [Zamagni 2012] there are still several issues to address in consequential LCA, including the selection of appropriate data, the identification of market mechanisms, and the affected processes that should be included in the system boundaries. The authors state that scenario modelling can be a useful approach in dealing with present mechanisms and future developments. Scenarios can be predictive (what will happen?), explorative (what can happen?), or normative (how can a specific target be reached?).

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