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G-32 (Buildings) / G-30 (Products) Human toxicity and ecotoxicity indicators

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Aspect G-32 (Buildings) / G-30 (Products) Human toxicity and ecotoxicity indicators

Description		 LCIA methodologies usually include midpoint or endpoint indicators for three area of protection: resources, human health and ecosystem. For the two last areas of protection, different indicators are currently available to assess the ecotoxicity and toxicity effects related to a product or a building life cycle. They classify the multimedia fate of chemicals into ecological compartments such as air, water and soil. On the one hand, accounting for toxicity and ecotoxicity effects allows a more comprehensive assessment in terms of the completeness of the set of indicators. On the other hand, these two impact categories are subject to very high uncertainties. Several indicators have been developed by the LCA community, which can lead to different conclusions [Van Caneghem 2010]. Should toxicity and ecotoxicity indicators be used in an LCA of buildings?
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
building products
screening LCA
simplified LCA
complete LCA

Provisions		 Adopt provision of the indicators mentioned in the EN 15804 and EN 15978 standards. These do not include toxicity or ecotoxicity methods, because there is so far no scientifically agreed method available. Yet, if the goal and scope of the study mention the use of an LCIA indicator for toxicity and ecotoxicity, the indicator that is used for the assessment needs to be described.

Rules from
EN 15978 11. Calculation of the environmental indicators
“Note: Indicators for which there is no scientifically agreed calculation method within the context of LCA e.g. human health, ecotoxicity, biodiversity, land use are not included”
ILCD 8 Life cycle impact assessment – calculating LCIA results
Provisions: 8.2 Calculation of LCIA results
ILCD Handbook: Recommendations for life cycle impact assessment in the European context

3.3. Human toxicity
Existing methods for human toxicity aspects that can be used at the midpoint and endpoint level include: USEtox [Rosenbaum 2008] ReCiPe [Huijbregts 2009], IMPACT2002+ [Jolliet 2003] TRACI [Bare 2003], EDIP [Potting 2005], CML 2002 [Huijbregts 2000] and MEEuP [Kemna 2005]

ILCD states that “The use of USEtox as multimedia model, combining chemical fate and exposure with toxicological data, is recommended for midpoint indicators” for human toxicity.

ILCD states that “For the endpoint characterization, it is proposed as an initial basis to apply the most recent values that are proposed by Huijbregts et al. (2005a) using disability adjusted life years (DALYs)”

3.3.5 Discussion on uncertainties and the importance of spatial-temporal differentiation

3.9 Ecotoxicity

Existing methods for ecotoxicity aspects that can be used at the midpoint level include three groups according to their fate modelling:

1. Full multimedia fate modelling: USEtox [Rosenbaum 2008], ReCiPe [Huijbregts 2009], IMPACT2002+ [Jolliet 2003], TRACI [Bare 2003]

2. Partial fate modelling – Environmental key properties: EDIP

3. No fate modelling: Swiss Ecoscarcity [Frischknecht 2008] and MEEuP [Kemna 2005]

ILCD states that “USEtox is preferred as the recommended default method for the midpoint evaluation of freshwater ecotoxicity impacts. This is equally consistent with the model recommended for toxicity impacts for humans. It results from a consensus building effort amongst related modellers and, hence, the underlying principles reflect common and agreed recommendations from these experts.” ILCD states that “No available method is recommended to address marine and terrestrial ecotoxicity.”

Endpoint level for ecotoxicity includes: EPS2000 [Steen 1999], ReCiPe [Huijbregts 2009] and IMPACT 2002+ [Jolliet 2003].

3.9.4 Discussion on uncertainties and the importance of spatial differentiation

Guidance		 The LCA practitioner in the building sector should be aware of the existing and recommended LCIA methods for assessing toxicity and ecotoxicity aspects. Current uncertainties are substantial for these impact categories, although it is generally recognized that it is better to have one indicator than no indicator at all for an impact category. The LCA practitioner in the building sector should also be aware that current efforts are under way at the international level to harmonize the toxicity and ecotoxicity models: see e.g. the USE-oTox model. The latest developments in LCIA for human toxicity have included a new compartment ‘indoor air emissions’ in the USETox model (which is recommended for use by the ILCD). Accounting for indoor air emissions is increasingly relevant, as human beings spend most of their time inside buildings. Such new LCIA developments have to be connected to the EeBGuide aspect of Module B1 ‘Release of dangerous substances to air during the use stage’. The previous European project LoRe-LCA describes the basic concepts of such models in more detail (report available online). Practitioners should also keep in mind that national EPD programmes may also recommend using toxicity indicators that are not included in the core European PCR (EN 15804 and EN 15978). In this case, the practitioner should use them for national LCA studies (if relevant). This guidance will be précised and updated when the EN 15804/EN 15978 are revised.

G-33 (Buildings) / G-31 (Products) Ionizing radiation indicator

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Aspect G-33 (Buildings) / G-31 (Products) Ionizing radiation indicator

Description		 ‘Ionizing radiation’ is an impact category in LCA related to the damage to human health and ecosystems that is linked to the emissions of radionuclides throughout a product or building life cycle. In the building sector, they can be linked to the use of nuclear power in an electricity mix. LCIA methodologies (such as Eco-indicator99, IMPACT 2002+, ReCiPe) currently calculate the ionizing radiation effect of a product’s or a building’s life cycle. Should an ionizing radiation indicator be used in an LCA of buildings?
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
building products
screening LCA
simplified LCA
complete LCA

Provisions		 Adopt provision of the indicators mentioned in EN 15804 and EN 15978 standards. They do not include an ionizing radiation indicator, because so far no scientifically agreed method is available. Yet, if the goal and scope of the study mention the use of an LCIA indicator for ionizing radiation, then the indicator that is used for the assessment needs to be described. As a proxy indicator, EN 15804 and EN 15978 provide a flow indicator for quantifying the radioactive waste (expressed in m3). This indicator should be used, particularly in a national context that relies heavily on nuclear energy, to avoid shifting of burdens (if only the GWP indicator is used).

Rules from
EN 15978 11. Calculation of the environmental indicators
“Note: Indicators describing emission of ionizing radiation and their impact on human health and/or ecosystems in LCA level are intended for consideration during the revision of this European standard.”
ILCD 8 Life cycle impact assessment – calculating LCIA results
Provisions: 8.2 Calculation of LCIA results
ILCD Handbook: Recommendations for life cycle impact assessment in the European context
Existing methods for ionizing radiation that can be used at the midpoint and endpoint levels include [Frischknecht 2000]. ILCD states that “to our knowledge this is the only method that meets the general requirements for a quantitative approach. The fate and exposure model has been based on the ExternE work carried out by Dreicer et al., 1995, who described the routine atmospheric and liquid discharges in the French nuclear fuel cycle. Data from UNSCEAR (1993) were used for three additional radionuclides.”

Guidance		 This guidance will be updated when EN 15804 and EN 15978 are revised.

G-34 (Buildings) / G-32 (Products) Water consumption as a new impact category

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Aspect G-34 (Buildings) / G-32 (Products) Water consumption as a new impact category

Description		 The water consumed during the life cycle of a product or a building can have an impact on the environment. This impact actually depends on the geographical location. For example, in some regions of the world, the same amount of consumed water may have different environmental impacts, depending on the available water resources. The current practice in LCA is that water flows are classified only according to their type (ocean, river, groundwater etc.).

In this context, should a factor for regional availability be included? Should the scarcity of water be considered? What type of water (e.g. drinking water) should be considered? How should water demand be classified regarding its origin?
Study
objective		 ☒ stand-alone LCA ☒ comparative assertion
Study
phase		 ☐
goal and scope definition		 ☐
inventory analysis (LCI)		 ☒
impact assessment (LCIA)		 ☐
interpretation		 ☐
reporting
Relevant for
new buildings
existing buildings
building products
screening LCA
simplified LCA
complete LCA

Provisions		 As there is no commonly agreed method for assessing the impact related to water consumption, scarcity of water is not considered at present. The provisions of EN 15804 and EN 15978 should be used, i.e. use of the indicator ‘net fresh water’. Yet, if the goal and scope of the study mention the use of an LCIA indicator for water consumption, the indicator that is used for the assessment needs to be described.

Rules from:		 EN 15978:
11 Calculation of the environmental indicators
EN 15804:
7.2.3 Parameters describing environmental impacts

ILCD:
8 Life cycle impact assessment – calculating LCIA results
Provisions: 8.2 Calculation of LCIA results
Provisions: 7.4.3.6 Resource elementary flows

Guidance		 1) Practical guidance for the use of EN 15804 indicator

Two cases can be differentiated for guidance: practical calculation of the LCI indicator (currently provided in the CEN TC 350 standards) or available references for the use of a new impact category indicator for water consumption.

– If the ‘net fresh water’ indicator is used according to EN 15804 and EN 15978, it should be calculated as the difference between the water input and water output from a product system. Thus cooling and turbine-use inventory flows are not to be accounted for in the indicator. Salted water is also excluded, as this category deals only with ‘fresh’ water.

2) Practical guidance for the use of a water indicator as a new impact category

If a water indicator is to be considered as an optional impact category, it has to be documented separately. For more information, please consult the following sources. Results from the UNEP/SETAC working group ‘Assessment of Freshwater Use within LCA’ (WULCA) should be considered, and are especially relevant. Scientific papers on the latest developments of the water impact category can also be consulted.

At the standardization level, the ISO is also working on a new standard on water footprint: ISO/CD 14046 Life cycle assessment – Water footprint – Requirements and guidelines.

Revision of this aspect is required if a generally accepted method is available – and used by the EN 15804/15978 standards.

Please also note that some of the EPD programmes consider the inclusion of water in one way or another. Additional information on methodologies can be found in such EPD programmes. However, the various data sources could refer to different methodologies for the calculation of a water indicator.

G-35 (Buildings) / G-33 (Products) Normalization of indicators

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Aspect G-35 (Buildings) / G-33 (Products) Normalization of indicators

Description		 According to the ILCD Handbook, the normalization step refers to the expression of indicators (LCIA, midpoints or endpoints) relative to a common reference by dividing the indicator results by the respective reference value. Different normalization factors can be applied in practice to help the interpretation of results in the building sector.

How can this issue be considered within this guidance document?
Study
objective		 ☒ stand-alone LCA ☒ comparative assertion
Study
phase		 ☐
goal and scope definition		 ☐
inventory analysis (LCI)		 ☐
impact assessment (LCIA)		 ☒
interpretation		 ☐
reporting
Relevant for
new buildings
existing buildings
building products
screening LCA
simplified LCA
complete LCA

Provisions		 The normalization of indicators (which are the LCA results of products and buildings) should remain an optional stage, according to ISO 14044. However, in certain circumstances the normalization of results may be very helpful for the LCA practitioner and/or the decision-maker, and assist interpretation of the study results.

Rules from:		 ILCD:
“Provisions: 6.7 Preparing the basis for the impact assessment […]
Normalisation and weighting: […]
XIII) MAY – Results interpretation: Normalisation and weighting are in addition optional steps under ISO 14044:2006 that are recommended to support the results interpretation (see part 6.3.6)”

“Provisions: 10.3 Three levels of reporting requirements […]
IV) SHALL – Main report, with the following aspects […]

IV.e) Life cycle impact assessment results calculation, where applicable: […]

IV.e.vi) data and indicator results reached prior to any normalization, grouping or weighting shall be made available together with the normalized, grouped or weighted results.

IV.e) Life cycle interpretation: […]

IV.f.iv) full transparency in terms of value choices, rationales and expert judgements.

Guidance		 If the normalization step is considered for product or building LCA case studies it should be carried out in line with the ILCD Handbook. The assumptions should be documented as transparently as possible. Two types of normalization of results can be used in practice, answering two types of objective:

1) Help to identify the most relevant indicators among the global set of indicators

In this case, the LCA results are scaled to a common geographical reference (e.g. at the European level, or in some national contexts) and for a given time period (e.g. 1 year). Generally speaking, normalization factors are available at the world, European and national levels per indicator per year. Doing this will enable the practitioner to identify the key indicators that are driven by the building sector, and in the specific study. It is a way to identify hotspots, and reduce for example the number of indicators from EN 15804/EN 15978 or other indicators available in the ILCD Handbook (if relevant). The main issue is to be able to obtain the normalization factors for each indicator. The LCIA method usually provides normalization factors for the midpoint, such as the global warming potential (GWP), or endpoint indicators.

For example, the CML 2002 method provides normalization factors for The Netherlands (1997), Western Europe (1995) and the world (1995). Other impact assessment methods, such as Eco-indicator 99, IMPACT 2002 and ReCiPe, also provide normalization values.

Some of these LCIA methods may be used in a building LCA in addition to the baseline indicators given in the EN 15978/EN 15804 standards. Previous European projects have provided the values for these normalization factors through their online deliverables.

Examples of normalization factors that can be used for the French context (mean impacts per person and per year) can be found below:

Mid-point indicators Unit equiv-person /year Source
GWP kg eq-CO2 8680 CITEPA
AP kg eq-SO2 62.3 CITEPA
POCP kg eq-C2H4 19.7 CITEPA
EP kg eq-PO43- 38.1 IFEN
Other indicators Unit eq-person Source
Primary energy demand MJ 48 670 Observatoire de l’énergie
Water consumption m3 339 IFEN
Radioactive waste dm3 0.51 ANDRA
Other wastes kg-eq 10400 ADEME

[Peuportier 2008]

Example of normalization factors that can be used for the European context can be found in the BRE Environmental Profiles Methodology.

A comprehensive set of normalization factors are described in detail in LoRe-LCA.

2) Comparison of LCA results with existing benchmarks

In the building sector, practitioners may be asked to comply with a set of targets for overall environmental performance. For example, an architect or a real estate manager may need to answer the following question: “Does the studied building perform well compared with current best and good practice?” In this particular case, the LCA results can be normalized to existing reference values to compare design alternatives with current practice.

Appendix B provides some first reference values for buildings for Germany and France.

G-36 (Buildings) / G-34 (Products) Weighting of indicators

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Aspect G-36 (Buildings) / G-34 (Products) Weighting of indicators

Description		 According to the ILCD Handbook, the weighting step refers to an optional step of the ISO 14044 standard to support the interpretation of the profile as a fully aggregated result. Generally speaking, it is a subsequent step to the normalization of indicators (see aspect ‘normalization’), where each normalized indicator is multiplied by a specific weighting factor that is intended to reflect the relative importance of the various impact categories. Different weighting methods can be applied in practice to help the interpretation of results in the building sector.

How can this issue be considered within this guidance document?
Study
objective		 ☒ stand-alone LCA ☐ comparative assertion
Study
phase		 ☐
goal and scope definition		 ☐
inventory analysis (LCI)		 ☐
impact assessment (LCIA)		 ☒
interpretation		 ☐
reporting
Relevant for
new buildings
existing buildings
building products
screening LCA
simplified LCA
complete LCA

Provisions		 The weighting of normalized indicators (which are the LCA results of products and buildings) remains an optional stage in this guidance document, in accordance with ISO 14044. However, in certain circumstances the weighting of indicators may be asked for by the decision-maker in order to ease the interpretation stage.

Rules from:		 EN 15978:
11. Calculation of the environmental indicators
“The standard does not present any methodology for the aggregation of the individual indicators.”

ILCD:
“Provisions: 6.7 Preparing the basis for the impact assessment […]
Normalization and weighting: […]
XIII) MAY – Results interpretation: Normalisation and weighting are in addition optional steps under ISO 14044:2006 that are recommended to support the results interpretation (see part 6.3.6)”

“Provisions: 10.3 Three levels of reporting requirements […]
IV) SHALL – Main report, with the following aspects […]

IV.e) Life cycle impact assessment results calculation, where applicable: […]

IV.e.vi) data and indicator results reached prior to any normalization, grouping or weighting shall be made available together with the normalized, grouped or weighted results.

IV.e) Life cycle interpretation: […]

IV.f.iv) full transparency in terms of value choices, rationales and expert judgements

Guidance		 If weighting is chosen in the case study, this should be carried out with regard to the ILCD Handbook. The LCA practitioner should keep in mind that the weighting step in LCA is always a subjective step, which should be documented as transparently as possible. The LCA practitioner should not use weighting indicators in comparative assertions; and, whenever such indicators are used, should include a statement that ‘It should be recognized that there is no scientific basis for reducing LCA results to a single overall score or number.’

In practice, different approaches can be used to weight the indicators.

– The first approaches are typically already included in final LCIA methods that are used by LCA practitioners. For example, weighting factors used in the LCIA methods (such as Eco-indicator 99, IMPACT 2002+ and ReCiPe) to go from midpoint to endpoint indicators (reflecting three areas of protection: human health, ecosystem and resources) may be based on different assumptions. For example, the developers of the Eco-indicator 99 method, as well as ReCiPe, used the cultural perspective based on [Hofstetter 1998] to adapt the weighting factors, i.e. egalitarian, hierarchical and individualistic perspectives. Thus the midpoint categories, e.g. for the area of protection of human health (such as carcinogenic, respiratory effects, climate change, radiation and ozone depletion) are weighted differently according to each perspective. In the LCA of buildings, the practitioner should be cautious when using a damage indicator (if relevant for the study), as it is based on a series of assumptions.

– The second approach uses expert panels. They are defined within an LCA study, and this should be done on a case-by-case basis. Different mechanisms can be used, such as setting the weighting factors by public policymakers or industry panels, broad stakeholder panels, expert panels, and so on [ILCD 2011a]. Examples of weighting in the LCA and construction sector can be found for the European context in the BRE Environmental Profiles Methodology, for example. Other weighting methods are also implemented in some building LCA tools, such as EcoEffect in Sweden.

A comprehensive list of weighting methods is described in detail in the LoRe-LCA project.

G-37 (Buildings) / G-35 (Products) Uncertainty analysis for comparative assertion

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Aspect G-37 (Buildings) / G-35 (Products) Uncertainty analysis for comparative assertion

Description		 An uncertainty analysis measures the variability of the data values: for example, a low variance leads to a high precision. Because of the long supply chain of building products and buildings as a whole, uncertainties are aggregated over the life cycle. Following [Huijbregts 2001], different types of uncertainty can be found in LCA: parameter uncertainty, model uncertainty, uncertainty due to choices, spatial variability, temporal variability, and variability between the sources and the objects. In general, an uncertainty analysis should not be confused with a data quality assessment. Similarly, an uncertainty analysis for a stand-alone LCA should not be confused with an uncertainty analysis for a comparative assertion: in the first case, all the various types of uncertainty mentioned above are present, whereas in the second case, not all of them are present. In a comparative assertion supporting decision-making, it is important only to ensure that the LCA results remain robust, even if the absolute LCA is uncertain. This is especially true when the differences between two alternatives are less than 20% (a percentage often used by LCA practitioners as the level below which it cannot be stated that A is better than B).

In this context, when and how should an uncertainty analysis be performed for comparative assertion in the building sector?
Study
objective		 ☐ stand-alone LCA ☒ comparative assertion
Study
phase		 ☐
goal and scope definition		 ☐
inventory analysis (LCI)		 ☐
impact assessment (LCIA)		 ☒
interpretation		 ☐
reporting
Relevant for
new buildings
existing buildings
building products
screening LCA
simplified LCA
complete LCA

Provisions		 An uncertainty analysis should be conducted for comparative assertions, and should be considered during the review process. It may be addressed by scenario analyses. For extended studies and in-depth discussions of uncertainty, the rules of the ILCD Handbook should be used. Also, the ongoing scientific discussion may be taken into consideration.

Rules from:		 ILCD:
Provisions: 6.5.4 LCI modelling provisions for Situations A, B, and C
I.a.vi) Comparative studies, scenarios, uncertainty calculation:
“Uncertainty calculation shall be performed [for comparative studies], unless it has already been used to derive the reasonably best and worst case scenarios.”
“It is recommended to also perform and report such assumption scenarios and uncertainty calculations for non-comparative LCI and LCA studies.”
ANNEX E: Addressing Uncertainties in LCA
16.3 Aggregating uncertainties over the life cycle

“Three main sources of uncertainty have been addressed: stochastic uncertainty, choice uncertainty, lack of knowledge of the studied system”

The ILCD Handbook also provides rules for not mixing the data quality aspects (falling under the term ‘accuracy’) with the other concept of ‘precision’ (or ‘uncertainty’). The graphical illustration in Figure 13 demonstrates this point.

Figure 15: Concept of precision

Guidance		 1) General guidance for product and building LCA studies

The main difference between LCA studies with comparative assertions and stand-alone LCA studies lies in the fact that some parameters or assumptions are the same in both cases (also called ‘conventional parameters’) so that the number of uncertainty sources may be considerably reduced. In this case, the practitioner should check only whether the LCA results remain robust even if the stand-alone LCA is uncertain on several parameters (e.g. epistemic such as the linear relations between flows, processes and impacts; the life expectancy of a building etc.).

Another problem for the LCA practitioner lies in selecting an adequate method to assess the uncertainty. Various quantitative methods exist in the literature to assess uncertainties, such as Monte Carlo simulation, for example. Other methods, such as fuzzy logic and statistical Bayesian methods, have been developed and applied to LCA by researchers.

However, most of these sophisticated numerical methods are currently not implemented in user-friendly LCA software for buildings, so the practitioner typically cannot easily use them.

Based on the state of the art of building LCA tools, the best way to conduct an uncertainty analysis is to carry out scenario analyses that assess the most significant parameters of the LCA study. It is then possible to check whether one alternative still remains better than another in the various scenario analyses. The main issue is to identify the parameters, and to define their ranges of variation.

More information on scenarios for LCA in construction can be found in a previous report of the LoRe-LCA European project (FP7), available online.

2) Specific guidance for advanced building LCA studies

LCA may often be used as a decision-making tool to support a comparison of alternatives, e.g. during the building design stage. In this case, it is relevant to have guidelines on how to assess whether the choice of the best alternative from an LCA point of view is robust when using uncertain aspects of the building LCA model. Different steps may be conducted for a detailed analysis:

– Identification and quantification of uncertainties for the key parameters

Uncertainty sources for building LCA studies can be found for the various contributors:

– building products: the LCA data of the building materials, the reference service life of the building products, the quantity take-off;
– energy consumption: the LCA data of the energy processes, value taken from thermal simulation software;
– water consumption: the LCA data of the water processes and treatment, the value determined with a calculation tool.

In addition, uncertainty can be found in the methodological choices made by the practitioner within the LCA software (data used, calculation rules etc.)

These sources of uncertainty may be assessed by defining distribution curves (e.g. log-normal, normal, triangle, Weibull) and then by deriving the relevant statistical parameters (e.g. the confidence interval at 95% or other statistical parameters if relevant).

This may provide relevant information for building LCA practitioners: for example, for a building product, the share of uncertainties linked to the reference service life (RSL), the LCA data or the quantity take-off (if these three sources of uncertainty are relevant for the study). A similar approach can be applied to the operational energy and water impact values.

– Propagation of uncertainties in building LCA results

For a building case study, the relative share of impacts driven by building products, operational energy or water use, etc. can be identified and the corresponding uncertainties assessed.

This approach allows building LCA results to be presented with e.g. a mean value and a standard deviation (as e.g. 10 kg eq-CO2/m²/yr ±1.4 for the GWP indicator of a building).

This is the first step in identifying the sources of uncertainty in building LCA results. If relevant, these uncertainties can be reduced, e.g. by collecting more accurate/precise data.

– Use of distribution curves for the key parameters in comparative assertions

The uncertainties for the key parameters can then be used in a comparative assertion for two building case studies (fulfilling the ISO 14044, ILCD and EeBGuide requirements, e.g. the two buildings shall have the same functional equivalent). This allows the practitioner to assess whether alternative A is better than B when taking uncertainties into account. If the standard deviations of alternatives A and B do not overlap, then the comparative LCA results can be considered robust. If they do overlap, it is not possible to state that A is better than B, given the corresponding uncertainties.

G-38 (Buildings) / G-36 (Products) Sensitivity analysis

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Aspect G-38 (Buildings) / G-36 (Products) Sensitivity analysis

Description		 According to the ILCD Handbook, the goal of a sensitivity analysis is to assess the reliability of the study by adjusting the main parameters to see how this affects the final results. It is part of the interpretation step, and is generally used together with complementary approaches, such as scenario or uncertainty analyses. Sensitivity analysis can be an effective way of predicting the outcome and the impact of a variable on the result. By conducting it, it is possible to make statements with regard to data quality and precision.

Within this guidance document, is a sensitivity analysis necessary? How and when can it be conducted, depending on the study type?
Study
objective		 ☒ stand-alone LCA ☒ comparative assertion
Study
phase		 ☐
goal and scope definition		 ☐
inventory analysis (LCI)		 ☐
impact assessment (LCIA)		 ☒
interpretation		 ☐
reporting
Relevant for
new buildings
existing buildings
building products
screening LCA
simplified LCA
complete LCA

Provisions		 A sensitivity analysis should be conducted for LCA studies that include comparative assertions. It may be used for a stand-alone LCA (if relevant to the goal and scope of the study).

Rules from:		 EN 15978:
10.3 Data quality
The significance of the data chosen for the building LCA shall be assessed by means of sensitivity analysis (more information in section 10.3 Data quality of the standard)

ILCD:
Provisions: 9.3.3 Sensitivity check (of accuracy and precision)
ILCD states that “it is useful to structure the sensitivity check along the LCA stages.” The sensitivity of results should be checked in order to improve the quality and the validity of the study. The main goals are:

– sensitivity to significant issues (e.g. LCI flows, LCIA factors, modelling choices and assumptions);
– improvement of robustness of sensitive issues data, parameters, methodological choices;
– report final achievements; potentially revise the goal and scope.

Guidance		 Sensitivity analysis can be considered as an alternative method for assessing the uncertainty in comparative assertions. It is very similar to scenario analysis, as the main focus is to set a range of variation for a given number of parameters of the LCA study.

Sensitivity analysis can be conducted for a stand-alone LCA to assess the range of variation of the LCA results. More frequently, it is used to improve the robustness of decision-making. In comparative LCA studies it enables the user to assess whether alternative X remains better than alternative Y when subject to a modification of the LCA modelling parameters or methodological choices (e.g. burden allocated or not to a by-product).

The different aspects to consider for the sensitivity analyses depend on the goal and scope of the study.

1) Guidance for building LCA studies

For example, the usual parameters for building LCA, such as the reference study period of the building (RSP), the end-of-life (EoL) scenarios, the transportation distances, the choice of data for building products, energy and water processes (generic, specific) can be submitted to a sensitivity analysis (if relevant to the goal and scope of the study, and if the LCA tool allows such an analysis). For more information about sensitivity analysis guidelines for building LCA, please consult the LoRe-LCA report ‘Methods and guidelines for sensitivity analysis, including results for analysis on case studies’, available online.

2) Guidance for product LCA studies

For product LCA, the sensitivity analysis can be conducted for the choice of data (e.g. generic vs. specific data for the foreground system), the EoL scenarios, the transportation distances for the upstream processes (e.g. raw materials supply) etc.

G-39 (Buildings) / G-37 (Products) Scenario analysis

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Aspect G-39 (Buildings) / G-37 (Products) Scenario analysis

Description		 Scenario analyses usually refer to future conditions that cannot be fully known by the time the LCA study is conducted. However, the uses of scenarios can meet different goals. Scenarios can look backwards or forwards, and can be linked to different applications. For example, a product is likely to be handled differently in each building. In this context, the use of scenarios may be very helpful in providing complementary results.

Within this guidance document, is a scenario analysis necessary? How and when can it be conducted, depending on the study type?
Study
objective		 ☒ stand-alone LCA ☒ comparative assertion
Study
phase		 ☐
goal and scope definition		 ☐
inventory analysis (LCI)		 ☐
impact assessment (LCIA)		 ☐
interpretation		 ☒
reporting
Relevant for
new buildings
existing buildings
building products
screening LCA
simplified LCA
complete LCA

Provisions		 Scenario analyses may be conducted if relevant for the goal and scope of the study. They should be conducted for individual assumptions and choices in order to explain the impacts of such choices. For these cases, a scenario analysis should be conducted against the baseline scenario (see Chapter 2).

Rules from:		 EN 15804:
7.3 Scenarios and technical information

ILCD:
Provisions: 9.3.3 Sensitivity check (of accuracy and precision)

Guidance		 A scenario is addressed for each life cycle stage in EN 15804 and EN 15978. However, in addition to the chosen scenario for each life cycle stage it may be useful to assess alternative scenarios.

A scenario analysis is closely related to a sensitivity analysis for key parameters. For example, in a scenario analysis, the practitioner may need to look at different building alternatives or reference study periods. The different aspects to consider for the scenario analysis depend on the goal and scope of the study. For example, the scenario analysis can be predictive (forecast, what-if), explorative (external or strategic) or normative (preserving or transforming) [LoRe-LCA 2011].

1) Guidance for building LCA studies

Different aspects can be considered for a scenario analysis, such as the reference study period of a building, the service life of building products, renovation scenarios, energy demand during the use phase, and user behaviour. For more information about scenario analyses for building LCA, please consult the LoRe-LCA report ‘Report on scenario for LCA in constructions’, available online.

2) Guidance for product LCA studies

For product LCA, scenario analysis can be done e.g. for an EPD that is likely to have different impacts in the implementation and use phases. Examples of such products include floor coverings. Having different scenarios enables the building practitioner to select the more appropriate scenarios for the building LCA case study.

3) Specific guidance in EeBGuide reporting templates

Scenario analyses are part of the reporting template for products and buildings case studies. In addition to the baseline scenario, the LCA practitioner is invited to conduct scenario analysis on a relevant set of parameters.