When conducting an LCA study, the practitioner is constantly confronted with figures: some are needed to specify a modelling parameter; others are needed as cross-references, or benchmarks for comparison purposes. Such numbers always depend on the context of a study, and are generally not globally valid, which is why this guidance does not specify the use of predefined default values.

For numerous studies, however, average or default values may be helpful, and have the potential to significantly reduce the effort for data collection, especially if the relevant figures are required, yet are not critical for the study outcome. Also, to gain confidence in one’s study, the practitioner may use such values for cross-reference. For such purposes, a non-comprehensive collection of various default values is provided in this Annex. This collection of values does not claim to be ultimately right, and the practitioner has to decide by himself or herself whether the given values are applicable to the study’s context, and whether utilizing these values will be beneficial for the study.

Default Parameters for Building LCA

Default Values – Buildings

Back to EeBGuide Guidance Document Part B: BUILDINGS

Following a simplified understanding of a building’s life cycle, the reference study period can be seen as the timespan of use, i.e. the duration of services within Module B. Hence the reference study period has a significant impact on the use stage’s contribution to the life cycle impacts. This means that the reference study period influences the relation of impacts from the different life cycle stages, and thus may cause different conclusions to be drawn regarding the importance of a life cycle stage.

The following table provides definitions for reference study periods from various sources. These definitions are not based on scientifically proved lifetimes, but usually reflect a consensus, e.g. within one country.

Other default values

For referencing purposes, typical LCA results may be helpful. These values are typically heavily dependent on the assumptions made, and on the various rules that have been applied to a study. Hence a comparison with such values has to be made with special care.

Germany: DGNB

In Germany, the DGNB building labelling system defines benchmarks for the ‘physical part of the building’, i.e. the combination of building construction (Modules A1–A3), maintenance and refurbishment (Modules B2–B5) and the end of life (Modules C and D). All DGNB rules and provisions (e.g. reference study period) apply to allow for a justified comparison.

France: HQE Performance

The following tables present the results of a French pilot project, called HQE Performance, concerning the LCA of 74 low-energy buildings. The building LCA tool ELODIE has been used to perform the life cycle assessment of every case study. Results are presented as mean values calculated for the construction of new buildings for a 50-year reference study period.
The following building types are considered:

• detached houses;
• multi-residential buildings;
• office buildings

Reference values are detailed for the following building impact sources:

• equipment, products and materials (from cradle to grave, i.e. Modules A, B, C);
• operational water consumption (Module B7);
• operational energy consumption (thermal regulation uses, Module B6);
• operational energy consumption (other uses, Module B6).

Reference values for new buildings

Note: The four indicators considered (non-renewable primary energy, global warming potential, inert waste and water consumption) are calculated according to the rules given in the French XP P01-020-3 and NF P01-010 standards.

This document yields several distinctions that are relevant for the further procedure to compile an LCA study. The distinctions are given in the decision tree showed in Figure 5.

In the first step, both for a building LCA and a product LCA, the decision on the scope of the study has to be made. This leads to the definition of the study type used and the relevant aspects to assess may be filtered accordingly for the next steps. This includes the identification of life cycle stages that should be assessed and those that will remain optional. Refer to Table 3 for the identification of mandatory and optional life cycle stages.

On the basis of the study type chosen and the life cycle stages of concern, the remaining relevant aspects are then taken into account during the setup of the LCA building model and for defining individual parameters of the system.

As the term “energy efficiency” implies a lower energy input into a building or building service through a more advantageous benefit/input ratio, a comparison of the situation with or without the technology concerned may be required to identify the actual environmental consequences of utilizing such a technology. It needs to be noted that the careful definition of the two situations and a comprehensive life cycle view (inclusion of all relevant life cycle stages) is necessary to cover all environmental consequences. In addition, comparison should be done on the basis of a common functional equivalent (i.e. a representation of the required technical characteristics and functionalities of the building).

2     How to use this Guidance document

• 2.1.    Scope of this Guidance.
• 2.2.    Structure of the Guidance document.
• 2.3.    Study types.
• 2.3.1.    Screening LCA.
• 2.3.2.    Simplified LCA.
• 2.3.3.    Complete LCA.
• 2.3.4.    Summary of the study type definitions.
• 2.4.    How to conduct an LCA study within the field of Energy efficient Buildings.
• 2.4.1.    How to commence and proceed with an LCA study.
• 2.4.2.    LCA study setup: Generic template.
• 2.4.3.    Use of a baseline scenario.
• 2.5.    Compliance with this Guidance.
• 2.6.    LCA studies within research projects of the Energy efficient Building European Initiative (E2B EI).
• 2.7.    An introduction to service life planning.
• 2.8.   Further information and training materials.

Back to EeBGuide Guidance Document Part B: BUILDINGS

After the selection of the study type and the subsequent filtering of aspects, the LCA study is set up according to the general LCA practice as resulting from applying ISO 14040/14044. This process is briefly explained with a generic template of how to set up an LCA study. The individual steps are numbered – note that this numbering does not relate to any study or other procedure that is defined elsewhere.

Step 1 – Goal and Scope definition

The definition of goal and scope mainly relates to the identification of study type and aspects considered for the LCA study as described in section 2.4.1. Based on the definition of reasons for carrying out the study as well as its intended application and audience, further specifications have to be made, e.g.:

• Object of assessment (e.g. building or innovative technology) and its function (e.g. office use or energy producing façade collector)
• Set up of a functional equivalent – special especially important for comparative assertions
• System boundaries – specifications on life cycle phases to be included (e.g. for existing buildings) depending on the study type or hints for applying cut-off rules (e.g. with regard to infrastructure and transport) are specified
• Procedure for allocation – several common allocation cases (e.g. for co-production or reuse and recycling) with regard to mass, energy or environmental significance are provided
• Choice of environmental impact categories, indicators and characterization models used for the impact assessment
• Data requirements and quality – the type of data to be used (e.g. generic or specific), data uncertainty, the use of foreground or background data (e.g. power-mix) and specific requirements on data quality for comparative assertions are defined; missing data have to be documented
• Assumptions and limitations – may address e.g. the setup of specific scenarios for the use phase, the treatment of capital equipment or machinery within the production phase, or deviations from guidance provided within this document; a transparent documentation is required

Examples and guidance on the mentioned topics are provided within respective aspects of the chapters for “Goal and Scope definition”.

Step 2 – Inventory Analysis and Product Model

The way of data collection as well as the quantification of input and output flows (e.g. materials or energy) differs for screening, simplified and complete LCA studies and depends on the level of separating single elements for the object of assessment as well as the assessed life cycle stages . Data sources (e.g. public available or company/product specific ones) used and the quality of background data for the inventory analysis have an influence on the impact assessment. Guidance on data collection, calculation, validation and relating the information to e.g. life cycle stages or elements of the object of assessment is provided within the chapters for “Life cycle inventory analysis”. Furthermore, building and building product contributors are defined which have to be considered.

Step 3 – Impact Assessment

For the quantification of potential environmental impacts, the choice of environmentally relevant, technical and scientifically valid environmental indicators as well as the underlying characterization models for impact assessment, is of importance. Environmental indicators and impact categories where scientific consensus is not yet reached so far (e.g. water consumption, land use change or carbon sequestration) are addressed within the chapters for “Life Cycle Impact Assessment”.

Step 4 – Interpretation and Documentation

The interpretation of results serves e.g. for identifying hot spots (e.g. distinct life cycle phases or elements of the object of assessment contributing to environmental impacts) or understanding sensitivity and uncertainty of results through respective analysis. Requirements and guidance on the use of normalization, grouping or weighting are provided within the chapters for “Interpretation”. Cases, where a sensitivity analysis is useful, are defined as well.

Reporting templates are provided online at the official project website (https://www.generis-solution.eu/) and assist especially in conducting step 1. These templates form the basis for a documentation which is in-line with the present guidance document and which might be enhanced with further specific information, if required or recommended (e.g. if future technologies and innovations are regarded at).

Step 5 – Review

An external critical review is necessary for all comparative LCA studies or studies which are made public available. Guidance on simplifications for the review of stand-alone or screening LCA studies or studies within the E2B EI is provided under section “Reporting” within chapter “General aspects”.

2     How to use this Guidance document

• 2.1.    Scope of this Guidance.
• 2.2.    Structure of the Guidance document.
• 2.3.    Study types.
• 2.3.1.    Screening LCA.
• 2.3.2.    Simplified LCA.
• 2.3.3.    Complete LCA.
• 2.3.4.    Summary of the study type definitions.
• 2.4.    How to conduct an LCA study within the field of Energy efficient Buildings.
• 2.4.1.    How to commence and proceed with an LCA study.
• 2.4.2.    LCA study setup: Generic template.
• 2.4.3.    Use of a baseline scenario.
• 2.5.    Compliance with this Guidance.
• 2.6.    LCA studies within research projects of the Energy efficient Building European Initiative (E2B EI).
• 2.7.    An introduction to service life planning.
• 2.8.   Further information and training materials.

Back to EeBGuide Guidance Document Part B: BUILDINGS

Several of the aspects addressed in this guidance define a ‘standard set of parameter values’ for a study, e.g. a default reference study period. This standard set of parameter values is denoted as baseline scenario and provides a basis that allows for comparisons between different studies, e.g. two building LCA studies. The baseline scenario generally contains the definitions and parameter value choices from EN 15804 (products) and EN 15978 (buildings).

Additionally, standard values for a parameter frequently contain options to explore the implications of different choices (e.g. reduced or extended reference study periods). If such deviations are chosen, sensitivity analysis has to be undertaken to compare the new scenario against the baseline scenario in order to explore the influence of the parameter value on the results. Then, results with the use of the default parameter value (baseline scenario) and with modified parameter values (assessed situation) should be compared.

The baseline scenario (i.e. standard set of parameter values) contains the following provisions:

Table 4: Standard set of parameter values for the baseline scenario

2     How to use this Guidance document

• 2.1.    Scope of this Guidance.
• 2.2.    Structure of the Guidance document.
• 2.3.    Study types.
• 2.3.1.    Screening LCA.
• 2.3.2.    Simplified LCA.
• 2.3.3.    Complete LCA.
• 2.3.4.    Summary of the study type definitions.
• 2.4.    How to conduct an LCA study within the field of Energy efficient Buildings.
• 2.4.1.    How to commence and proceed with an LCA study.
• 2.4.2.    LCA study setup: Generic template.
• 2.4.3.    Use of a baseline scenario.
• 2.5.    Compliance with this Guidance.
• 2.6.    LCA studies within research projects of the Energy efficient Building European Initiative (E2B EI).
• 2.7.    An introduction to service life planning.
• 2.8.   Further information and training materials.

Back to EeBGuide Guidance Document Part B: BUILDINGS