G-07 (Buildings) / G-08 (Products) Functional equivalent vs. functional unit vs. declared unit

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Aspect G-07 (Buildings) / G-08 (Products) Functional equivalent vs. functional unit vs. declared unit
Description
 ISO 14040, ISO 14044 and EN 15804 define a functional unit; EN 15804 also defines a declared unit. EN 15978 defines a functional equivalent.What are the differences, and when should which term be used?

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 ISO 14040 and 14044, as the basic LCA standards, define the ‘functional unit’ as the quantification of the performance of a product system, and specify that is used as the reference unit for the LCA and any comparative assertion.The term ‘functional equivalent’ is defined in EN 15978 as denoting the technical characteristics and functionalities of the building that is being assessed.The term ‘functional unit’, as defined in EN 15804, refers to the quantification of identified functions or performance characteristics of products. The function/performance characteristics of the product are defined at the building level. The functional unit is used primarily as the reference unit for the product LCA study.The term ‘declared unit’ is specific to product LCAs, as defined in EN 15804. It is used instead of the ‘functional unit’ if the specific function of a product at the building level is not known. EN 15804 states that the declared unit shall be used if an LCA study does not cover the entire life cycle (‘cradle to grave’), but only certain modules (e.g. only ‘cradle to gate’).The terms should be used in line with the definitions of the standards to allow for improved consistency of LCA studies within the construction sector.
Rules from:

EN 15978

 7.2 Functional equivalent

EN 15804

 5.3 Comparability of EPD for building products
6.3.1 Functional unit
6.3.2 Declared unit

ILCD

 Provisions: 6.4 Function, functional unit, and reference flow
• I) SHALL – Identify system or process
• II) MAY – Photos, specifications
• III) SHALL – Identify function(s) and functional unit(s)
• IV) SHALL – Functional unit, details
o IV.a) Function provided (what),
o IV.b) in which quantity (how much),
o IV.c) for what duration (how long),
o IV.d) to what quality (in what way and how well is the function provided (what)• V) MAY – Obligatory and positioning properties
• VI) SHALL – Measurement methods
• VII) SHOULD – Alternatives and complements to the functional unit
o VII.a) Materials and other application unspecific products
o VII.b) Monofunctional processes
o VII.c) Multifunctional processes
• VII) SHOULD – Highly variable function
• VII) SHALL – Comparative studies
Guidance
 The distinction between functional unit, declared unit and functional equivalent is specific to the European construction sector, as they are defined in the CEN standards. LCA practitioners who are not thoroughly familiar with these standards may find it difficult to understand the details of this differentiation.In general life cycle thinking, and for the practical purpose of conducting an LCA, the differences in definition and understanding are not critical to conducting an LCA study. All definitions essentially require the technical performance of the object of assessment to be quantified, and they require a comparative quantification for the case of comparative assertions and meaningful reference units, if the results of an LCA study are intended to be used elsewhere (e.g. the results of a product LCA to be used in a building LCA).For practical application, it is recommended that the terminology of the standards be used. It is essential for the success of an LCA study to define the relevant functions carefully, and to identify the appropriate reference unit, as this is the essential basis for any comparison and/or reuse of LCA data.

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