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Last edited 28 Mar 2016

Life cycle assessment

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[edit] Introduction

Life Cycle Assessment (LCA) is a method for evaluating the environmental load of processes and products during their life cycle from cradle to grave (Ortiz, Castells et al. 2009). It attempts to identify the environmental effects during all stages of the life of a product and produces a figure (or several figures) that represent the environmental load of a product (Finch 1994). It is a process that is becoming more widely adopted in the context of national and international environmental regulations.

In a full Life Cycle Assessment, the energy and materials used, along with waste and pollutants produced as a consequence of a product or activity are quantified over the whole life cycle (G P Hammond 2007). The ISO 14040 standard refers to Life Cycle Assessment as, ‘the collection and assessment of the inputs and outputs of any potential environmental impacts caused by the product system throughout its life cycle,’ (Bristish Standard 2006).

Life Cycle Assessment tools for use in environmental assessment can be classified in three levels (Haapio and Viitaniemi 2008; Ortiz, Castells et al. 2009):

  • Level 1: Product comparison tools, such as Gabi (Germany), SimaPro (Netherlands), TEAM (France) and Umberto (Germany).
  • Level 2: Whole-building design or decision support tools such as Envest (UK), ATHENA (Canada) and Ecoquantum (Netherlands).
  • Level 3: Whole-building assessment frameworks or systems such as BREEAM (UK), LEED (USA) and SEDA (Aus).

Approaches that are categorised as level one are referred to a bottom-up approaches, as they focus on individual materials and components. These components are then summed together to form a Life Cycle Assessment for the entire building.

Level 2 tools are considered top-down in their approach as they consider the entire building as the starting point. For example their starting point may be the shape of the building and then gradually work down through the construction to the choice of materials in the frame, infill walls and so on (Erlandsson and Borg 2003).

Level 3 approaches tend to be comparative scoring systems that can be applied across the building sector. They consider the whole life of the product in some sense, however, it has been argued that they are essentially a scoring system to benchmark different buildings, based on predefined and generic environmental performance. Erlandsson and Borg (2003) suggest this is inadequate as the environmental performance of a building is dependent on its context (such as geographical location, requirements for foundations, logistic context and so on). They argue that each building should be competing with itself, in order to make the best choices based on its unique context. Others believe that level 3 building assessment frameworks do have their place in the construction sector, as they guide whole-life and environmentally focused design through competition between clients. They are also useful in informing the design process.

The approach taken to Life Cycle Assessment will be driven by the decisions that need to made. Obviously the more detail that is required, the harder and more onerous the task, but the more project specific the answer will be. In reality the approach is likely to be a hybrid, where more information is used where it is easier or more important and more generic information elsewhere.

[edit] Formalities of analysis

ISO 14040, 14041 and 14044 provide guidance about how Life Cycle Assessments should be carried out. Principally the expectation is that the approach to the problem is consistent and transparent in terms of how data is gathered, analysed and presented.

A full Life Cycle Assessment consists of four stages:

  • Scoping (ISO 14040 & ISO 14041). To determine the aims and objectives of the study.
  • Inventory Analysis (ISO 14041). The creation of a complete list of inputs to, and outputs from the system.
  • Impact Assessment (ISO 14042). The evaluation of those inputs and outputs on the environment.
  • Improvement Analysis (ISO 14043). The evaluation of proposed modifications to the system to reduce the overall environmental impact.

The Life Cycle Assessment report should be structured in the following form:

  • Goal & scope definition.
  • Inventory analysis.
  • Impact assessment.
  • Interpretation of results.

These standards cover the principles of analysis for all environmental impacts not just carbon dioxide.

PAS 2050 is specific to climate change, and so only considers carbon dioxide equivalent. It is also more prescriptive about how the analysis is done; for instance it looks at the impact of the product over a 100 year lifetime, and it defines which emissions to include and exclude. Because PAS 2050 only looks at emissions over a 100 year horizon and heavily discounts future emissions it may be more suited to simple products such as furniture and ironmongery than to buildings.

When conducting a Life Cycle Assessment it is essential that the boundaries of the system to be analysed are clearly defined. For example should it include only the processes that occur within the building, or the processes that are associated with the entire building plot? And what about the energy and material used to travel to and from the building?

A functional unit is a unit across which two materials or products perform the same function and can be compared. For example comparing steel and concrete structures on a per tonne basis would be meaningless as steel may have a large impact per tonne but much less may be required to perform the same function, for example providing structure for 1m2 of floor space.

For some elements, such as an external wall or roof, the functional unit also takes into account the thermal resistance of the construction to ensure that all specifications are compared on a like for like basis (as in the Green Guide to Specification). The functional unit for roofs as defined in the Green Guide to Specification is, “1m2 of roof construction, measured horizontally, to satisfy Building Regulations, in particular to a U value of 0.25W/m2K. To include any repair, refurbishment or replacement over a 60 year building life” (Anderson, Shiers et al. 2009).

Software packages are available for undertaking Life Cycle Assessment of products. However software simulation packages for buildings in their environments are still relatively primitive (Halliday 2008).

Life Cycle Assessment is widely used in the manufacturing industry and has greatest value when products are mass produced. Regulations have led companies to undertake whole life assessments of their products to not only identify their environmental impact, but also to identify possible cost savings through the identification of waste streams and the use of restricted materials and processes.

[edit] Limitations of life cycle assessment

One of the significant limitations to Life Cycle Assessment is that it is time consuming and data intensive (G P Hammond 2007). “The extent of information necessary to carry out a life cycle assessment is immense” (Finch 1994). Additionally much of the data required is difficult to access and not in the public domain. This can lead to data gaps in the assessment. These are handled in different ways by the different tools. Some use best estimates to deal with data gaps, some leave data gaps blank, whilst others collect more data to fill known data gaps (Erlandsson and Borg 2003).

Finch (1994) argues that a fundamental flaw in Life Cycle Assessment is the unrelatedness of the information to the clientsdecision making process, as no information in the process is reduced to a form in which the client can rationalise the environment-cost trade off. This is significant as ultimately Life Cycle Assessment is a tool for aiding decision making, and if it is not relevant, its purpose is questionable.

Finch also suggests that Life Cycle Assessment focuses attention on product selection at the design stage (Level 1), whilst environmental assessment must recognise the holistic nature of design. It is the combined performance of systems and assemblies, not the isolated history of specific components which produce a good environmental solution.

This returns us to choosing an appropriate system boundary. Unfortunately for the construction industry, the systems boundary would ideally be on a building scale or larger, however, the complexity of Life Cycle Assessment at this scale becomes substantially more time consuming and resources intensive. The greatest limitation to the full Life Cycle Assessment of a building is that each building is bespoke and unique, whereas Life Cycle Assessment is of the greatest benefit for large-volume, short-life products, such as consumer goods, where cost savings and process innovations can be identified through the life cycle.

There are many tools that undertake Life Cycle Assessment, some of which use the same databases. However, as they give different results because of the way they handle information there can be some scepticism about the results. One reason for this is the use of different techniques to interpret ‘time dependence’. Time dependence refers to the impacts on the system being analysed due to changes in the external environment within which the system sits. For example in the case of buildings, which can realistically have a design life of 100 years, there is a significant difference in the average environmental load per year. This can be attributed to factors such as the development of renewable energy sources within the energy sector (Erlandsson and Borg 2003). Many Life Cycle Assessment tools are unable to take account of changes that are certain to happen within the long life of a building. To do so would involve making assumptions about the future, or providing the user with the ability to make these assumptions in their assessment (Erlandsson and Borg 2003). This is an area in which further development is essential.


This article was created by --Buro Happold.

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[edit] Related articles on Designing Buildings Wiki

[edit] External references

  • Anderson, J., D. Shiers, et al. (2009). The Green Guide to Specification, BRE.
  • Bristish Standard (2006). BS EN ISO 14040:2006 - Environmental management - life cycle assessment - principles and framework.
  • Erlandsson, M. and M. Borg (2003). Generic LCA-methodology applicable for buildings, constructions and operation services--today practice and development needs. 38: 919-938.
  • Finch, E. F. (1994). "The uncertain role of life cycle costing in the renewable energy debate." Renewable Energy 5(5-8): 1436-1443.
  • G P Hammond, A. B. W. (2007). "Interdisciplinary perspective on environmental appraisal and valuation techniques." Proceedings of the Institute of Civil Engineers.
  • Haapio, A. and P. Viitaniemi (2008). "A critical review of building environmental assessment tools." Environmental Impact Assessment Review 28(7): 469-482.
  • Halliday, S. (2008). Sustainable Construction. Slovenia, Butterworth-Heinemann.
  • Ortiz, O., F. Castells, et al. (2009). "Sustainability in the construction industry: A review of recent developments based on LCA." Construction and Building Materials 23(1): 28-39.
  • Peris Mora, E. (2007). "Life cycle, sustainability and the transcendent quality of building materials." Building and Environment 42(3): 1329-1334.

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