Last edited 18 Apr 2022

Life cycle assessment


[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 LCA, 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 (ref. G P Hammond 2007).

The ISO 14040 standard refers to LCA as ‘the collection and assessment of the inputs and outputs of any potential environmental impacts caused by the product system throughout its life cycle’ (ref. British Standard 2006).

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

Approaches that are categorised as level one 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 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 (ref. 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, but also assess social sustainability and health aspects of a building design. 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 LCA 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 LCAs 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 LCA consists of four stages:

The LCA report should be structured in the following form according to EN15978

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 LCA 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 1 sq. m 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, “1 sq. m of roof construction, measured horizontally, to satisfy Building Regulations, in particular to a U value of 0.25 W/m2K. To include any repair, refurbishment or replacement over a 60 year building life” (Anderson, Shiers et al. 2009).

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

Inevitably when completing an LCA of a complex building structure the data can be difficult to access. 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).

There are many tools that undertake Life Cycle Assessment, some of which use the same databases. An EN15978 compliant LCA using the same database should yield broadly similar results as the methodologies under the standard are now clearly defined.

One area of sensitivity is how 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). The approach of EN15978 is to assume todays conditions are identical throughout the buildings life cycle, a good LCA study will recognise this limitation and provide sensitivity analysis

[edit] Related articles on Designing Buildings

[edit] External references


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