Measures of Sustainability
Overview / Embodied Energy / Operating Energy / Exergy / Durability
Externalities / Ecological Footprint / Eco-Labeling / Life Cycle Assessment

Life Cycle Assessment (LCA)
Life cycle assessment is a composite measure of sustainability which draws upon many of the simpler measures presented previously.

"Life Cycle Assessment is a process to evaluate the environmental burdens associated with a product, process, or activity by identifying and quantifying energy and materials used and wastes released to the environment; to assess the impact of those energy and materials used and releases to the environment; and to identify and evaluate opportunities to affect environmental improvements. The assessment includes the entire life cycle of the product,process or activity, encompassing, extracting and processing raw materials; manufacturing, transportation and distribution; use, re-use, maintenance; recycling, and final disposal".

(Guidelines for Life-Cycle Assessment: A Code of Practice, Society for Environmental Toxicology and Chemistry, SETAC, Brussels, 1993.)

The internationally accepted method for evaluating the environmental effects of buildings and their materials is life cycle assessment (LCA). It is a comparative analysis process that evaluates the direct and indirect environmental burdens associated with a product, process, or activity. Life cycle analysis quantifies energy and material usage and environmental releases at each stage of a product's life cvcle, including:

· resource extraction
· manufacturing
· construction
· service
· post-use disposal

Life cycle analysis is considered the best tool because it examines the full range of impacts over all the phases of a building's useful life instead of focusing on any particular stage. Considering the cumulative environmental impacts over the study period (the assumed service life of the building) allows researchers to make a more complete assessment. Refer to the Related Resources + References page for further information on life cycle assessment.

Typical life cycle assessment parameters include:

Material Usage
the amount of material used expressed in its mass and/or volume.

Embodied Energy
the amount of energy associated with extraction, processing, manufacturing, transportation and assembly of building materials.

CO2 Emissions

the emission of carbon dioxide, which contributes to global warming.

Air Pollution
sulphur dioxide, nitrous oxides, methane, particulate and volatile organic compounds.

Solid Waste Generation
the solid waste generated during manufacturing and construction.

Water Pollution
the quantity of water use associated with a material process, including the effluent deposited into water bodies.

Environmental Costs
externalities associated with buildings.


Additional parameters may be used to reflect particular conditions. For example, some building development may impact reductions in biodiversity. Where nuclear powered electricity generation powers the building, radioactive waste may be a relevant assessment parameter.

The major drawbacks with life cycle assessment methods are the time and cost associated with performing rigorous assessments. In some cases, data for some of the assessment parameters listed above are not readily available. From the perspective of the architect, it is also difficult to justify the development of several design alternatives for the purposes of objective comparison.

There are also difficulties associated with the representation of environmental impacts among alternatives. The use of ecoprofiles, as depicted to the right, can simplify the interpretation of life cycle assessments, however, there may be problems associated with achieving consensus on thresholds of sustainability

When compared to eco-labels, ecoprofiles are far less consumer friendly, but have the advantage of conveniently portraying quantitative data. Irrespective of the means used to represent the outcomes of life cycle assessments, they remain beyond the realm of contemporary architectural practice on a project-by-project basis. Fundamental research into typical buildings with various levels of environmental friendliness, however, could provide useful indicators of the sensitivity of various technical strategies to the overall performance of the building. This would enable the allocation of limited dollars to those investments which are deemed most critical and practically attainable.

Use of an Ecoprofile to Represent Environmental Impacts of Buildings [Adapted from: Life Cycle Assessment Applied to the Comparative Evaluation of Single Family Houses in the French Context by B.L.P. Peuportier, Energy and Buildings Vol. 33, 2001.]
Life Cycle Costing
Another variation of life cycle assessments is life cycle costing which involves financial forecasts of building performance based on construction, operation and maintenance costs. This technique relies on the time value of money and expresses the building life cycle cost as a net present value. In other words, the total cost of building, operating and maintaining the building is expressed as a single sum of money needed today to cover these costs over the study period selected for the life cycle costing exercise. Monetized externalities can be factored into this type of assessment to express the performance of the building in dollar terms. In general, investments in energy saving improvements are found cost effective when the escalation rate of energy costs exceeds the rate of inflation, as is currently the trend.

This technique is suited to formulating regulations, and to institutional projects or situations where the owner will retain the building for a relatively long time, say 20 years or longer. Life cycle costing studies have been used to optimize levels of thermal insulation in building codes, and other investments which go beyond minimum requirements of codes and standards. The National Institute of Standards and Technology (NIST) in the United States has developed and made freely available software which performs these analyses according to American Society of Testing and Materials standard ASTM E 917-93, Practice for Measuring Life-Cycle Costs of Buildings and Building Systems, ASTM Standards on Building Economics, Third Edition, 1994.

The figure below qualitatively indicates the life cycle cost relationship between various qualities of buildings, ranging from the conventional type meeting minimum standards, up to what is currently considered sustainable. Investments in solar (photovoltaic) and wind power generation technologies may eventually result in cumulative life cycle costs falling below the original construction cost, assuming escalating costs for energy over the next century.

Despite the quantitative clarity of life cycle assessments and the ability to monetize many of the parameters which are evaluated, their use is largely limited to research rather than practice. The trend in measures of sustainability is away from the numerical components of life cycle assessments, towards labeling programs for buildings which parallel eco-labeling for products.

The next section on Sustainable Architecture Programs and Evaluation Tools explains how quantitative life cycle assessments are converted into more qualitative and digestible measures of sustainable architecture.

Life Cycle Cost Relationships Between Building Alternatives

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