Life cycle assessment is the compilation and evaluation of inputs, outputs and potential environmental impacts of a product system throughout its life cycle (ISO 14040).

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Learn More About How LCA Works

LCA is the performance approach to sustainable product or building design. It is the logical evolution from today’s reliance on prescriptive methods, whereby materials are deemed to have environmental benefits based on their attributes. For example, recycled content, rapid renewability, and local procurement are all assumed to be environmentally superior characteristics without any supporting data.

LCA measures actual performance, removing the assumptions. It is widely accepted in the international environmental research community as an appropriate method for scientific quantification of an environmental footprint.

What is Being Measured
In LCA, information is gathered at every phase of a product’s life, and viewed through the lens of defined environmental impact measures such as global warming potential, primary energy consumption, air and water pollution, and use of natural resources. Typically, LCA reports on these environmental effects due to a product, building or service:

  • Fossil fuel depletion
  • Other non-renewable resource use
  • Water use
  • Global warming potential
  • Stratospheric ozone depletion
  • Ground level ozone (smog) creation
  • Neutrification/eutrophication of water bodies
  • Acidification and acid deposition (dry and wet)
  • Toxic releases to air, water and land

In LCA terminology, the effects associated with making, transporting, using and disposing of products are referred to as ‘embodied effects’, where the word “embodied” refers to attribution or allocation in an accounting sense as opposed to true physical embodiment. All of the extractions from and releases to nature are embodied effects, and there are also embodied effects associated with the production and transportation of energy itself (known as pre-combustion effects). Note that all phases, but the “use” phase in particular, include environmental accounting of associated activities and their products such as periodic cleaning and repainting. For example, a life cycle assessment for a deck needs to include the energy, water use and detergents involved with cleaning, the various impacts associated with coating products like stain, and the possible replacement of some boards over the life of the deck.

LCA in the Athena Software Tools
The Athena Impact Estimator for Buildings and Pavement LCA are tools with detailed life cycle assessment in the background that provide access to LCA results on construction products and report results for a building or paving project. Impacts are reported as a whole or broken down by life cycle stages:

  1. Resource extraction
  2. Product manufacturing
  3. Construction of the building
  4. Building Occupancy and maintenance
  5. Building demolition/deconstruction/materials end-of-life disposition (disposal or transfer for recycling or reuse)

See the diagram below and detailed description of the life phases.

1. Resource Extraction
The life cycle of most building products starts with the extraction of raw resources like timber, iron ore, coal, limestone, aggregates and gypsum. The development of life cycle inventory data starts here, by tracking energy use and emissions to air, water and land per unit of resource extracted. In addition to the actual harvesting, mining or quarrying of a resource, data from the extraction phase includes activities such as reforestation and beneficiation (a mining technique that involves separating ore into valuable product and waste) and remediation. It also includes the transportation of raw resources to the mill or plant, which defines the boundary between extraction and manufacturing. It is important to understand that LCA does not attempt to address all land-impact measures, many of which are tracked in other environmental metrics or regulatory programs. For example, effects on biodiversity, water quality, and soil stability are difficult to measure, may not have benchmarks or standards to provide a process for measurement, and are entirely site-specific at a small scale. Some of the broad resource issues of concern to many people are not included in LCA.

2. Manufacturing
Manufacturing is the stage that typically accounts for the largest proportion of embodied energy and emissions associated with the life cycle of a building product. In Athena inventory studies, this stage starts with the delivery of raw resources and other materials to the mill or plant gate and ends with the finished product ready for shipment. The Impact Estimator software combines resource extraction and manufacturing into a single activity stage for results reporting purposes. The Athena Institute follows the international Organization for Standardization (ISO) guidelines for product LCAs addressing secondary components and assemblies, data sources and verification, system boundaries, the level of detail expected in inventory studies and a variety of other standard conventions and assumptions, to ensure that all building materials are treated impartially, in a comparable fashion. Athena product LCAs are performed in conjunction with experts in the relevant industries.

3. On-site Construction
The on-site construction stage is like an additional manufacturing step where individual products, components and sub-assemblies come together in the manufacture of the building. In the Athena tools, this stage starts with the transportation of individual products and sub-assemblies from manufacturing facilities to distributors in various Canadian and US regions. Average or typical transportation distances to building sites within each city are applied. This is an important life cycle stage that is often overlooked in life cycle assessments for products alone. In addition to building product transportation, waste generation, and the energy use of machines like cranes and mixers, the on-site construction activity stage includes such items as the transportation of equipment to and from the site, concrete form-work, and temporary heating and ventilation.

4. Occupancy/Maintenance
The occupancy stage takes into account functions like heating, cooling, lighting and water use, as well as the introduction of new products such as paints, stains, floor coverings and other interior finishes. It also considers that a building may be remodeled or reconfigured several times over its life, which introduces new products or systems. In the course of maintenance, some parts of a building will be altered or replaced, but other parts may not be seen or touched until the building is demolished or deconstructed. The Athena Institute has completed studies on the maintenance and replacement of building components for various North American regions. These data form the basis for the Impact Estimator occupancy stage results, whereby the expected life of a component such as roofing or windows is considered across the expected life of the structure so that appropriate product replacements are included. Athena has also developed an operating energy conversion calculator module which allows software users to enter their building’s annual operating energy by fuel type (as calculated using other tools such as energy simulation software); the Impact Estimator will include the pre-combustion and direct combustion emissions associated with the use of those fuels.

5. End of life
Demolition/deconstruction marks the end of a building’s life cycle, although it is not the end for individual component materials or products which face a subsequent recycling/reuse/disposal stage. The Athena Institute has developed LCA data for this life phase. In the Impact Estimator, the original building is charged with all demolition and transportation effects for the materials going to landfill. Recycling, reuse or disposal is the final stage in the life cycle of the individual components or products comprising a building. This part of LCA has a great deal of uncertainty; it involves trying to predict activities that are a long way in the future. The conservative approach is to assume demolition and disposal practices will always remain as they are today, because there is too much uncertainty involved in predicting future waste management practices. The Athena databases take account of recycled materials coming in as raw material for the manufacturing stage for various products (e.g., fly ash in concrete and metal scrap for metal products). The Impact Estimator accounts for the environmental burden of demolishing the building and transporting materials to landfill. The software calculates and presents end-of-life effects in two ways. First, it presents results on the producer pay principle and does not give credit to a building for future reuse of recovered demolition waste or recycled materials because that environmental impact is properly assigned to the next use of the material, not the current use. The second result method includes material recovery, recycling and carbon sequestration scenario effects beyond the building’s life (what is commonly referred to as the “avoided burden” methodology. Both reporting methods are in line with the latest European standards (EN15804 and 15978) and are illustrated in the figure below.

EN 15804 and 15978 System Boundaries

LCA Limitations
Life cycle assessment addresses only some of the characteristics that may fall under a heading of environmental or sustainability concerns. Critics of LCA are often unfairly expecting LCA to reach beyond its intended scope. LCA is a methodological tool that complements other methods of assessing “environmental” impact for a well-rounded picture. For example, LCA does not typically address ultimate human health effects—there are many other metrics and regulations in place for those concerns. A common example is the measurement of indoor air quality and its impact on human health.

Similarly, today’s mainstream LCA impact indicators do not directly address the ultimate effects on ecosystem stability or toxicity. Like human health effects, these have a high degree of difficulty and uncertainty in assessment. This is an area of on-going research in the LCA world. In both these cases, LCA typically stops at “mid-point” indicators rather than “end-point” indicators until the science of end-points becomes more resolved. A mid-point indicator, for example, is the potential for acidification of water bodies. An end-point indicator is a reduction in fish population.

LCA is also sometimes criticized for limited ability to account for land use impacts. These impacts are typically addressed more comprehensively by other metrics such as sustainable forest management programs. LCA does not replace those metrics. One of the difficulties in assessing the environmental effects of resource extraction is that so many of the environmental effects that concern people—for example, biodiversity, water quality and soil stability—are not easily distilled and measured and therefore are often minimally addressed in life cycle inventory studies. In addition, these types of impacts are highly localized and therefore difficult to account for in the mixing of commodity sources within the distribution processes that happen very far upstream in a product’s supply chain. North America lacks LCA protocols for land use impacts; in other words, what to measure and how to measure are not standardized nor even resolved.

Life cycle assessment by definition has some uncertainty as with any calculation that involves assumptions about future conditions. In that sense, it is fundamentally no different than energy simulation. Other variables that affect confidence in or comparability of LCA results include quality of the underlying LCI data, attribution methods and selection of impact indicator frameworks. LCA has matured as a science from earlier days when two different LCA studies on the same products might come up with completely different results. LCA is now an increasingly standardized practice with third-party review and centralized data sources such as the USLCI database, which are helping to minimize disparities.

LCA is a rigorous science, but its precision should not be overstated. By simply introducing the notion of (roughly) calculating the environmental footprint of a building under design, LCA is already a huge leap forward in the evolution from prescriptive to performance-based green design. To expect that LCA will deliver results with a high degree of precision given all the variables involved is asking too much. Consider this limitation in the same light as energy simulations; rather than expect the tool to deliver an absolute performance prediction, LCA is best applied for relative comparisons, to help in choosing one path over another.