Life-cycle assessment is a process or technique to evaluate the environmental impacts associated with a product over its entire life-span. In the case of a building, life-cycle assessment evaluates the impact of all building materials used in a building through all the stages of its life which include extraction of material, manufacture, transportation, use, and final disposal or end of life. Life–cycle assessment can be used to evaluate the overall environmental impact of the whole building or to quantify the impact of a single material in the building.
LEED 2009 awarded points for building material reuse; however, LEED v4 awards points for whole building life-cycle assessment under the “Building Life-Cycle Impact Reduction” credit in the Material and Resources category.
There are two variants under life-cycle assessment:
Cradle-to-grave (open loop assessment): The cradle-to-grave life-cycle assessment approach includes assessment from the resource extraction phase to disposal phase
Cradle-to-cradle (closed loop assessment): The cradle-to-cradle life-cycle assessment approach is where the end-of life disposal phase for a product is a recycling process.
Benefits of LCA
The use of LCA early in the design phase can help evaluate which design options would help to reduce the environmental impact of the building. It can influence design decisions regarding material selection (e.g. type of insulation, cladding material, etc.), structural system choice (e.g. wood frame structure v/s concrete or steel structure) and the quantity of materials required (e.g. number of columns or amount of insulation). LCA can help evaluate the trade-off between material selection, material quantity and energy performance (e.g. type and thickness of insulation v/s energy performance).
Most common environmental impact categories
- Global warming potential: evaluates the greenhouse gas emissions during the life of a building and is a measure of how much heat the greenhouse gas traps in the atmosphere.
- Depletion of stratospheric ozone layer: evaluates the emissions of chemicals over the life of a building (e.g. halocarbons such as CFCs, halons, etc.) that causes depletion of the stratospheric ozone layer.
- Acidification of land and water resources: measures the acidifying effect of materials and emissions during the life of the building.
- Eutrophication: pollution of water resources caused by increased plant and algae growth due to increased availability of one or more growth factors needed for photosynthesis such as sunlight, carbon dioxide and nutrient fertilizers (nitrogen and phosphorus). This depletes the oxygen in water impacting fish and other fauna. This impact category measures the substances or emissions released during the different phases of a building that contributes to eutrophication.
- Formation of tropospheric ozone: evaluates the VOC emissions over the life of a building and measures the potential for the formation of tropospheric ozone or smog.
- Depletion of non-renewable energy resources: quantifies the consumption of non-renewable energy resources by a building over its life-span.
These impact categories are easily quantifiable through the existing LCA tools. Some other less common categories which cannot be accurately evaluated using current LCA tools include human health, ecological, and land-use issues.
LEED v4 offers 3 points for whole-building life-cycle assessment under MR credit – Building Life-Cycle Impact Reduction. The scope for LCA under LEED is the cradle-to-grave assessment. The life-cycle assessment conducted for the project is required to demonstrate at least 10% improvement over a baseline building in at least three of the six common impact categories. One of the three impact categories needs to be global warming potential. LEED also requires that no impact category for the project should increase by more than 5% compared to the baseline reference building.
LEED Baseline Building
The baseline building selected for life-cycle assessment for LEED v4 must be of the same size, serve the same function and have the same service life and orientation as that of the proposed design. The baseline building must meet the ASHRAE 90.1-2010 Appendix G requirements for the same climate zone as that of the proposed design. The LCA must cover the building envelope and structural elements but exclude the electrical, mechanical equipment and plumbing fixtures.
ATHENA Impact Estimator
ATHENA Impact Estimator is a most commonly used simple LCA tool which is populated with background data sets for materials and assemblies that can be used for life-cycle assessment. The tool gathers basic input regarding the project from the users and manages all data and calculations in the background.
The above graph represents life-cycle assessment results for an example project compared to a reference design analyzed using ATHENA. ATHENA has the capabilities to generate the life-cycle assessment results in the format required by LEED v4. The graph indicates that the proposed design demonstrates more than 10% improvement in 5 impact categories recognized by LEED; however has more than 5% increase in the ozone depletion category. This is an indication for the project to evaluate the design to identify materials used in the project that contribute to ozone depletion and make a decision regarding the selection or substitution of the material.