The July column looked at Environmental Product Declarations (EPDs) as a primary resource for comparing the embodied carbon and other environmental impacts of individual materials, working toward reducing embodied carbon in buildings. This month, we will expand on that topic and review whole building life cycle assessment (LCA), a means to quantify and reduce embodied carbon and other impacts of entire structures. Because intuition is often counterintuitive, this analysis is critical to understanding the many impacts of complex systems like buildings. Even simple life cycle comparisons can be challenging without analysis. The Danish EPA did an LCA comparing impacts of single-use plastic bags to reusable options. A polypropylene bag needs to be reused only 37 times to best a plastic bag, but an organic cotton bag requires 20,000 uses to have a lower impact. Let’s explore how LCA can inform complex building design decisions.
Embodied Carbon and Other Project Vitals
What is Whole Building LCA?
Whole building LCA is an inventory of the environmental impacts associated with all the major materials used to construct a building. For each step in the life cycle, the LCA quantifies the parameters related to atmospheric and ecological impacts. The LCA consolidates the Individual environmental impacts of each material in the building, providing an accounting for the whole system.
LCA starts with establishing the boundary for the assessment. It accounts for the cradle-to-grave impacts of all primary structural and enclosure materials, starting with extraction, harvest or recovery of raw materials (but not going farther upstream for recycled/reused materials), and extending through the expected service life of the building, including maintenance and replacement of building components (e.g., roofing). Interior partitions, finishes, furniture, and mechanical, electrical and plumbing systems are not typically part of an LCA scope, but in some cases, it would be informative to include them. Excavation and other site work are also excluded. Whole building LCA establishes a baseline building (conventional, code-complaint structure and shell) that is used as a point of comparison for proposed design alternatives (e.g., structural systems of cladding).
LCA is not related to energy modeling or Life Cycle Cost Analysis (LCCA). Energy modeling provides comparative analysis of the energy use and carbon emissions related to building operation, while LCA looks comprehensively at environmental impacts of the materials used in construction and maintenance. LCCA is sometimes confused with LCA due to the similar acronym, but is very different. LCCA establishes the net-present-value of alternative systems or components, and is most commonly used to quantify the present value of first cost, utility costs and maintenance costs for alternative energy efficiency measures (e.g., HVAC system options).
What Are the Parameters in LCA and How Can We Interpret Them?
LCA typically looks at the following impact indicators:
- Global warming potential (release of greenhouse gasses)
- Ozone depletion potential (stratospheric ozone)
- Acidification potential (acid rain on land and water)
- Smog formation potential (tropospheric ozone)
- Eutrophication potential (algae formation and oxygen depletion in fresh water due to nitrogen and phosphate)
- Non-renewable energy resource depletion (from extraction, manufacturing and transportation)
An LCA may show that some impact indicators for a proposed design are lower, while others have increased compared to the baseline. While it is difficult to weigh the relative importance of each indicator, generally the preferred solution will have most of the indicators improving significantly, and few, if any, increasing in impact, with global warming potential being the most critical to see reduced. Generally, buildings with less material mass will have a lower impact, so minimizing the use of new materials will improve indicators, but sometimes alternatives have interactive results that are counterintuitive. The LCA provides quantified feedback to project teams, informing changes to the design to optimize performance and maximize impact reduction.
Tally Life Cycle Assessment Report
What Tools are Used to Produce an LCA?
LCA tools typically have calculation factors specific to the country where they will be used. The most common LCA tools in the U.S. are:
- Tally – A Revit application developed by Kieran Timberlake Architects, that provides real-time whole building LCA based on a bill of materials generated and updated from the project’s BIM model.
- GaBi – A powerful LCA tool developed by thinkstep, used for conducting LCA for individual products or whole systems, including buildings.
- One Click LCA – Allows users to import building design data from Revit, IES and other modeling tools, and includes an extensive database of materials using both generic and product specific LCAs and EPDs.
LCA and LEED
LEED v4 combined and modified the old Building Reuse and Material Reuse credits into one new credit with four compliance options. The new credit, Building Life-Cycle Impact Reduction, includes options that reward historic and abandon building renovation, building and material reuse, and a forth option based on whole building LCA. This option uses a baseline building enclosure defined by the performance requirements of ASHRAE 90.1-2010, Appendix G, and it sets a minimum building service life of 60 years. The credit is achieved (3 points) if at least three impact indicators (including global warming potential) improve by at least 10 percent, and no indicators increase by more than 5 percent. The LEED v4.1 pilot proposes three compliance paths for this option, including a one-point path for doing an LCA regardless of results, and an advanced four-point path achieved by selecting the design option with the lowest embodied carbon.
AIA Resolution 19-11 calls on architects to take urgent and sustained action to decarbonize buildings. Beyond the traditional focus on cutting operational carbon emissions, reducing embodied carbon is the next frontier. Due to the “time-value-of carbon,” emissions reductions today in embodied carbon are more critical in averting the climate crisis than future operational carbon reductions. Whole building LCA is an import decision making tool to guide building professionals toward positive climate outcomes.
Alan Scott, FAIA, LEED Fellow, LEED AP BD+C, O+M, WELL AP, CEM, is an architect with over 30 years of experience in sustainable building design. He is a Senior Associate with WSP in Portland, Ore. Mohammad Hossein Abbasi, Assoc. AIA, CPHC, LEED AP BD+C is a building performance analyst with WSP in Chicago, helping clients make a better decision on the energy use, health and environmental impact of their buildings. To learn more, visit http://www.wsp.com/en-US/services/built-ecology and follow Alan on Twitter @alanscott_faia.