To initiate change of any kind, one must first be aware of the problem at hand. In the construction industry –which is responsible for 39% of global greenhouse gas emissions and countless other environmental impacts– mastering and understanding the numbers related to its processes is extremely important. But assessing the impact of a product or a material is much more complex than one might think. It includes the exhaustive collection of data about its inputs (for example, the raw materials, energy, and water used) and outputs (such as emissions and waste) associated with each stage of the life cycle. This allows for the quantification of the embodied carbon and other environmental impacts, the identification of where performance can be improved, and provides real numbers for a comprehensive and unified comparison between materials and products.
The Whole Building Life Cycle Assessment (wbLCA) method studies the totality of products present in a building, providing valuable information for decision-making related to the design, construction, operation, maintenance, and eventual demolition or reuse of a building. In other words, it refers to the totality of the LCA (Life Cycle Assessment) for all of the building's components. Recently, the National Research Council of Canada, in collaboration with the Athena Sustainable Materials Institute, released the national guidelines for wbLCA, which reflect what is practiced in North America. The aim is to harmonize the practice and to aid interpretation and compliance with relevant standards, with the guidelines being updated periodically as it evolves, enabling the calculation of reliable baselines or benchmarks, supporting LCA-based compliance schemes and assisting in the development and use of wbLCA software.
While the national guidelines are intended for a specific audience that is already familiar with the method –with guidance on reference units, selection of environmental data, and ways of presenting studies– this article will focus on a general overview of the method, based on a playbook developed by Vancouver-based ZEBx (Zero Emissions Building Exchange).
LCA scientifically quantifies the environmental impacts of resource consumption, emissions and waste over the lifespan of a building, and is a globally accepted method for understanding the environmental footprint of products, processes and buildings. Governments and building owners are increasingly moving toward this method as a way to assess climate change and other environmental impacts of buildings. This document –Demonstrating the Benefits of Whole-Building Life Cycle Assessment– for example, presents nine studies showing the power of wbLCA in commercial, multi-family residence and community hybrid wood buildings in British Columbia, briefly illustrating the different uses of wbLCA. Through it, one can see the considerable reduction of CO2 emissions when adopting low embodied carbon materials, such as wood, in place of traditional building materials. Here are the main steps to develop a wbLCA analysis in a project:
Understanding the Challenge: First Steps
There are a few steps that must be considered in order to develop a comprehensive study. First, it is important to define the objective and scope, such as which building components will be analyzed and the impact categories. According to ISO 14040, the objective of an LCA should indicate the intended application, the reason for conducting the study, the target audience, and whether the results will be public. These decisions will directly impact the parameters that will be assessed in more depth. The analysis is usually applied to advise on building design (comparing solutions, materials, or matching certain certifications), or for policy development (compiling data for benchmarks or informing research).
Although there is no universal definition, generally, a wbLCA analyzes the building structure, elements of the envelopes and interiors, excluding mechanical, electrical and plumbing (MEP) systems and other services, equipment and furniture, as well as other site activities.
The study period (in North America this ranges from 50 to 100 years for the useful life of buildings) and the life cycles included in the LCA also need to be defined. The chart below outlines the assessment system boundaries that are adopted, according to EN 15978, to standardize analyses:
Compiling and quantifying the data
The second stage involves the development of the LCI, or Life Cycle Inventory, which is the compilation and quantification of the inputs and outputs of each phase of the useful life. To do this, it is important to delve into the data sources that the project has available, such as models, technical drawings, documents and others. From these, information about the building's assemblies and material quantities can be collected and calculated. Data sources can be classified by their level of accuracy as primary, project-specific, product-specific and secondary, and the accuracy of the LCA depends on the accuracy and completeness of the data source. Certain construction LCA tools are only compatible with certain types of data sources and BIM models may have much of the material quantities needed to conduct the studies.
The definition of the tool which will be used must be done carefully, since each option uses its own database of environmental impact information, and this will influence the accuracy and applicability of the results.
Choosing the right tool and obtaining the first results
Afterwards comes the Life Cycle Impact Assessment (LCIA) stage, where the chosen LCA tool is used to assess the potential environmental impacts quantified in the LCI. Simplified whole-building LCA tools provide cradle-to-grave LCA results for many generic building assemblies without requiring users to have LCA expertise. Athena Impact Estimator for Buildings, One Click LCA and TallyLCA are the most widely used whole building LCA tools in North America, for example.
The primary input into all LCA tools is a bill of materials (BoM) for the building, which must be analyzed on a component basis to determine the environmental impact of each material component and then summed up according to its assemblies and processes (e.g., what it takes to make a concrete foundation or a steel beam). For materials and products without an exact match, the professional must determine an acceptable substitution. This usually involves finding the closest similar product or material.
It is always important to perform a preliminary review of the results, checking for discrepancies in quantities or material errors in calculations. If the results of the LCA are unexpected or appear incorrect, the practitioner should review these steps and recalculate it.
Interpreting and publishing the studies
Finally, the last steps refer to the interpretation and evaluation of the results, as well as reporting them in a clear and concise manner, including the methods used, the data collected, the results and what could be interpreted. At this point, the designer can have access to the impact percentages per material used, per life cycle or per assembly, obtaining a valuable overview for decision-making.
That said, the wbLCA method provides valuable information for decision-making related to design, construction, operation, maintenance and demolition. It can be an important tool for more conscious gestures and better decisions. For more information, visit the National Guidelines for Whole-building Life Cycle Assessment.
