75% of the global carbon emissions come from the built environment, with 40% being from buildings alone. To effectively reduce overall carbon emissions within the buildings, it is essential to track carbon emissions that result from new construction, major renovations, and even retrofits. All alterations to the built environment have a carbon consequence, whether it’s a positive carbon consequence, like the increase in plantings that sequester carbon, or a negative carbon consequence, like the increase of low albedo asphalt paving. These carbon consequences are measured and tracked so architects and designers know where it is most effective to reduce or offset carbon emissions; this is done through whole-building life cycle assessments.
Whole-building life cycle assessment, often abbreviated as wbLCA, is a method of tracking carbon emissions throughout a building’s life cycle. A building’s life cycle is divided into five stages: Product, Construction, Maintenance and Use, End of Life, and Beyond Life cycle. These stages are divided into modules denoted by a letter and a number (i.e., A3). The Product stage (A1-A3) assesses the carbon emissions associated with raw materials extraction, transportation to a manufacturing facility, and the manufacturing process. Within the Construction stage (A4-A5) the carbon emissions associated with transporting materials to the project site and the construction process are assessed. The Maintenance and Use stage (B1-B7) encompasses the largest portion of a building’s life, including the carbon assessment of any repairs, replacement, refurbishment, and maintenance. Unlike other life-cycle stages, this stage includes modules (B6-B7) that track operational carbon emissions associated with energy and water consumption.
While operational carbon emissions are sometimes excluded from wbLCA since this assessment is mainly used to track embodied carbon emissions, many new greenhouse gas (GHG) accounting standards require the inclusion of these modules within the carbon assessment boundary. The End-of-Life stage (C1-C4) assesses the carbon emissions from building demolition, transportation of waste materials, and the final destination of waste materials, whether it’s a recycling plant or disposal center (landfill or incinerator). Within the Beyond Life Cycle stage (D) any recovery or reuse efforts are captured within the assessment. These will likely be positive carbon consequences since building materials are diverted from disposal.
Architects and designers can do many things to impact each of the described life cycle stages. One way is through product specifications. Specifying products with Environmental Product Declarations, abbreviated as EPD, ensures an accurate carbon analysis. On an EPD, the carbon emissions of the product are evaluated for each life cycle stage, allowing architects and designers to compare the carbon intensities of various products. This ultimately results in smarter choices in materials. The choice of the manufacturer has an impact as well. Specifying products from manufacturers with plants located near the project site should also be prioritized. Manufacturers with a local presence will lower the transportation distance, and lower carbon emissions associated with the transport of products to the site. Selecting manufacturers with take-back programs is another way to lower carbon emissions in the End-of-Life stage since the materials will be recovered and diverted from landfills and incinerators. Another way architects and designers can impact carbon emissions in a building’s life cycle is by designing for flexibility. As mentioned, the Maintenance and Use stage is the longest portion of the building's life cycle. Allowing for multiple uses and the ability to change interior layouts can decrease the frequency of carbon-intensive changes to the building.
The best way for architects and designers to have the most impact on carbon emissions is to utilize the results of whole building life cycle assessments to craft a carbon-reducing design strategy. Not every project has the ability to limit carbon emissions in every single life cycle stage, so isolating where the greatest impact can be made and targeting those select life cycle stages can help reduce overall carbon emissions in the building sector.