Emissions and Building Construction
As extreme climate events become more frequent, concern over climate change has grown, and designing buildings to lessen environmental impacts has taken on greater importance. Understanding carbon impacts, environmental implications and associated concepts is crucial to today’s design process. But some terms are more easily understood than others. Here’s a brief explanation of language often used in conversations about carbon and the built environment.
Carbon and Building Materials: Biogenic, Embodied, Operational
Carbon accounting is the process of calculating overall carbon emissions associated with the chosen building materials. It estimates how much carbon is sequestered into materials versus how much carbon is emitted during material extraction and manufacture, construction and eventual demolition and disposal, as well as emissions during habitation of the building.
Biogenic carbon refers to the natural processes where carbon is sequestered into a building material itself, such as the carbon sequestered into wood during tree growth. Biogenic carbon is released when the material decays or is destroyed. Some materials contain no biogenic carbon; others, like wood, contain considerable amounts.
Embodied carbon is often confused with biogenic carbon, but that is a misconception. It does not refer to carbon sequestration. Instead, it refers to emissions related to construction and building materials. These embodied emissions encompass all greenhouse gas emissions that arise from the extraction, manufacture, transport, installation, maintenance and disposal of building materials. Emissions from construction activities, like repairs and remodels, are also included in this category, as are emissions from building demolition and disposal.
Operational carbon is a separate category from materials; it refers to carbon emissions during typical habitation and operation of a building, like heating, cooling and powering the building and its various systems. It does not include any repair or remodel activities. These fall within the category of embodied emissions of building materials.
What about Carbon Neutrality and Net Zero… or is it Zero Net?
Carbon neutral describes a project or operation that balances the amount of carbon emissions it generates with an equal amount of carbon sequestration. Net zero, which is sometimes used interchangeably with carbon neutral, may refer to either embodied emissions or operational emissions, depending on context.
To attain carbon neutrality, carbon is quantified in tons of emission versus tons of sequestration. If these are equally balanced, the project is carbon neutral—or perhaps even carbon negative, if tons of sequestration are greater than tons of emission. Carbon neutrality can be accomplished a number of ways, but often involves planting more trees, investing in reforestation projects and other forms of carbon offsetting. Carbon offset is carbon absorption specifically intended to compensate for carbon emissions in the context of carbon neutrality. Offsets are often purchased as carbon credits (on a one credit per 1 ton sequestered basis) from entities specializing in carbon offsetting.
Net zero, on the other hand, can mean balancing an amount of emissions with the same amount of sequestration, especially when referring to “Net Zero 2050” and other climate goals. But net zero is sometimes interchanged with zero net energy, a term that refers to buildings that have no net power use during operations. Zero net energy buildings often have components that generate power and store it and/or push it back on the grid, compensating for the energy used during operation. For this reason, net zero can be a somewhat confusing term.
Find more, including a glossary of commonly used terms, at www.apawood.org/a-carbon-explainer.