April 2011

Volume 20, Number 4

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Embodied Carbon: Measuring How Building Materials Affect Climate

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Carbon Footprint of Nylon Carpet

Carbon.jpg

Source: Interface Global

It’s easy to see how operating buildings emits greenhouse gases. Just as real but harder to see is how buying and installing building materials, products, and appliances causes emissions. Embodied carbon is a measure of the carbon emitted into the atmosphere in order to produce any of these things

Carbon is frequently used as shorthand for either carbon dioxide (CO2) or carbon dioxide equivalents (CO2-e), which includes both CO2 and other gases with significant global warming potential (GWP), meaning that they tend to trap heat in our atmosphere.

Once each greenhouse gas is on the same carbon-equivalent scale, emissions for a specific material can be added up to get its total embodied CO2-e. A lot of a product’s or building’s embodied carbon comes from energy consumption, but not all of it. Blowing agents used in some insulation materials have very high GWP values for example. (Another common measure, embodied energy, captures energy consumption alone.)

The embodied carbon of a product usually includes CO2-e emitted from the extraction of raw materials through the final manufacture of the product, sometimes referred to as “cradle-to-gate.” The embodied carbon of new construction includes all that, plus transport and installation of all of the products and materials that make up the building. Some measures include emissions from construction activity, such as equipment use, transportation of workers to and from the job site, and even land disturbance in construction (which causes loss of carbon stored in healthy soils). As with the more comprehensive life-cycle analysis (LCA), our definition of what is and isn’t included in the calculation has to be consistent to be useful. For building products, work is ongoing in defining these boundaries through product category rules.

An increasing proportion of the total energy use and carbon emissions for high-performance buildings comes from its materials and products. This isn’t only because less energy is used in operation: buildings may be using more materials, and more carbon-intensive materials, to achieve lower energy use. By taking embodied carbon into account, we can ensure we’re designing for net carbon emission reductions.

Another reason to address embodied carbon is that reductions in carbon emissions of materials have an immediate benefit, while the carbon reductions through operations accrue over a long period of time. To minimize severe climate change, the goal is to reduce the total quantity of greenhouse gasses getting into the atmosphere as quickly as possible, so reducing embodied carbon of building materials has an important role.

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March 30, 2011