Throughout their life cycle, from conception to disassembly, buildings affect natural and cultural ecologies at regional and global scales. Life Cycle Assessment (LCA) methods can measure these material and energy flows inherent to the building. Long-lived buildings reduce the share of embodied resources and environmental impacts borne by each generation that inhabits them: making durability an imperative for sustainability.
Constructing a building on a specific site also creates a globe-spanning web of physical relationships based on the resource extraction, refinement, transportation, and assembly of materials. Even simple building materials may contain many constituent elements and require many steps and processes. This map illustrates one of the many life cycle impacts of a building: its journey through the modern global economy. While not exhaustive in the materials or processes, the complexity of the map reveals economic, social, and resource disparities across the world generated by four built examples. The flows may suggest materials move freely across territorial boundaries, but the traces of economic agreements, and even colonial history remain.
How We Measure—Gross Versus Net
How We Measure—Per Person
Among other environmental consequences, making materials and assembling them contributes to global warming. For simplicity, we sum up those contributions as if they all came from carbon dioxide, use units of carbon dioxide equivalent (CO₂eq) to measure and use carbon as a shorthand for global warming potential. Although the greenhouse gases are emitted into the atmosphere, their environmental impact is embodied, or built into in the material, thus embodied carbon.
To measure the environmental impact of material choices rather than the occupants or operations, this wall of the exhibition tallies each building’s emissions from cradle to gate, including everything from raw resource extraction to a finished but unoccupied building. Unlike the wall behind and to your right, these tallies do not consider building lifespan, or what happens to the materials when the building reaches end of life.
The four buildings in this exhibition are different sizes. To compare them, the total embodied carbon of each is normalized, or divided by units of floor area. The way we measure and compare buildings profoundly shapes our thinking about embodied carbon and its relationship to decisions about building compactness, spatial efficiency, urban form, and density. These graphs illustrate different ways to measure embodied carbon, providing different perspectives on performance.
This composite object compares the sizes of columns made of steel, concrete, timber, and brick that support the same weight.
Curator Michelle Laboy explains the object referred to as the "Wedding Cake", which shows four columns stacked on top of each other. Each column is made of one of the four different materials to illustrate how much of each material it takes to support the same weight load.
Material choices in architecture are measured in and over time as well as space; not only do durable buildings replace fewer components, they divide their environmental impact over a longer time.
These graphs measure the global warming potential from each example building’s construction, repair, maintenance and replacement, as well as demolition and the subsequent reuse or recycling of materials. In addition to the four examples, it includes a data for a typical contemporary building with a short life and frequent replacement. The stacked bars on the left show a baseline, as if the building were demolished as soon as it was constructed. The lines extending to the right illustrate the accumulating environmental impact of each building depending on how long they last.
Like the rest of this exhibition, these data do not include the carbon from the operating energy used for heating, cooling, lighting, and equipment. Unlike the data in “How we Measure Matters” this wall includes the end of a building’s life, so metals may be recycled, while wood releases carbon by decomposing or burning.