Each building tells many stories, and one of those stories is its impact on the environment. To understand this story, we can look at the greenhouse gas emissions of all the materials used to erect a building, as well as the energy it took to turn those raw resources into a habitable structure.
Learn how the concept of embodied energy has shaped the face of sustainable design and which materials have the most significant impact on global carbon emissions. We will also look at how architects and construction companies are using the idea of embodied energy to build a greener future, and the new terms used to refine this idea.
What is gray energy?
Embodied energy, also known as embodied carbon, refers to the total amount of carbon expended in the initial creation of buildings. This includes extracting and manufacturing building materials, transporting materials to construction sites, and constructing the buildings themselves.
All materials used in construction, including but not limited to concrete, wood, aluminum, steel, glass and plastic, currently rely on burning fossil fuels during mining, manufacturing, transportation and construction. Once buildings are erected, they “embody” the carbon expenditure of the resources needed to build them.
However, this embodied energy does not literally reside inside the structures – these emissions have already been released into the atmosphere. This is why some sustainability experts prefer the term upfront carbon emissions, which more accurately describes energy expenditures, a term coined by Treehugger’s Lloyd Alter.
Life cycle emissions
Embodied energy is distinct from lifecycle emissions, which include a building’s operational emissions (lighting, heating, and cooling, for example), initial carbon emissions, as well as eventual disposal of building materials.
In previous decades, operational emissions far exceeded the embodied energy of buildings. But as operational efficiency has increased, embodied energy or upfront carbon plays a much larger role in life cycle emissions. In the most efficient buildings, sometimes up to 95% of their lifecycle carbon expenditure occurs during initial construction.
How Embodied Energy is Used in Sustainable Architecture and Design
As architects, construction companies and designers consider the IPCC’s urgent call to cut global carbon emissions by 43% by 2030, some sustainable building experts say it’s much “greener” to preserve the embodied energy of existing buildings.
Construction is one of the fastest growing sources of carbon spending and currently accounts for nearly 40% of energy-related carbon emissions globally, according to the Institution of Structural Engineers in the UK .
Cement production alone accounts for 5-7% of global emissions, with one tonne of cement production releasing 900 kilograms of carbon into the atmosphere. In 2012, the steel industry accounted for 31% of industrial carbon emissions. A 2022 study conducted in China revealed that more than 70% of the embodied energy of all building materials resides in cement, steel and brick.
When a building is demolished to make way for a new one, all of its embodied energy is wasted and a new building with its own initial carbon requirements must be constructed. Investing both money and carbon expenditure to retrofit existing buildings for better operational efficiency causes these new carbon emissions to become part of the building’s embodied energy. In preserving and updating existing buildings, the intrinsic energy of the original construction remains.
For buildings of historical significance, in particular, embodied energy represents a huge existing resource that can be preserved and updated to meet contemporary efficiency standards. Building and architectural professionals depend on research to guide their design choices, but unfortunately, current sustainability rating systems do not reflect fair quantification of historic buildings, according to a 2005 study.
Critics of this reasoning counter that the “sunk cost” – the carbon already spent to create existing buildings – should not dictate future building choices, as those emissions are already in the atmosphere. What should be of most concern, they say, is future carbon expenditures, whether from operational or retrofit emissions.
How is embodied energy measured?
There is no single international standard that clearly defines the embodied energy of any material element, including buildings, making it one of the great challenges facing sustainable designers. This is mainly because construction materials and their subsequent emissions vary greatly, even within the same country.
In general, the embodied energy of a building is calculated as the equivalent of carbon emissions in kilograms per volume of material (kgC02e/m3). The materials themselves are measured in kilograms, and each material’s carbon factor is calculated as an equivalence (the e in the equation above) of the carbon emissions per kilogram of material.
These metrics, again, are separate from operational emissions, which in the United States are often calculated in terms of pounds of carbon per square foot per year.
Why embodied energy is important for sustainability
Experts in sustainable design and architecture can use embodied carbon as a design metric when considering both renovation and new construction. The earlier in the process the design team considers these pressing issues, the more likely the project is to achieve its highest level of sustainability.
This process requires time and dedication, as many changes may need to be made after a given building’s embodied energy assessment. This applies to both commercial and residential structures (and residential buildings use the largest share of energy and natural resources).
For people who pay for energy and water for residential and commercial buildings, operational efficiency often acts as a cost-cutting tool. Heating and cooling costs, for example, decrease in proportion to the better insulation of a building.
But sometimes the more environmentally friendly solution is more expensive. Take aluminum, the second most used metal in the world. Aluminum production accounts for 3.5% of global electricity consumption, the majority of which comes from the combustion of fossil fuels. A 2020 study found that low- or low-carbon electricity costs would increase by 26% in order to meet EU carbon emissions targets. Unlike plastics, which have virtually no recyclability, aluminum is easily recyclable and requires less than 5% of the energy needed to produce new aluminum.
The future of embodied energy and sustainable architecture lies in the use of recycled or reclaimed materials, raw building materials that use fewer natural resources to produce (i.e. less concrete), and a better planning for the long-term use of the land and the buildings we place on it.
Frequently Asked Questions
What is gray energy?
Embodied energy is the total initial carbon emissions expelled during the extraction, manufacturing, transportation and construction of buildings and building materials. This initial energy investment remains for the life of the building.
How is gray energy measured?
Because embodied energy represents the production and construction of buildings, it is measured in carbon equivalent (in kilograms) released per kilogram of building material, written in kgC02e/m3.