Understanding the Carbon Footprint of Building Materials is a key challenge for decarbonizing construction. Embodied emissions, which account for 11 percent of global greenhouse gas emissions, come from the extraction, manufacture, transportation and construction of building materials like concrete, steel, flat glass and insulation.
Reducing embodied carbon emissions requires changing how a project is built. Zoning laws, environmental product declarations (EPDs) and building codes are three policy levers that can help.
Concrete
The second-most widely used material in the world after water, concrete is an indispensable part of our modern world. It supports buildings, footpaths and roads, and it can even be moulded into architectural masterpieces. But concrete comes with a heavy environmental cost. Its main ingredient, cement, which binds aggregates like sand and gravel together, accounts for 8% of global carbon emissions – more than double those from shipping and flying combined.
Fortunately, there are steps being taken to make concrete greener. Some manufacturers are substituting portland cement with waste byproducts such as slag and fly ash, which reduce the concrete’s embodied carbon content by up to 30% or 60%, depending on the manufacturer. However, there aren’t enough of these byproducts to meet the concrete industry’s demand, so research is being undertaken to produce alternative sources.
The embodied carbon of concrete can also be reduced by designing structures to last longer, which requires less maintenance and less energy consumption. Other solutions include using lower carbon materials such as timber, or constructing hybrid structures that combine concrete with other low-carbon materials such as steel. The concrete embodied carbon calculator on this website allows users to enter the specific details of a concrete mix (in terms of its constituents per m3) and calculate its embodied carbon. This can then be exported as a pdf report.
Steel
As the most common structural material in North America, steel is also one of the biggest sources of embodied carbon in a building. Like concrete, it’s a heavy material that requires large amounts of fossil fuel energy to mine, manufacture and transport. The direct carbon emissions from producing steel can be quite high, with some sources putting it at more than three CO2 tons per ton.
Structural systems typically comprise up to 80% of a building’s embodied carbon, so one of the best ways to reduce this footprint is by using less steel in a structure. Composite design, the use of diagonal braces instead of moment frames, and specifying the more efficient shear walls can help reduce the amount of steel required to achieve a project’s structural requirements.
Increasingly, building professionals are looking to lower a building’s overall embodied carbon footprint. Whole-building life cycle analysis (WBLCA) is a good place to start for this, but there are many other resources that can be used to identify carbon “hotspots” and help reduce the building’s footprint.
A number of free online resources are available to assist with this effort. The Bath Inventory of Carbon and Energy (ICE) database is a long-standing and well-respected source, although its data are specific to the U.K. More recent tools include the Quartz database, a website that provides basic environmental-impact and health-related information for 102 common construction materials, and thinkstep’s Embodied Carbon Calculator, which is free to use and offers data for materials in North American.
Glass
Glass is all around us – from the eyeglasses on your face to your bottles and windows. But how much do we know about this versatile – and sometimes misunderstood – material?
For starters, it can be produced in a variety of ways depending on the final product and its end-application. It also has a surprisingly complicated atomic structure, which scientists are learning how to manipulate in new and exciting ways that could lead to big advancements in technology in the future.
The most commonly used type of glass is soda-lime glass, which is typically made from silica sand, soda ash, limestone or dolomite and glass cullets (recycled glass). Additives such as iron oxide can give the glass different colors. To make it, the ingredients are heated to a high temperature until they melt into a molten state. Then the mixture is stirred continuously to remove any remaining impurities, such as metals or abrasive particles. It’s then cooled to a solid state.
This process is very energy intensive, which contributes to a building’s embodied carbon footprint. For this reason, it’s important to consider a building’s whole-life carbon footprint and incorporate the results into any design decisions. One way to do this is by using the Inventory of Carbon and Energy database from Bath University – which you can access for free on this page.
Insulation
Insulation reduces operational energy and carbon emissions in the built environment by limiting energy flow through the envelope. However, the manufacturing of insulation can also emit significant embodied carbon. Through life cycle assessment, the carbon payback between embodied carbon investment and operational savings can be understood.
While the building industry has, to a large extent, been able to reduce the impact of buildings’ operational emissions by switching to renewable energy, the embodied carbon from construction materials still remains high. With embodied carbon representing 11 percent of worldwide GHG emissions, this is a critical aspect of greenbuilding that needs immediate attention.
Embodied carbon consists of the greenhouse gases (GHGs) emitted by the production of concrete, steel and other building materials. This includes the extraction of natural resources such as sand and minerals, as well as the destruction of ecosystems. It also takes into account the transportation of these raw materials to the construction site.
The ICE database from Bath University contains all the information you need to understand the carbon footprint of construction materials. It has been downloaded by more than 30,000 professionals and appears in countless books, reports, articles and lectures.
Builders for Climate Action has compared upfront embodied carbon from various insulation types and found that using plant-based insulation, such as blown cellulose, can lower a building’s embodied carbon by a wide margin. By choosing insulation materials made from agricultural products that sequester carbon, such as wood or hemp, you can further reduce a project’s embodied carbon.