Food pyramids are simple visual guides to the types and proportions of food that we should supposedly eat, in order to stay healthy. Can we apply a similar principle to our buildings? Can we build a Construction Material Pyramid based on the environmental impact of materials used to build them?
The Construction Material Pyramid
That’s exactly what the Construction Material Pyramid hopes to achieve. It was developed in 2019 by the Center for Industrialized Architecture and Hennig Larsen architects. The pyramid highlights the environmental impact of the most used construction materials like structural steel, aluminum, double and triple paned windows, insulation, lumber and more. Data driving this pyramid is based on extraction, transportation and manufacturing. It does not take performance and lifespan into account.
Impact Categories
This interactive version of the material pyramid allows you to toggle between 5 impact categories.
1. Global Warming Potential (GWP) or Carbon Footprint
The first is the global warming potential or carbon footprint. GWP calculates how much heat is absorbed and trapped by a certain amount of gas, compared to carbon dioxide. The higher the value of the GWP, the greater the impact on our environment. Metals like aluminum, steel, copper and zinc occupy the highest level, while wood products have negative rates. They absorb more greenhouse gases than they produce during their manufacturing.
2. Ozone Depletion Potential
The second is the ozone depletion potential. During manufacturing, materials release certain gases that can degrade the ozone layer. When a single chlorine or bromine atom comes into contact with ozone in the stratosphere, it can destroy over 100,000 ozone molecules. This decreases protection from the Sun’s ultraviolet radiation, it affects flora and fauna and can even increase the risk of skin cancer. Polyiso and polyurethane foam insulation are the most harmful, while materials that require low processing, like bricks and aluminum sheets are the least harmful. However, it’s important to note that the new versions of spray foam have reduced the ozone depletion potential by 99%. We discussed in my video on open and closed cell foam. Spray foam no longer uses hydrofluorocarbon or HFC blowing agents. They use hydrofluoroolefin or HFO agents.
3. Photochemical Ozone Creation Potential
The third is photochemical ozone creation potential. Some materials produce carbon monoxide, nitrogen oxides and volatile organic compounds during manufacturing. When sunlight hits these compounds, they form ground level ozone which can affect our health. High levels of O3 can disrupt ecosystems and cause eye and lung irritation. Metals and vinyl flooring are the main culprits, while wood based materials are the safest.
4. Acidification Potential
The fourth is acidification potential. The extraction and production of some materials release sulfur dioxide, nitrogen monoxide and nitrogen dioxide into the air. They react with water, oxygen and other chemicals to form sulfuric and nitric acids, which can fall to the earth as acid rain. Paints and linoleum have a much higher acidification potential than straw and rammed earth.
5. Eutrophication Potential
Lastly, is eutrophication potential. An unnatural increase in nutrients like nitrogen and phosphorus in water starts a process called eutrophication. Algae feed on the nutrients, growing, spreading and turning the water green. In large concentrations, these compounds can lead to algal blooms, tainted water supplies and the death of fish. Steel production emits large amounts of nitrogen oxides compared to clay bricks.
Materials Featured in the Construction Material Pyramid
The Construction Material Pyramid allows designers to quickly understand the impact of building materials. It reminds us that we should place value on the bones of buildings, not the stuff that we fill them with. It also reminds us that the building materials we choose have a huge impact on our environment, whether positive or negative. Let’s talk about 3 materials that are featured in the construction pyramid. We’ve touched on them in previous videos, but they deserve more explanation.
1. Structural Steel
Steel production is energy intensive and one of the leading sources of greenhouse gases. Nearly two tons of carbon dioxide are emitted for every 1 ton of steel produced. It also accounts for five percent of total greenhouse gas emissions. But it isn’t fair to only highlight the negative aspects of this material. Steel is essential to building wind turbines, electric vehicles, and mass transit systems; all the infrastructure required in a low-carbon economy that isn’t reliant on fossil fuels. To everyone that gave me hell for saying that building with wood is more eco-friendly than using new or one-time use steel shipping containers, look at the numbers.
2. Cross Laminated Timber (CLT)
Engineered wood like glulams, cross laminated timber and laminated veneer lumber have the potential to revolutionize the building industry. To improve the properties of wood and make it even stronger than steel and concrete, layers of wood are sandwiched with moisture resistant glues and compressed under heat and pressure. Even though engineered wood is made of fast growing trees and not hardwood trees from the rainforests, we must use only sustainably sourced wood. Responsible forestry practices involve planting a tree for every one cut down and avoiding mass clearing of forests.
3. Concrete
The data on concrete really surprised me. Worldwide, we use about 30 billion tonnes of concrete a year, which accounts for 8% of global carbon dioxide emissions. When I was researching concrete for my video on geopolymers, every article and paper claimed that concrete was one of the most polluting materials, but it ranks lower than steel in every category! The manufacturers of cement and concrete now use recycled waste like fly ash which can drastically reduce its carbon footprint. Holcim, a Swiss cement manufacturer, recently published a sustainability report which explained their path to zero carbon cement. I’ll link that report in the description if you’d like to read it. I’m going to interview the person who wrote the report next week, so if you haven’t subscribed to my podcast channel yet, check it out after this video.
Conclusion
I think that the takeaway from the construction pyramid is that materials like concrete, steel, and glass have allowed us to tame nature and push the limits of engineering but their extraction and production come at a cost. It’s important for us to be aware of that cost and, if possible, choose alternatives that are not as harmful to the environment. I’d also like to point out that material scientists are constantly working to improve manufacturing processes and the performance of the materials. I’d expect the data on the material pyramid to change every year.
