Sustainability
Julie Rapoport, Ph.D., P.E., LEED® AP
Building materials and climate change
Traditional masonry has a number of environmentally friendly characteristics, such as durability and thermal mass. However, as our collective understanding of environmental science and especially of climate change advances, we’ve had to revise our definition of green building. The manufacture of building materials (concrete, clay brick, gypsum wallboard, steel, etc.) accounts for about 12% of all emissions of carbon dioxide (CO2)-a greenhouse gas with an immediate and direct impact on climate change.
CO2 and embodied energy
One increasingly useful way to measure a product’s environmental impact is to audit its ‘embodied energy’ and ‘carbon footprint’—the amount of energy consumed and CO2 released in the extraction, processing and transportation of raw materials and manufacture of the finished product. One focus of materials research and development is finding ways to reduce the environmental footprint without sacrificing other product benefits.
Why firing brick emits lots of CO2
Clay brick is high in both embodied energy and carbon footprint. Clay brick manufacturing is energy-intensive because clay requires firing for up to three days to become hard and durable. Brick firing kilns operate at about 2,000 degrees F and are generally kept hot even when not in use. The heat for most kilns is generated by burning natural gas, while some brick producers use fuels such as coal and petroleum coke that emit even more CO2 than natural gas does. All of these fuel sources emit significant CO2 during combustion.
Calculating the impact
The National Institute of Standards and Technology (NIST) Building for Environmental and Economic Sustainability (BEES) database lists the average embodied energy for a common fired clay brick at 8,800 BTUs. The Brick Industry Association (BIA) notes that a clay brick plant operating at optimal efficiency might reduce this figure to 5,000 BTUs. For purposes of our calculations, we have chosen a middle ground of 6,000 BTUs of embodied energy. CO2 emission is often a by-product of energy consumption; each clay brick fired with fossil fuel conservatively releases 0.9 lbs of CO2 into the atmosphere.
The CalStar brick solution
At 7 billion bricks used per year in the US alone, the brick market is primed for innovation.
Producing brick from recycled fly ash consumes less energy and emits less CO2 because it does not require firing to harden the masonry units. Nor is any cement, which also has a large carbon footprint. As a result, the CalStar green brick solution represents 85% lower embodied energy and 85% lower CO2 emissions than traditional fired clay brick.