More and more, green builders and architects are looking to reduce embodied carbon, and when possible, store it in buildings, says Marc Rosenbaum, instructor of HeatSpring’s Zero Net Energy Buildings course.

“We’re changing our view from net zero energy buildings to net zero carbon or even carbon positive buildings,” he says.

Embodied carbon data focuses on the emissions footprint associated with harvesting, transporting and manufacturing building materials. It’s possible to calculate the embodied carbon by obtaining an environmental product declaration (EPD) from building material manufacturers. 

Calculating Embodied Carbon

Embodied carbon is usually expressed in equivalent kilograms of carbon dioxide per defined unit of product or material. The Carbon Leadership Forum offers a tool for calculating embodied carbon and the Builders for Climate Action plan to offer a calculator.

Materials based on plants or waste streams can store carbon in buildings, says Rosenbaum. With such materials, a building can become a carbon sink.

Different Insulations Yield Different Carbon Footprints

One example is insulation, which is available in numerous materials that have a range of different impacts on a building’s carbon footprint.

Due to the blowing agents used, some types of spray foam insulation have a high global warming potential. On the other hand, cellulose insulation, if it comes from a waste stream such as newspaper, removes carbon from the atmosphere and stores it in buildings, says Rosenbaum. If not used in a building, the cellulose would go to a landfill, where it would decompose, emitting carbon into the atmosphere.

When straw is used in straw bale buildings or in insulation panels, it doesn’t get burned in the field. It becomes a structural component of a building, storing the carbon and avoiding emissions. Another example is hempcrete, an alternative to concrete, says Rosenbaum. It locks carbon in the material–more than was used in its production and use.

Classic Indigenous Buildings Store Carbon

“Traditional indigenous buildings are carbon positive,” says Rosenbaum. “They are generally some combination of mineral and plant, with clay and mud. This gets you to a building that is storing a lot of carbon.”

While the green building industry is focusing more and more on carbon positive buildings, zero net energy buildings can play an important role in this movement, notes Rosenbaum. That’s because they use less energy.

Where Do Zero Net Energy Buildings Fit in?

Buildings constructed to traditional codes draw more from the electrical grid for energy, which has carbon emissions associated with it, especially if the grid relies on coal or natural gas. Zero net energy buildings don’t draw as much from the grid because they’re energy efficient and often include renewable energy.

But the grid is getting cleaner. A grid based on 100% renewables, for example, would contribute less carbon than today’s grid, he says. That’s good news. For that reason, designers’ focus has transitioned from the operational emissions to the emissions embodied in the building’s construction.

Also good news is the fact that information available about the embodied carbon in building materials is becoming more widely available.

“Most of us as practitioners are just learning how to use this information. Literally five years ago there was little readily accessible information,” says Rosenbaum.

Embracing Humility and Courage to Address Climate Change

Manufacturers now provide this information based on calculations performed in accordance with internationally accepted protocols. EPDs are available for materials like softwood lumber, plywood, spray foam and cellulose. But the process of identifying embodied carbon keeps evolving.

“We are really dedicated to learning more and getting better. Everything we learn complexifies the problems we are trying to solve. It takes humility and courage to keep moving forward and building, knowing that you won’t do it perfectly,” says Rosenbaum.