When it comes to reducing emissions that contribute to climate change, the combination of renewable energy and natural building materials offers an affordable, achievable, and effective solution.
Reducing construction industry greenhouse gas emissions has focused on the energy efficiency of buildings, by reducing the energy used to heat, cool, and power each building. This focus makes sense, as the energy-related emissions over decades of building use are an obvious target.
However, two critical factors are often overlooked: the emissions of the energy source and the embodied emissions in the building materials—from raw materials extraction to manufacturing. Unlike “fuzzy” targets for energy efficiency—which depend on the quality of construction and occupant behavior for any degree of success—these are measurable factors that can be guaranteed to have the desired effect.
Using renewable energy has immediate and measurable impacts in offsetting carbon dioxide and other greenhouse gases. Less understood is the embodied carbon footprint of building materials, including construction materials intended to decrease energy use. Ironically, high-carbon-emitting materials are often used to save energy and carbon.
Consider the carbon footprint of different insulation materials (see “Materials” table), some of which have a very high carbon footprint. For example, a conventionally constructed, 2,000-square-foot house insulated with fiberglass batts in the walls to achieve R-28 will be responsible for 1,750 pounds of carbon emissions. The same house that uses extruded polystyrene foam insulation in the walls has a carbon tally more than double that, at 3,820 pounds. That home could have been built with straw bale walls, which have a carbon-sequestering effect and would have removed 4,245 pounds of carbon from the atmosphere—where it remains in the home’s walls.
Sequestering with Straw
Here’s how a construction material can be carbon-sequestering: The cellulose of all plant-based materials is composed of a high percentage of carbon (ranging from 37% to 55%, depending on the plant and the growing conditions). This carbon is “digested” from the atmosphere as the plant grows. When that plant material decomposes (or is burned), most of that carbon returns to the atmosphere. However, when straw or other plant material is used in buildings, it is removed from the atmosphere for decades or even centuries, reducing the overall amount of carbon in the atmosphere.
The minimal amount of carbon emitted in the straw harvesting and manufacturing is vastly surpassed by the amount sequestered in the material itself. If straw is used instead of foam, the overall effect is 8,065 pounds of carbon reduction for just one 2,000-square-foot home. Multiply that by the 740,000 single-family residences built in the United States in 2015, and that would have been a whopping 3 million tons of carbon reductions.