Embodied Carbon

Buildings contribute to the climate crisis in three distinct ways.  1.  Upfront  embodied-carbon- emissions: those arising from the collection, fabrication, and transport of building materials.  2.  Building operation emissions:  the daily energy consumption reflected in utility bills (energy efficiency).  3.  Energy profile emissions:  the kinds of energy used in operations (gas, propane, electricity).

The term “energy efficiency” can be a source of misunderstanding when it comes to climate change: energy and heat-trapping gases are neither synonymous nor equal.  To slow global warming we need to be mindful of CO2 emissions rather than focusing solely on energy use.  Energy-savings are one consideration in an overall strategy for reducing carbon emissions, but it alone is insufficient to alleviate rising emissions.

Habitable Designs addresses this concern by performing lifecycle analyses of structures. Carbon emissions can be minimized over a building’s lifetime by incorporating savings from all three emission sources noted above.  With legacy-style construction, upfront embodied emissions dominate the building’s carbon footprint for its first 10-12 years.  Even after 50-years upfront emissions persist in the atmosphere and remain a significant contributor to the building’s lifecycle carbon footprint.  Incorporating biogenic building materials throughout the structure starkly reduces upfront emissions.

Legacy materials exhibiting high-upfront embodied-carbon content include steel, Portland-cement concrete, fiberglass-insulation, as well as polystyrene & polyurethane (spray foam) insulation.  Materials with low-upfront embodied-carbon are almost exclusively biogenic in origin, because they sequester atmospheric carbon while growing.  Moreover biogenic materials need minimal processing to be transformed into structural elements or insulation.

Shown below are four types of insulation materials and/or structural elements along with their embodied-carbon content, in units of (equivalent) pounds of CO2 per pound of installed material. Positive numbers indicate a release of CO2 to the atmosphere during product fabrication while negative shows a net absorption (or drawdown) of CO2 from the atmosphere after installation.

Extruded polystyrene (14,700 lbCO2e/lb)

Expanded polystyrene (1850 lbCO2e/lb) credit: CanPHI

Spray foam (3300 lbCO2e/lb)

Integrated biogenic wall (-22,000 lbCO2e/lb) credit: CanPHI

Because homeowner health is also important to household comfort, Habitable Designs avoids products with Red List chemicals (products known to have egregious side-effects).  One example is formaldehyde out-gassing.  The entire Red List can be found under ‘Links’.