Responsible for nearly 40 percent of global climate emissions, buildings are critical to the government’s response to climate change. As lawmakers and climate advocates look for new policies that will curb greenhouse gas emissions from the built environment, the old rallying cry for energy efficiency is being replaced by calls for policies that drive building decarbonization. This leads to the question, just where does energy efficiency fit in this broader goal of decarbonization?
Embodied vs. Operational Emissions
Whole building decarbonization requires tackling both a building’s embodied carbon emissions and its operational carbon emissions.
Operational carbon refers to a building’s energy requirements for heating, cooling, lights, and plug loads. This is where low carbon sources of power (wind, solar, hydro, nuclear, and “green” gas) can play a part in reducing the emissions required to operate the building.
Embodied carbon consists of three primary categories: initial embodied carbon, recurring embodied carbon, and end-of-life embodied carbon. For example, the refrigerants used in a building’s air conditioning system are a significant contributor to a building’s carbon emissions. They need to be accounted for as refrigerants leak, require replacement, and will eventually need to be properly disposed of.
Additionally, while renewable sources of power are generally considered not to have direct emissions, they still have embodied carbon to account for. The manufacture of solar panels, batteries, and wind turbines is an energy-intensive undertaking, as is maintenance, replacement, and disposal of the equipment. They are the same as virtually every material and product used in the construction and operation of a building in that carbon emissions are generated in their manufacture, delivery, and installation. That’s embodied carbon.
Smart Policy Recognizes the Importance of the Building Envelope
Building envelope efficiency is the vital link between building embodied and operational decarbonization. A highly efficient envelope means the building will require less generation (green or otherwise) and maintain occupant comfort using smaller HVAC systems. Recent studies also highlight the positive impact efficient building envelopes play in passively managing peak heating and cooling loads in buildings. This will be increasingly important as the world shifts to solar and wind electricity.
Approximately 20 years ago, California established a “loading order” to guide the state’s energy policy decision-making. That order calls for pursuing cost-effective efficiency resources before investing in renewable energy sources to meet the state’s energy demand. It makes sense to apply the same loading order to decarbonization policies focused on the built environment.
The Importance of the IECC
The policy tool available for constructing buildings with highly efficient building envelopes is the 2021 International Energy Conservation Code (IECC). The residential and commercial envelope requirements in the 2021 IECC have been found by the U.S. Department of Energy to be cost-effective and offer the blueprint for achieving substantial carbon reductions in new buildings right now.  
The first focus of residential building decarbonization must be on requiring all homes built in the U.S. to meet the building envelope requirements of the 2021 IECC. Nearly half of the states remain stuck on the 2009 IECC. That means nearly 600,000 homes built each year are built with building envelopes that are about 30 percent less efficient than the 2021 IECC.
There are many policy levers available to ensure that new homes are built to the 2021 IECC. Aside from state adoption of the updated energy code, the Federal Housing Administration can require 2021 IECC compliance for new homes purchases with government mortgage products. In addition, the EPA can make the 2021 IECC building envelope requirements a component of the ENERGY STAR® Single-Family New Homes Program. These updates would send a strong signal that this administration is serious about decarbonizing our nation’s buildings.