Decarbonizing Buildings: A Changing Lexicon

From kilowatts to carbon, the language we use matters. Building sector policies and programs across the nation are in the midst of a critical shift from delivering energy efficiency in terms of kWh, to policies and programs that seek carbon emissions reductions and even carbon neutrality. With these changing tides, it is becoming apparent that there is need for a new, shared lexicon around what it means to design, construct and operate buildings that use little or no energy and contribute little or no carbon emissions.

Terms such as “zero energy,” “zero carbon,” and “carbon neutral buildings” are already being integrated into public policy (climate action plans and energy plans), but with a great deal of uncertainty around what they mean. Lack of clarity in definitions makes it difficult to pinpoint what problems we are solving for and what metrics we are using to measure progress. What’s more, future growth of solar and other renewable resources supplying energy to buildings will further muddle the present correlations between better building efficiency and resulting carbon mitigation.

What follows is a summary of NBI’s perspective on applying the new, emerging lexicon around low-energy and decarbonized buildings that is spanning the energy, regulatory and environmental ecosystem. This is by no means comprehensive, but intended to be a starting point in our future dialogue.

Zero Energy, Net Zero Energy, Zero Net Energy

A zero energy building combines energy efficiency and renewable energy generation to consume only as much energy as can be produced onsite through renewable resources over a specified time period. (Source: U.S. Department of Energy)

DOE released this description in 2015 as the official federal definition of zero energy. However, there continues to be lengthy–bordering on philosophical–discussions about what should be the objectives and outcomes of zero energy buildings. There are questions about whether renewables need to be onsite or can be nearby, if campuses or districts count as one project with a common generation source or individual buildings, etc. These questions arise as the marketplace becomes more sophisticated about developing and delivering zero energy buildings and projects become more complex.

Currently, a building designated “zero energy” produces an equivalent amount of its energy onsite, using renewable sources such as solar or wind. At times, this building will produce more electricity than it needs, feeding that extra power back to the grid (net-metering) or storing it in batteries onsite. Any power this building needs during times when onsite renewables are not producing comes from the grid. Over a 12-month period, the total net energy used by the building from offsite resources would be equal to or less than what the onsite renewables produced.

Terms vary from city to city and state to state and you will hear both “zero net energy” and “net zero energy” applied synonymously. With today’s emerging focus in carbon, you will also hear “net zero carbon” referred to in relationship to net zero energy. However, net zero energy and net zero carbon are not the same. Currently, a net zero energy building does deliver significant carbon emissions reductions, but not necessarily zero emissions.

Zero Carbon, Net Zero Carbon and Carbon Neutral

A zero carbon building is defined as one that is highly energy-efficient and produces onsite, or procures, carbon-free renewable energy in an amount sufficient to offset the annual carbon emissions associated with operations. (Source: Zero Carbon Building Standard Canada Green Building Council)

The purpose of the three terms is to describe a net-carbon balance for a building’s operation over the course of 12 months. They are generally used interchangeably. Sometimes the term “zero emissions” is used synonymously with zero carbon, however these are not the same. Like a zero energy building, a building designated “zero carbon” is highly energy efficient and produces an equivalent amount of its energy on-site, using solar, wind or other renewable sources.

Any energy demand that can’t be produced onsite must be procured from qualified off-site renewable energy sources. The environmental attributes of that power, usually in the form of Renewable Energy Credits (RECs), must also be contractually secured on behalf of the owner or tenant. This aspect acknowledges the limitations of onsite generation and allows for the use of qualified alternatives. These requirements are currently being defined in national building codes such as ASHRAE’s 189.1.


Electrification refers to replacing direct fossil fuel use (e.g., propane, heating oil, gasoline) with electricity [use] in a way that reduces overall emissions and potentially energy costs while lowering other air pollutants. (Source: Environmental and Energy Study Institute)

Electrification of a building’s space and water heat system might mean switching from heating systems that use natural gas, propane or oil (even wood) to electric heat pumps. The definition above states that electrification potentially reduces energy cost because cost reduction may not always be the case and is not a pre-condition for electrification. Some building owners will electrify even if the energy cost is initially higher as a way to achieve other goals or benefits. This also points to the fact that in some areas utility rates are such that the onsite combustion of fossil fuel-based power is cheaper than electricity.

There is a strong connection between zero energy buildings and electrification. The vast majority of the verified zero energy commercial buildings in NBI’s Getting to Zero Database are electrified. Why is this important? Many macroeconomic and electricity planning studies indicate that deep economy-wide carbon goals (e.g. 80 percent reduction in carbon emissions by 2050) cannot be realized unless a large portion of direct combustion in buildings is electrified.

Some policymakers are pursuing the electrification of a large percentage of the 70 million buildings that currently burn fossil fuels for heating in order to help lower both carbon emissions and local air pollutants while improving indoor air quality. The attributes of site fuel combustion on occupant health is another topic that is increasing the focus on electrification.

Building-Grid Integration, Grid-Enabled Buildings, Grid Harmonization

Building-grid integration refers to the integration and optimization of homes and commercial buildings with the nation’s energy grid. (Source: Department of Energy)

Buildings that generate or procure enough renewable energy, often through solar panels, to offset their entire annual energy consumption create a situation where their demand for electricity during a day, week or year differs from when electricity generation is being supplied by onsite or grid-delivered renewable energy. The unaligned timing of electricity demand load and generation can place extra strain on the electricity grid.

Building-grid integration relies on sensors, control systems and other technologies that work together to manage energy use and to shift loads to meet specific objectives. These technologies may coordinate electricity generation and consumption onsite, and they can improve efficiency, work to reduce carbon emissions, and mitigate the burdens on the nation’s electricity grid. Battery storage is another rapidly evolving technology that could improve interactions with onsite renewables and/or the grid by storing electricity during peak generation and discharging it during peak demand.

Applying Definitions

Without federal leadership around climate change policy, jurisdictions are setting their own varied climate goals and instituting the strategies underlying the meanings of these interrelated but nuanced terms. NBI is currently working with policy writers in many cities and states to create more clarity around the terms as well as defining metrics to ensure that policies drive the intended changes within the marketplace.

In our next blog, we’ll focus specifically on how we’re using these definitions to describe the underlying foundations needed for successful building policies to achieve jurisdictional climate goals for the building sector.

Written by: Jim Edelson, Director of Codes & Policy