The “carbon balance” of a building is made up of its base emissions minus any carbon reduction actions taken, including any offsets purchased and applied to the building. Our model works for both new and existing buildings, from construction to operation and maintenance, to end of life (encompassing lifecycle modules A1-A3 and B2-B6 on an LCA).

Base emissions consists of two components:

• Embodied carbon refers to the collective carbon emissions from the construction of a building and the materials in it. This includes all the carbon it took to build that structure, renovate it over time, and then demolish it when its lifecycle ends.
• Operational carbon refers to the emissions from its ongoing energy use as part of operating it: electricity, heating and cooling, water, and so forth. 

The building’s base emissions are estimated using multiple data points, the three most important of which have the greatest impact on any building’s carbon footprint:

• Structure type. The foundational materials of a buildingFor example: wood, mass timber, concrete & steel.
• Primary usage. A residential building typically requires much less energy to operate than a hospital, for example. 
• Location. Our model takes into account regional differences in building materials, the percent of renewable energy available on the local energy grid, and other factors. Different geographies also experience different weather patterns with corresponding peaks and valleys in typical energy usage.

Additional data points that factor into the estimation to a lesser degree:

• The building’s age. Older buildings have a better embodied carbon estimate because a long-standing building has captured carbon for a longer period. To account for this, we depreciate the embodied carbon over a 60-year timeframe.
• Size in terms of total square feet. We also provide the estimate of base emissions by square foot, helping to compare the carbon “efficiency” of buildings which vary greatly in size.

The chart below illustrates how each factor influences carbon balance totals for two representative buildings: a two-story, single-family residence and a larger office building, both built in the same year. As you can see, each building’s carbon balance varies significantly based on geographic location. You can also see how the structure & size of the building impacts its embodied carbon emissions when the location changes. Lastly, you’ll note that when you look at a building’s carbon emissions by square foot, even large concrete & steel buildings can be as efficient as a small woodframe home.

For more technical calculations, please see our scope and methodology knowledge base article.