We emit too much carbon. As I write this, the greatest nations in the world are addressing this issue by launching the G7 Industrial Decarbonization Agenda, committing to emission reductions in all sectors: power, transportation, agriculture, and building. The building sector represents 39% of these emissions. This number will only go up, with the building stock slated to double by 2060. To mitigate our carbon the way we need to, the American Institute of Architects (AIA) has recommended incremental steps toward carbon neutral buildings by 2030. This is usually accomplished in two steps: reducing operational carbon as much as practical, and producing enough renewable energy to take the remainder off fossil fuels.

Let’s start with Operational Carbon, which is what it takes to run a building. For every gallon of gasoline, kWh of electricity, or therm of natural gas used, there is an equivalent amount of carbon. Convert each of your energy bills to carbon, add that carbon up, and you have your operational carbon. A great way to reduce this number is to follow Passive House principles. By utilizing lots of insulation, airtight construction, and high-efficiency equipment; buildings of all types are able to drastically reduce their energy use, and therefore the carbon emitted. This is the most important and cost-effective step.

Then, you make sure the remaining energy used is not sourced from fossil fuels. Sources such as solar, wind, geothermal, hydroelectric, or biomass are all considered carbon neutral. The simplest solution (for the building sector) would be if the grid was 100% renewable, but that may not happen anytime soon, so most of us have to look at production on site for the moment. If you followed passive principles, then you likely just need to add solar panels to the roof to make up for the small amount of energy your project uses. If you don't have a renewable grid and cannot install renewables on site, you can install on another site you own, join forces with your neighbors, or buy Renewable Energy Credits (REC's). Some projects have a tougher time meeting this threshold than others, but the idea is to have enough carbon-neutral production to make up the difference. Homeowners, businesses, and even entire downtown districts in major cities are making the carbon neutral commitment. This is all very encouraging, but it's only half the picture.

Embodied carbon is what it takes to build a building, which may be as much as all the operating costs over the life of a building combined. Every wood stud, nail, brick, bag of concrete, and roofing shingle used on a project is extracted, manufactured, transported to the site, installed, maintained, and eventually replaced. The amount of carbon embodied in all that is assessed by a third party in what’s called an Environmental Product Declaration (EPD). Multiply each EPD by the amount of each product used, do this for each product, add it all up, and you have the project’s embodied carbon. We like to use a program called Tally in our office, which is connected to a reliable database of EPD’s and takes material volumes right off our virtual design models. Once you know your projects embodied carbon, you can use this materials palette to learn how to reduce it. You'll see familiar "soft" concepts have quantifiable advantages in your model: salvaging and reusing materials, using more wood, using less cement, using less XPS, using less PVC - it all suddenly makes a visible difference in a forehead-smacking proof-of-concept. The USGBC helped bring these calculations into the mainstream with the inclusion of a “Whole-Building Life-Cycle Assessment” as a credit option in LEED V4. With the characteristic rigor and reward a LEED credit brings, demand for this service is sure to follow.

If the project owns enough renewable energy to make up for both operational and embodied carbon - that is a true zero-carbon building. The AIA has set incremental thresholds towards carbon neutrality for us to follow, and a standardized reporting mechanism so we can share successful strategies along the way. We have a long way to go, but the path is clear, the demand is mounting, and we have all the tools we need to get the job done.

See you in the field,

Doug Shilo, USGBC NH Chapter Chair