Emissions from buildings are huge. These emissions come in two main flavors.
1. Energy emissions. These account for 25% of all global greenhouse gas (GHG) emissions and include CO2 that is emitted by directly burning fuel in buildings, as well as generating electricity for buildings by burning fossil fuels at power plants. In this article, we quote GHG emissions, which are more expansive than just CO2 emissions; percentages of GHG emissions may be lower, but more meaningful, than percentages of CO2 emissions.
CO2 represents about 75% of GHG emissions by warming equivalent. Other GHGs include methane, fluorinated gases (like what leaks out of air conditioners) and NOx compounds. Energy emissions sources include electricity for running appliances (8% of global GHG emissions), electricity for cooling space (2% of global GHG emissions), electricity and fuel for heating water (4% of global GHG emissions), electricity and fuel for heating space (8% of global GHG emissions) and electricity for lighting (3% of global GHG emissions).
2. Embodied emissions. These account for another 15% of global GHG emissions and come from making the stuff that goes into buildings. The major components include: the production of cement for buildings (5.5% of global GHG emissions), the production of steel and other metals including aluminum for buildings (3% and 1% of global GHG emissions respectively), the production of chemicals for insulation, fireproofing, waterproofing and other items for buildings (1% of global GHG emissions), and the production of the remaining building materials (4.5% of global GHG emissions).
All in all, buildings are responsible for 40% of global greenhouse gas emissions.
The Difficulties with Reducing Emissions
The only sure way to cut energy emissions is to use less energy.
Because renewable energy may provide abundant, low cost, albeit intermittent, clean electricity, there is a prevailing notion that the best way to reduce emissions is to electrify everything. While we generally support this trend, we also must admit that the future is a tricky thing to predict and currently, in most places in the world, electricity is more emissions intensive than direct natural gas per unit energy by a factor of about 2X. This means that in the present and in a possible future, electrified heat could be worse than natural gas heat.
The only sure way to cut embodied emissions is to not build things.
Building materials, especially structural materials like cement and steel, are difficult to replace because there are regulations and fear of the unknown. Additionally, no matter how good the lab data is, we do not know how new materials will perform in 40 years, 500 feet in the air until we take the risk and build the building. Because of this, even when we intend to use new “green” materials in buildings, conventional materials often get used.
How to Reduce Emissions
1. Remodel, reuse and do not build new buildings. The most sustainable thing to do is to not extract more resources from the earth, no matter how “green” the project is.
2. GHG emissions are a global problem, so find the data and consider global averages. The world average GHG emissions from the building sector per person is 2.8 tons of CO2 per person per year. Therefore, when we build a building, the total GHG emissions per occupant per year (including lifetime levelized embodied emissions) must be less than one-tenth of that number, or else the project is making the average problem worse. We chose one-tenth of the average because no person spends all of their time in a single built structure.
3. Existing and new buildings should maximize the occupants per square meter. This will minimize new construction (fewer buildings are needed if more people are in them). Designers and architects should be asking themselves: “How can we make a crowded space feel nice to space-hungry occupants?”
4. Use energy that cannot come from fossil fuels. Direct solar or geothermal lighting and heating and other non-grid and non-gas energy sources will always cut emissions, while electricity only sometimes will.
5. Use carbon negative building materials. Build as many structures as possible out of wood or other carbon negative materials like hempwool instead of conventional polymer insulation.
6. Reduce total energy consumption. Insulate, turn off lights, meter and reduce energy consumption below the global average.
7. If you must use conventional energy, use clean electricity. Try your hardest to ensure clean electricity by installing on-site solar or wind power with backup storage as needed.
About the Author:
Hugo Leandri is the CTO of Brimstone Energy, a startup spun out of Caltech which is working on the production of carbon negative, low cost, fully regulated ordinary Portland cement.