When you envision a green or sustainable building, what do you picture? For many, a high-tech building with gleaming glass and solar panels comes to mind. While this can be true, there are some other viewpoints on what makes a building sustainable. For me, the greenest buildings are the ones you don’t build. These buildings have built-in sustainability.
What do I mean by that exactly? What I mean is, by reusing our existing building stock instead of continually building new buildings, we are being inherently more sustainable and embracing the ideas of the green-building movement.
What most people fail to realize is just how much energy it took to create the materials that make up an existing building. When we study the science of embodied energy in a building, we start to realize how much effort it took for that building to exist. Calculating the embodied energy of a building takes into account the entire life cycle of a building from cradle to grave.
Embodied energy is the energy consumed by all the processes associated with the construction of a building, from the extraction and processing of natural resources, manufacturing, transport, construction, and ultimately the demolition of a building. Each of these processes uses varying amounts of energy, which contributes to the overall amount of embodied energy. To get a little geeky: Embodied energy is expressed in the unit MJ/kg or Megajoules per kilogram of the material.
So let’s look at an example of what we are talking about. To construct a building, we need materials. Raw materials need to be extracted from the Earth to make things like brick and concrete; clay needs to mined to make brick and some very energy-intensive processes are used to make cement and mine rock and aggregates, which are the components of concrete. These materials then need to be transported to the site requiring large trucks to consume diesel fuel to deliver the materials. Once we have the materials at the building site, the products need to be assembled and constructed, which also requires energy. The sum of all of this energy from extracting the materials from the Earth to erecting them onsite is the embodied energy of a building.
Demolition of the building in the future also needs to be considered. If we demolish a building and landfill all the materials, all of the energy expended to create, transport, and construct the building will be lost and the cycle starts over.
Not all building materials are created equally. Some materials, like aluminum (155 MJ/kg), have an extremely high embodied energy associated with the material. Bauxite, which is the main component of aluminum, is one of the most abundant elements on Earth. However, massive amounts of electricity are required to melt and refine the aluminum into a usable building product. Comparatively, stone and marble (2-4 MJ/kg) have a low embodied energy as we have relatively little energy involved in removing them from the Earth and preparing them for use. Mother Nature did most of the work for us.
The lesson to be learned here is that existing buildings are inherently more sustainable than their new construction counterparts. The reason being is that we are saving the embodied energy it took to create that building rather that wasting it by tearing the building down. So the next time you are considering building a green building, remember the inherent sustainability of our existing building stock.