Grey energy

-If we start building only from wood we will cut down all the forests and nothing will be left? That’s why you have to build with concrete … or plastic.

Such statements are often said by (unaware) professionals during meetings, lectures or workshops that I lead. They expose a big knowledge shortfall regarding materials’ environmental impact, though there are multiple aspects to be tackled to avoid unnecessary reductionisms. First off, timber is a renewable source and concrete and plastic are not. Secondly, the question departs from the idea of constant growth, the concept of the contemporary world and the major economies. Indeed, if we are constantly looking for more and more, even timber buildings, or any other ‘eco-material’, will not eliminate the negative impact of construction on the environment. Society operates within the planetary boundaries and the environmental capacity. Exceeding them to have more or to build more has led us to a catastrophe that is on the horizon.

Following the principles of degrowth, before a project is born, two questions must be answered ‘where?’ and ‘what for?’ we are building. Only then ‘how?’. Only thena designer should answer the question ‘what to build from?’. Giulia Sonetti, from the Polytechnic University of Turin, says that the best energy is the energy that we do not consume. Degrowth is a reminder to use materials responsibly and where needed. Does your community need another mall? What is the purpose of the next science and technology park or organic nutrition research centre? Empty buildings are just expensive scenery in the city, with no inhabitants and no purpose from the very beginning they cannot be sustainable.

Energy may be grey

The energy that an energy-efficient building consumes throughout its life is mostly used for its operation. In low-energy buildings it is as much as 60% [1]. The remaining 40% is energy that is needed to obtain the elements of a building, including materials for floors and ceilings, lamps, ventilation system, slab on the terrace, and handrails. And it is important to ponder about this forty percent. Forty percent that is often forgotten. Embodied energy is energy, sometimes called grey, consumed in processes related to the production, transport and delivery of products to the consumer. This approach brings us to the idea of Life Cycle Assessment.

In the life cycle of a material, we can distinguish four stages:

  1. Raw material preparation. Extraction from the ground (inorganic materials) or harvesting (organic materials), cleaning, melting or other preparations. The energy cost of this phase also includes the transport of raw materials from the place of origin to the place of production.
  2. Production. When raw materials are processed into products (windows, tiles or door handles). The energy costs of a project should also account for packaging and further transport to the user.
  3. Operation. If the product needs energy (e.g. a radiator or lamp uses energy in order to function)
  4. Disposal. Composting or further life. This stage involves preparing the material for further life, disassembling it into parts, and processing it.

The sum of these energies corresponds to the whole life cycle of the building. By adding up the amount of energy that a building consumes during its operation and its grey energy, we can evaluate to find the best energy strategy. The simplest way to reduce the total consumption of grey energy is to build durable and to treat each element with attention.

construction site = energy storage

Reusing, recycling, upcycling.

According to scientists from Stanford University [2], reusing building materials saves up to 95% of grey energy that would otherwise be wasted. However, some materials such as brick, tile, and cladding stone can be damaged during demolition and it may be difficult or impossible to use them in a new context. Depending on the material, reusing it can bring various savings (this is mainly due to the processing process), In the case of aluminium it can reach as much as 95% and in the case of glass 20%. Moreover, some processes may use more energy than new materials, especially when transporting over long distances.

The most complex topic is upcycling, which seeks to preserve the value of a material. Again, depending on the material, such a process may or may not be expensive in terms of energy. In a typical situation, the glazing remains glazing, and the handrail is a handrail because the amount of energy needed to produce such an element for operation is so high that its function should not be changed. From an energy perspective, this process appears to be the most efficient as we do not alter the properties of the materials. This topic is also related to the concept of Buildings as Material Banks, where all the buildings and their elements are seen as repositories for future buildings. Where all buildings are designed for disassembly.

To maximize the positive impact of a building on the environment, it is crucial to assess the amount of energy it consumes over its whole life cycle, from sourcing materials through functioning to the next life of materials. Knowing the relationship between how a building works, consuming 60% of energy, and where it comes from, we can plan and design more responsibly.

Adrian Krężlik


[1] Thormark C., “A low energy building in a life cycle — its embodied energy, energy need for operation and recycling potential”, Building and Environment, vol. 37, no. 4, (Apr. 2002), pp. 429–435.


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