Home 9 Magazine 9 Future of Real-Estate 9 Gray energy: How do construction materials influence the sustainability of buildings?

Gray energy: How do construction materials influence the sustainability of buildings?

Autor: TWINGINE editorial staff

10 Min.

Since the energy transition at the latest, green energy has become a term familiar to a great many people. But what is "gray energy"? And why do building owners need to take a closer look at this particular form of energy? Here are the key facts at a glance – and efficient ways to optimize them using TWINGINE.

What is “gray energy”? Definition and examples

Buildings consume energy. Buildings consume energy. required for air conditioning and heating systems in buildings can be easily determined by looking at the consumption costs. However, there are a lot more energy consumers in buildings than just the heating and lighting systems.

We are talking about all the products needed to construct and equip buildings. The primary energy required to produce the raw materials, construction components, and other materials is known as gray energy.

Gray energy can be calculated with the help of data sets on the carbon footprint of construction materials, the construction process itself, transportation, energy, and disposal. ÖKOBAUDAT, for example, provides these types of data.

Examples of gray energy

Gray energy is inherent at every stage of a building’s life cycle, i.e. construction, operation, and even in the dismantling process.

These stages include:

  • Processes required to produce raw materials
  • Vehicles that transport construction materials to the site
  • Machinery used to process raw materials into construction components
  • Construction site operation
  • Storage and disposal of construction materials
  • Services related to the sale of construction materials

Concrete is a particularly clear example of why it is important to be aware of the environmental impact of construction materials. Concrete is made from a mixture of aggregates and water, using cement as a binder. However, temperatures of over 1,400°C are needed to make the cement.

In fact, one tonne of cement generates almost one tonne of carbon emissions during the manufacturing process. The Intergovernmental Panel on Climate Change estimates that around three billion tonnes of carbon emissions are generated each year through the production of cement – that’s almost ten percent of all carbon emissions worldwide.

What does gray energy mean for the sustainability of buildings?

Even though the carbon footprint of cement exposes it as a genuine climate killer, concrete is still one of the most widely used construction materials worldwide, as it is inexpensive, easy to work with, and very stable. However, so far the gray energy associated with concrete has hardly been a factor in the question of how sustainable buildings really are.

Instead, the carbon footprint of buildings is usually measured solely by their energy requirements during operation. The use of renewable sources of energy and efficient air conditioning systems can help to positively impact the energy efficiency of buildings. However, in most cases, measures of this kind can do very little to offset the proportion of gray energy in concrete buildings.

New vs. existing buildings: Which of these are responsible for more gray energy?

Although existing buildings are often demonized today as wasteful polluters and energy guzzlers, a new building is not necessarily the more sustainable alternative. Many existing buildings have been constructed to last for a very long time. The longer they remain in use, the smaller their carbon footprint is compared with new buildings.

To assess the sustainability of a building, its entire life cycle needs to be taken into account, as by definition, sustainable behavior demands the careful use of resources – and that applies to every single brick that goes into making a building.

The German Federal Environment Agency’s publication “Energy Consumption for Building Concepts Across the Entire Life Cycle”, for example, provides a number of approaches to this issue. The study examines the consumption of energy across the life cycle of various types of residential building.

How can the gray energy used to construct a building be reduced?

Gray energy is an important factor in every phase of a building’s life cycle. There are therefore various ways of optimizing the “indirect” energy consumption of construction materials, from the construction phase through to operation and ultimately dismantling. The following examples show some possible approaches to this issue.

Constructing a new building: Compare construction materials

When constructing a new property, building owners can have a direct impact on gray energy by selecting the right materials from the outset. Obviously, the materials selected need to meet the technical and aesthetic requirements of the project in question, but other factors such as origin and longevity also play a significant role.

Whenever building owners have a choice between various construction materials, they should compare the available information on the production and origin of those materials. For example, regionally grown and processed timber generally requires less energy to produce, transport, and dispose of than imported cement.

The amount of gray energy that wood can save: A study conducted by the Federal Institute for Research on Building, Urban Affairs and Spatial Development found that the use of wood can reduce the carbon emissions generated when constructing a building by 40 to 60 percent.

Operation: Renovation is better than construction

In Germany alone there are 19.3 million residential buildings, plus commercial real estate. According to the German Sustainable Building Council (DGNB), one third of all greenhouse gas emissions generated by a building occur during the production and construction stages. Every existing building that is renovated saves gray energy that would otherwise be required for a new building.

But is renovation worthwhile if, for example, new insulation material has to be produced for it? The Forschungsinstitut für Wärmeschutz e.V.München (research institute for thermal insulation) has calculated that the amount of thermal energy saved is greater than the gray energy required to produce the thermal insulation material, which means the gray energy is compensated for within one winter heating period.

Dismantling: Turning old into new

The construction industry is one of the most resource-intensive economic sectors in Germany. In 2019, a total of 416,536 tonnes of waste was generated within the country – 230,851 tonnes of which was construction and demolition waste.

For this reason, the Federal Environment Agency makes the following recommendations:

  • The generation of construction waste can be avoided by preserving existing building substance and designing building structures for a long lifespan.
  • If building design, site operations, and demolition are planned with recycling in mind, any unavoidable waste can be retained within the economic cycle.
  • If construction and demolition waste has to be disposed of, it should be limited to what is unavoidably necessary and disposed of as ecologically as possible.

One way of dealing with construction waste in a sustainable way is to process it into recycled construction materials. If the recycling is done on site, there are attractive opportunities for building owners to build sustainably. Pilot projects of this kind already exist, for instance in Munich.

With recycled materials obtained from a construction site nearby, building owners can also make themselves less dependent on the raw materials market, which is still struggling with supply problems due to the corona crisis.

Using digitalization to build more consciously and reduce gray energy

According to the association “Bauwende”, the key to sustainable construction and reducing gray energy is life cycle analysis. However, to keep track of all the data, compare different construction materials directly, and make the best decision for their project, building owners need state-of-the-art software tools.

TWINGINE analyzes various building models, taking essential factors such as cost, quality, and sustainability into account. The Building Model Analyzer provides life cycle simulations that get the most out of operating buildings.

Moreover, CAPEX simulations make it possible to identify the most effective levers in the choice of materials, such as for the façade. In doing so, TWINGINE makes use of market standard and individual cost databases as well as carbon emissions databases.

Discover the options TWINGINE offers building owners for analyzing sustainable real estate projects and contact us to arrange an individual demo right now.

Your professional insights into the real estate industry

What benefits does BIM offer in real estate projects? How do digital twins support building developers? How do real estate professionals make more efficient use of BIM data? The e-book BIM in Practical Use provides answers.

Written by:

TWINGINE editorial staff

Discover our Magazine.