When people talk about climate protection in the construction sector, they often think first of thermal insulation, solar power, or energy-efficient new buildings. Yet one crucial factor is often overlooked: what is known as “gray energy.” It is already present in every building—in the building materials used, their manufacturing, their transportation, and their installation. Historic buildings, in particular, therefore have enormous ecological value. Preserving them conserves resources, avoids CO₂ emissions, and makes an important contribution to sustainable construction. Old buildings are thus far more than mere testimonies to past architectural traditions—they can become true game-changers for climate protection.
The debate on sustainable construction has changed significantly in recent years. For a long time, the focus was almost exclusively on a building’s energy consumption during its operational life. Heating energy, insulation standards, and modern heating systems were considered the most important levers for reducing CO₂ emissions. Today, the focus is increasingly shifting to a building’s entire life cycle. As a result, “gray energy”—which was often underestimated in the past—is also gaining importance.
“Grey energy” refers to the total amount of energy already stored in a building. It encompasses the extraction of raw materials, the production of bricks, steel, wood, or concrete, the transportation of materials, and all construction processes leading up to the completion of a building. This energy has already been consumed—it cannot be recovered or reused. If a building is demolished, this invested energy is also irretrievably lost. This is precisely why existing buildings play a key role in climate protection.
Preserve Rather Than Replace—Why Existing Buildings Are So Valuable
Historic buildings are often hastily dismissed as energy-inefficient. In fact, many older buildings do not meet today’s new construction standards. Nevertheless, this view is too narrow. Demolition not only means the loss of valuable architectural heritage but also generates significant amounts of construction waste and releases additional emissions. New building materials must then be produced, transported, and processed. The production of cement, concrete, and steel, in particular, ranks among the world’s largest sources of CO₂ emissions. This is precisely where the insights from historic preservation and climate research come into play. The Association of State Historic Preservation Officers sums up this connection with a clear message: Preserving existing buildings is active climate protection. This is because every renovated building saves the emissions that a completely new building would inevitably cause.
The Federal Environment Agency also points out that climate protection and historic preservation are not mutually exclusive. On the contrary: both aim to use existing resources responsibly and preserve them for the long term. Sustainability does not begin with new construction, but often with the question of whether an existing building needs to be replaced at all.
This viewpoint fundamentally changes the perspective. Instead of evaluating buildings solely based on their heating energy requirements, their overall environmental impact is considered. And this is precisely where many existing buildings perform significantly better than their reputation would suggest.
Historic buildings are part of the solution
Preserving a historic building does more than just safeguard architectural history; it also allows for the continued use of existing resources. Many older buildings are constructed from durable, natural materials such as wood, natural stone, clay, or brick. These building materials have often proven their quality over many decades or even centuries. Unlike the short-lived materials used in modern construction methods, they can often be repaired, supplemented, or reused. Added to this is the exceptional craftsmanship found in many historic buildings. Solid roof trusses, high-quality wooden structures, or traditional masonry often have a lifespan that modern building products rarely match.
This concept, in particular, is gaining increasing importance in the context of the so-called circular economy. Instead of demolishing buildings after just a few decades and replacing them with new ones, the focus is shifting toward long-term preservation. Repairing, restoring, and continuing to build are once again becoming central principles of sustainable construction. This is also changing the role of historic preservation. It not only preserves cultural monuments but also promotes the responsible use of resources. Much of what is discussed today under the term “sustainability” has been part of everyday practice in historic preservation for decades.
Energy efficiency and historic preservation are not mutually exclusive
A common misconception is that historic buildings cannot, in principle, be retrofitted for energy efficiency. However, practice reveals a much more nuanced picture. Not every historic building is suitable for the same measures. Nevertheless, there are numerous ways to save energy without compromising a building’s historic character. Improved roof or floor insulation, window repairs that respect the building’s historic character, modern heating technology, or smart control systems can significantly reduce energy consumption. In doing so, historic preservation does not follow a rigid set of rules but considers each building on a case-by-case basis. The goal is always to find a balanced solution between climate protection, usability, and the preservation of the historic fabric. It is precisely this case-by-case approach that often makes historic buildings successful examples of sustainable renovation. Modern technology is used where it makes sense, while building components worth preserving continue to be utilized. This saves materials, energy, and emissions. The result is a sustainable approach that goes far beyond short-term efficiency gains.
The most sustainable kilowatt-hour is the one already invested
For a long time, the construction industry focused primarily on one goal: building new structures that were as energy-efficient as possible. While this approach is undoubtedly important, it falls short today. This is because a building generates the majority of its CO₂ emissions not during its use, but during its construction. The production of building materials, transportation, the use of machinery on the construction site, and finally the construction itself consume enormous amounts of energy. This is precisely why “gray energy” is becoming increasingly important. It makes it clear that sustainability doesn’t begin with thermal insulation, but rather with the question of whether an existing building needs to be replaced at all.
Every existing building that is preserved conserves raw materials, prevents waste, and reduces the need for new building materials. Especially in times of scarce resources and rising construction costs, this is an aspect that is becoming increasingly important not only from an ecological perspective but also from an economic one. The European Union and the German federal government are therefore increasingly pursuing strategies that place greater emphasis on the existing building stock. The goal is to extend the service life of existing buildings and improve their carbon footprint over their entire life cycle. This brings to the forefront a principle that has always been a given in historic preservation: the most sustainable building is often the one that already exists.
Historic Preservation as a Model for Sustainable Construction
Historic preservation is often equated with conservation. In fact, however, its approach is based on a highly relevant principle of sustainability. For decades, it has followed the principle of “preservation over replacement.” Historical building materials are restored rather than replaced, structures are repaired rather than completely rebuilt, and buildings are carefully adapted to new uses. What once served primarily to protect cultural heritage is now proving to be an effective contribution to climate protection as well. This is by no means about preserving historic buildings unchanged. Rather, the aim is to adapt them in such a way that they also meet future requirements. New heating systems, modern building services, or improved energy efficiency can be part of this process, provided they are compatible with the historic fabric. This is precisely where the particular strength of historic preservation lies. It does not seek standard solutions but rather develops individualized concepts for each building. This nuanced approach is becoming increasingly important in light of the climate crisis. After all, sustainable construction does not mean implementing the same measures everywhere, but rather making intelligent use of existing potential.
Many insights from historic preservation are now also finding their way into general construction practice. Topics such as the culture of renovation, building within the existing stock, the reuse of building materials, and circular construction are among the most important future challenges facing architecture today. Historic buildings are thus no longer viewed as obstacles, but as valuable resources.
A shift in perspective that pays off
The discussion surrounding climate protection is changing the way we view our built environment. While demolition and new construction were often seen as signs of progress in the past, there is a growing recognition that the responsible management of existing buildings is often the more sustainable solution. This does not mean that every old building is automatically a historic landmark or that every renovation can be carried out without difficulty. Nor can every new construction be avoided. Nevertheless, it is becoming increasingly clear that existing buildings possess inestimable value—ecologically, economically, and culturally.
Historic buildings tell stories, shape the character of a place, and convey a sense of identity. At the same time, they store enormous amounts of “gray energy” and thus contribute to climate protection—a contribution that is often not even reflected in energy performance certificates or consumption figures. So, preserving a building means not only preserving architecture but also conserving resources. This is precisely why the debate on sustainable construction should be conducted more comprehensively in the future. Energy efficiency remains an important component, but it is only one part of the overall picture. Only when construction, use, maintenance, and lifespan are considered together does a realistic picture of a building’s actual environmental impact emerge.
The Future Builds on the Existing Stock
Grey energy is one of the most important—yet long underestimated—factors in climate protection within the building sector. It makes it clear that every existing building has an ecological value that cannot simply be replaced. Historic buildings occupy a special place in this context. They combine centuries-old building traditions with the sustainable use of resources and demonstrate that longevity itself is an essential component of climate protection. Preserving them saves CO₂, prevents waste, and reduces the consumption of new raw materials. This is precisely why historic preservation and climate protection are not opposites, but rather pursue the same goal in many areas. Statements from the Federal Environment Agency and the Association of State Historic Preservation Officials impressively underscore this trend. Both point out that the existing building stock will play a central role in achieving climate goals in the future. Energy-efficiency improvements remain important, but must take into account the entire life cycle of a building. In this context, “gray energy” becomes a decisive benchmark for sustainable construction.
Perhaps this is why we need to take a fresh look at our historic buildings. They are not relics of a bygone era, but valuable resources for the future. Those who preserve them are not only safeguarding history and architectural heritage but are also investing in climate and resource protection for future generations. In this sense, the existing building stock is not obsolete—but rather a crucial building block for the sustainable construction of tomorrow.
