“Ms. Lemaitre, you head the German Sustainable Building Council. What should one keep in mind when renovating or building a house?
As a first step, everyone should consider what they want and how much space they actually need. What will your living situation look like in the future? Do you have children, or do you plan to have them? And what happens once the children move out? Early on, a builder can think about the floor plan—for instance, whether it might be possible to create two separate living units later, allowing one to be rented out. Furthermore, summers are becoming increasingly hot. Large, south-facing glass facades no longer make sense. Air conditioning should only be installed where it is truly necessary. One might also ask: How can the space be effectively ventilated? Few people would leave floor-to-ceiling windows on the ground floor open at night. Ceiling fans, especially in bedrooms, are a great way to prevent overheating.
Are renewable raw materials like wood important as building materials, or is concrete still an acceptable choice?
All materials are legitimate. However, one should always choose the material that is appropriate and durable for the specific intended use. In residential spaces, wood is a wonderful material. For materials that start as liquids and later harden, it is crucial to ensure they are free of harmful substances. Some coatings off-gas significant amounts of chemicals, which is unhealthy and increases the risk of allergies.
Buying, building, or renovating a house are major undertakings—and they are expensive regardless. Do some people forgo sustainability to save on costs?
If you plan a building first and only then try to incorporate sustainability, costs will inevitably rise. It is far better to look for synergies from the very beginning. You can decide early on: I want healthy building materials; I will build only as much space as I actually need; and I will prioritize adaptability for future use and long-term durability.
What role does energy supply play?
It is a crucial factor. Many people would like to have an energy-self-sufficient building—though that is a difficult goal to achieve. In the residential sector, it is possible to generate and consume one’s own energy using a photovoltaic system. This offers financial benefits and reduces the owner’s dependence on volatile energy prices. Those who plan ahead and view sustainability as an integral component can avoid additional costs.
The "traffic light" coalition government sought to promote the use of heat pumps through the Building Energy Act. Now, the coalition—comprising the Union and the SPD—intends to transform this into a "Building Modernization Act." Does this represent a step backward for climate protection?
Yes, unfortunately! The supposed "freedoms" introduced actually create uncertainty, particularly for private property owners. What might appear to be a cheaper investment today actually poses a significant financial risk in the coming years—and is, at the same time, detrimental to climate protection. The planned "bio-pathway" (a gradual transition strategy) will, in particular, cause gas costs to soar; furthermore, the price of fossil gas will rise due to increasing CO2 levies. In short, there are two factors driving up costs—both of which directly impact private households.
Is the demand for sustainability declining?
I have mixed feelings on this. In recent years, many "hobby activists" have championed sustainability—the more radical their approach, the more attention they garnered. Yet, in reality, many buildings continued to be constructed just as they always have been. Due to political hesitation and various other global crises, some people now believe they no longer need to concern themselves with climate protection. Those who were never truly convinced in the first place are using this current "headwind" as an excuse to stop engaging with the issue altogether. Within the real estate sector, some no longer consider sustainability to be important. Fortunately, however, many others are continuing to pursue this path.
How significant is the condition of a building when it comes to securing a loan?
Banks must mitigate their own risks, and they generally prefer to finance sustainable buildings. An investor recently mentioned that he was unable to obtain financing from his bank even though the building was in top condition. However, they were unable to provide any information regarding its ecological quality. Later, they had to explain more to the bank about the building’s future and sustainability. After all, a vast amount of wealth is tied up in real estate. If we don’t take proper care of our buildings, it becomes a massive engine for destroying value. Maintaining the value of a house doesn’t happen for free—otherwise, you might find that no insurance company is willing to cover it anymore.
At what point will an insurance company refuse to cover a building?
Insurers look closely at the condition of a building. Is the owner taking care of it? What is stored in the basement? How high is the probability of damage occurring? If you build in a flood-prone area—or already own a house there—it might be necessary, for instance, to raise the threshold at the entrance to the basement stairs by half a meter.
What is the value of sustainable construction?
In principle, the goal is to construct and operate a building with minimal CO2 emissions and no pollutants. However, conflicts inevitably arise in the process. Sustainability is about navigating and resolving these competing objectives. Our guiding principle is this: a building that people enjoy using is one that will endure and be well-maintained. To achieve this, a structure must prevent overheating in the summer and offer protection against extreme weather, such as heavy rainfall. In flood-prone areas, for instance, it is best to keep technical equipment out of the basement.
When it comes to building materials, some favor renewable resources like timber, while others focus on reducing the carbon footprint of concrete. Which approach is more effective?
The objective is to minimize the carbon footprint of the materials used. Even renewable raw materials must be transported to the construction site, which generates CO2—so logistics matter. A sound approach is to consider which materials can be omitted entirely. Do I really need to install carpeting? Or could I use a wooden floor that can be sanded down and last for 50 years? Every square meter that isn’t built represents the best possible saving. The same applies to building systems and technology.
But aren’t these systems supposed to save energy?
Building systems and technology represent the cost category with the sharpest price increases. Unfortunately, these systems often fail to perform as predicted. New buildings frequently consume about 30 percent more energy than their theoretical projections—often because the systems were never properly commissioned, are poorly maintained, or are incorrectly configured. When something breaks, no one takes responsibility. Managing a modern building requires IT specialists to ensure that all the sensors function correctly.
So, you would prefer to do away with complex technical systems?
It is better to have less technology—relying instead on natural ventilation and external sun-shading solutions. Air conditioning should only be used where it is truly necessary. In care facilities, for instance, cooling is often entirely absent. In hospitals, operating rooms are air-conditioned, but other areas rarely are. During a heatwave, hospitals must carefully consider which patients to relocate to cooler spaces—a stark contrast to the cooling we provide for premium properties in Frankfurt. Some might think: "If all our electricity comes from renewable sources, why not just run the air conditioning?" But that same electricity could be put to better use elsewhere.
If a property owner has installed a heat pump and a photovoltaic system, is it still necessary to insulate the building, or can that step be skipped?
No, it shouldn't be skipped—though it is a matter of finding the right balance. The key is to move away from implementing measures in isolation, without considering the broader context. Whether it’s insulating the roof or basement, replacing windows, or upgrading the heating system, a full-scale renovation isn't always required immediately. It is more effective to proceed step by step, gradually reducing energy consumption—which, in turn, lowers utility costs. Studies show that even installing a heat pump in an unrenovated building makes a difference. Often, it makes sense to start by replacing the windows in the living room; residents spend a lot of time there, and it is typically the room that requires the most heating. But it doesn't have to be an "all-or-nothing" approach. In fact, when homeowners opt for a complete, all-at-once renovation, they are often surprised to find that their energy consumption doesn't drop as much as the theoretical calculations predicted.
What is the best approach for a property owner looking to renovate their building?
You need a renovation roadmap. Unfortunately, we have lost the culture of caring for our buildings and maintaining them on a regular basis. It helps to take a fresh look at the property from time to time: what needs to be renewed? And when a component breaks or is due for replacement, what quality of replacement should be installed? This means that renovation costs no longer represent a daunting, monolithic sum; instead, maintenance can be planned over time. My advice to anyone who owns a building is this: take a serious look at its current condition! Work with an energy consultant or an architect to create a plan. This should also address the question: what should I do if something breaks? If that happens, you’ll be prepared and able to quickly install a better component or piece of equipment.
What can a property owner do themselves?
The best approach is to regularly review energy consumption and utility bills. Anyone can also consider whether they still need old electrical appliances and how they might improve ventilation.
The initial investment for a new heating system or new windows is often high, yet the savings only become apparent later on. How can this gap be bridged?
By being honest about the reality: it simply takes time for such investments to pay off. In the past, people would install gas or oil-fired heating systems in new homes without considering how energy prices might evolve. The primary goal was simply: "I don’t want to be cold in the winter." The situation in Ukraine introduced a great deal of uncertainty: How much will prices rise? Will there be enough natural gas available? Will we be cold this winter? That came as a shock to people. Having an alternative to natural gas offers greater security.
In closing: What tip can help save money during a renovation?
It is important to compare different tradespeople. When you receive a cost estimate, you might well be taken aback—often because you lack the context to evaluate it. In such cases, it is wise to compare options and ask questions. No one should simply accept the first offer they receive.” [1]
1. "Klimaanlagen nur da, wo sie notwendig sind": Christine Lemaitre führt die Deutsche Gesellschaft für Nachhaltiges Bauen. Ein Gespräch über Baumaterialien, Gebäudetechnik und den Sinn teurer Sanierungen. Frankfurter Allgemeine Zeitung; Frankfurt. 24 July 2026: 20. Von Jan Hauser
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