Stefanie Weidner: “We should no longer implement any projects without putting energy and sustainability at the forefront.”

Thomas Geuder
9. February 2023
Dr.-Ing. Stefanie Weidner (Photo: Janine Kyofsky Fotografie)

Thomas Geuder: Mrs. Weidner, planners in the construction industry have long been concerned with environmentally friendly techniques and technologies. Yet, particularly as climate change has increasingly become a focus of public attention, the demand for climate-friendly construction has gained enormous momentum in recent years. As an expert, what is your current view of the energy and sustainability issue?

Stefanie Weidner: Yes, the topic has noticeably gained momentum. That's actually a good thing, because we should no longer implement any projects without putting energy and sustainability at the forefront. However, I personally still too often see a lack of courage, especially on the part of clients and legislators. On the one hand, too few requirements are being imposed too hesitantly. On the other hand, the initial purchase price is still the all-determining factor. Manufacturers can take a stronger lead in this regard by spreading possible additional costs for sustainable products across their entire product range. 

The greening of facades and roofs of the Calwer Passage creates an urban space with a natural, healthy climate. In case of heavy rainfall, the greenery and substrate build-up act as temporary storage for water masses. (Photo: Kilian Bishop)
In addition, the plants are able to reduce local concentrations of particulate matter and counteract the otherwise observed overheating of densely built-up areas in summer (the so-called urban heat island effect). Hence, the local microclimate is significantly improved. (Photo: Kilian Bishop)

One of the many lessons learned from the terrible Ukraine war is that energy, especially in the form of heat and electricity, is much more valuable than many previously assumed. How do you perceive this change in your everyday work?

I notice that the question of the energy source used is now being discussed even more intensively, especially for existing buildings. Up to now, gas heating has been accepted as a transitional technology. The current situation makes it all the more important to push ahead with the transition to an electric heat supply with all our might, to expand district heating networks more quickly and to minimize emissions they produce. Apart from that, the general aim is to save as much energy as possible. We are now seeing a much greater willingness on the part of clients to adjust the limits of specified minimum or maximum temperatures indoors or to give preference to innovative technical solutions.

The research project is the world's first active house. (Photo: Zooey Braun)
Thanks to a sophisticated energy concept and a self-learning building control system, it generates twice as much energy as it consumes itself — and it does so from sustainable sources. (Photo: Zooey Braun)

For many years, the term sustainability has always been used when talking about saving energy and resources — and has often become watered down in the process. At Werner Sobek — a company that positions itself as a “pioneer for a future-proof environment” with core competencies in the fields of engineering, design and sustainability — you are, among other things, Director Sustainability Strategies. What specific strategies are you thinking about?

On the one hand, this involves strategies that affect our internal processes and structures, such as workflows for optimizing resource and emissions consumption or new approaches from research that can be transferred into practice. On the other hand, we advise investors, architects and municipalities at a strategic level (but often with specific project reference) on how to design and manage their portfolios and projects for the benefit of climate protection. In addition to the Triple Zero® concept (zero fossil energy, zero waste and zero emissions), we always focus on the environment with aspects such as biodiversity and microclimate as well as the well-being of the users.

The world's largest adaptive building is located on the university campus in Stuttgart-Vaihingen. It was built as part of the Collaborative Research Center 1244 “Adaptive skins and structures for the built environment of tomorrow”.  (Photo: Uli_Regenscheit)
The goal of the research project is to investigate how buildings can be designed with as few resources as possible while maintaining maximum user comfort through the targeted use of adaptivity. (Photo: Uli_Regenscheit)

With regard to the topics of energy, resources and sustainability, the construction sector is currently at an important turning point. Which ideas and technologies do you consider to be particularly future-oriented?

First of all, the aim is to reduce. And this is true at both the building level and the component and material level. (New) construction volumes can be reduced through efficient floor plans and diversity of use, as well as through the continued use of existing building fabric. This does not necessarily require new technologies, even though digitization of planning is certainly an important aspect. At the component level, technologies such as Gradientenbeton® (gradient concrete) are promising, but so are other approaches to mass reduction in ceiling systems, such as the HiLo system developed at ETH Zurich. At the material level, too, there are numerous approaches to circular equity and CO2 reduction. In addition, there are systemic approaches, such as self-learning building management systems.

Not least important for the implementation of sustainability concepts are the clients, who have to go along with the idea of possibly higher investments for the benefit of environmental and climate protection. Have you recently observed a greater awareness in this respect?

Awareness is definitely increasing, although not to the same extent everywhere. There has been a boost from ESG (Environmental Social Governance) and the ecological criteria of the EU taxonomy. This is because it involves the financing of projects — a truly good lever. I hope that the requirements imposed by legislators on new projects will be further increased so that they actually become a steering tool towards meeting the Paris climate targets. Unfortunately, it still shows that without the necessary compulsion or corresponding incentive, only very few clients voluntarily meet more ambitious targets than are absolutely necessary. 

The Urban Mining & Recycling (UMAR) experimental unit is part of the NEST research building on the campus of the Swiss Federal Laboratories for Materials Science and Technology (Empa) in Dübendorf, Switzerland. (Photo: Zooey Braun)
The design of the UMAR developed by Werner Sobek together with Dirk E. Hebel and Felix Heisel shows how a responsible use of our natural resources can be combined with appealing architecture. (Photo: Zooey Braun)

Because of the enormous increase in costs and because of climate change, the correct use of energy is currently on everyone's lips, but not everyone can be an expert. What everyday advice do you have for sustainable energy use, and how do you practice sustainability yourself?

Recommending such banal advice as wearing thick socks and a warm sweater would fall short of the mark — even if, of course, each and every one of us can contribute to getting closer to climate protection by using our resources sparingly. In the long term, however, there is surely no alternative for all of us but to switch the generation of electricity and heat for our buildings completely and as quickly as possible to emission-free energy sources. 

On a personal level, I currently have to travel a lot for work reasons. At least I try to keep emissions as low as possible through my diet and consumer behavior. And I have refrained from the idea of having to live in a newly built single-family house.

Dr.-Ing. Stefanie Weidner has been office manager of Werner Sobek København since 2022 and Director Sustainability Strategies since 2021. In addition, she is a lecturer at the University of Tübingen and a consultant to the German Sustainable Building Council (DGNB). She studied architecture and urban planning at the University of Stuttgart and architecture at the University of Melbourne. From 2014 - 2021, she was a research associate at the Institute for Lightweight Structures and Conceptual Design (ILEK) at the University of Stuttgart. In 2020, she completed her doctoral studies with distinction (summa cum laude) at the Faculty of Architecture and Urban Planning at the University of Stuttgart.
ISH presents marketable solutions for a sustainable future
ISH, the world's leading trade fair for heating, ventilation, air-conditioning and water, will once again be inviting visitors to Frankfurt am Main from March 13 to 17, 2023. At the leading international event for the sanitary, heating and air-conditioning technology sector, the industry will showcase its marketable products and ideas for achieving climate protection targets in buildings. Around 2,000 companies, 70 percent of them from abroad, are expected to attend. They will present solutions for renewable energy sources, sustainable water use and clean air.
The exhibitors are spread across the two sections of the trade fair, ISH Water and ISH Energy. Modern bathroom design and sustainable technology for the use of water resources are the focus of the ISH Water section. In Halls 1 to 6, visitors will find innovative products and solutions for lifestyle-oriented bathrooms, hygienic drinking water installations, time-saving installation and fastening technologies and software solutions. The range of products and services at ISH Energy in Halls 8 to 12 ranges from innovative heat generation with a focus on sustainable heat pump technology, modern heat distribution and delivery and systems to intelligent home and building automation, through to cooling, air-conditioning and ventilation technology. 
The ISH Contactor offers an up-to-date overview of all exhibitors taking part in the fair at
The exhibitors' products and solutions will be flanked by an extensive accompanying program. Trend forums, competitions, specialist forums, guided tours and lectures provide an opportunity to obtain information, learn more and network. 
Visit for the latest news.
All information about the ISH is available at
Talks + Tours and Guided Tours at ISH 2023 from 13. - 16. March 2023
Tilla Goldberg (Ippolito Fleitz Group), Alexandra Mrzigod (Werner Sobek), Jana Vonofakos (VRAI interior architecture), Julia Schneider (iam interior.architects), Malte Just (Just/Burgeff Architekten), Lien Tran (Lien Tran Interior Design), Michael Burghaus (architekturbüro .pg1), Markus Pfeil (Pfeil & Koch ingenieurgesellschaft)
Talks + Tours and Guided Tours at ISH 2023 – Information and registration

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