Dr. Kirsten David, a researcher at HafenCity University (HCU) Hamburg, has developed an innovative method for determining rent increases after energy efficiency measures: By means of functional cost splitting, rent increases become appropriate and comprehensible. The planning of the energetic measures is also ecologically optimized. For her dissertation entitled "Functional Cost Splitting for the Determination of Rent Increases after Energy Efficiency Measures", the scientist today receives the "BUND Research Award 2020". With the research award, the Bund für Umwelt- und Naturschutz (BUND) honors scientific work on sustainable development.
Rent increases due to energy-efficient building modernisation are legally permissible and politically desired as an investment incentive. After all, according to the German Energy Agency (dena), around 35% of Germany's total energy consumption is attributable to the building sector. An increase in the renovation rate is therefore necessary from a climate policy perspective.
However, while the legislators assume that such measures can be implemented economically and without affecting the rent, the experience of many tenants is different: Often the rent increases exceed the saved heating and energy costs many times over. In extreme cases, tenants can no longer afford their apartments. "To this day, energy-efficient building refurbishment has a reputation as a gentrification tool," says David. With the method she developed to determine appropriate rent increases, the 45-year-old scientist also wants to contribute to an increased social acceptance of corresponding measures.
"The basis of the politically expected increase amounts is the so-called coupling principle," explains the architect. "Like the Energy Saving Ordinance, it assumes that energy efficiency measures will always be implemented when a comprehensive refurbishment is due anyway. The sticking point: only the modernization costs entitle landlords* to rent increases, but not the costs for the renovation. The latter must be deducted from the total investment sum as "anyway costs". Eight percent of the remaining costs can be passed on to the tenants as a modernisation charge.
"The current regulation is insufficient. In practice, there are manifold demarcation problems between modernisation costs relevant to rent increases and maintenance costs not relevant to rent increases," says David. The method she developed, on the other hand, focuses on the climate-relevant improvement of each individual building component compared to its condition before the construction measure. "Functional cost splitting thus corresponds to the actual basic idea of the legislators, is practicable and enables an appropriate and comprehensible allocation to modernisation or refurbishment costs," says David.
According to the scientist, her approach leads to the omission of measures that are nonsensical from a structural engineering point of view and do not bring about any climate-relevant improvement of the building components: "With my method, such measures are not relevant for rent increases and are therefore uneconomical for landlords. In addition, your calculation method ensures that the modernization levy actually approaches the level of the ancillary cost savings as a rule. The award winner is therefore particularly pleased that the sustainability aspect of her work has been recognised with the BUND Research Award: "Rental housing stock can only be developed sustainably if ecological, economic and social aspects are given equal consideration. Functional cost splitting makes a significant contribution to this."
This year, the BUND Research Award will be presented at a virtual conference. Among other things, keynote speaker and environmental scientist Ernst Ulrich von Weizsäcker will discuss with the three award winners how science can develop more relevance and effectiveness for sustainability goals. The transfer into practice is also an important concern for David. Her next goal is to further develop functional cost splitting into an instrument that can also be understood by laypersons - preferably as an online tool.
Kirsten David is a guest researcher at HCU in the subject areas "Design and Analysis of Structures" with Prof. Dr.-Ing. Annette Bögle and "Construction Economics" with Prof. Dipl.-Ing. Reinhold Johrendt as well as a lecturer in the interdisciplinary study programmes. Her doctoral thesis was supervised by Prof. Dipl.-Ing. Reinhold Johrendt and Prof. Dr.-Ing. Thomas Krüger, (subject area "Project Management and Project Development in Urban Planning") and is freely available:
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