SPACE4free - Retrofitting souterrain areas in 19th century townhouses to apartments with high quality of life and low energy consumption

Planning of durable and damage-free apartments with high quality of life and low energy consumption in moisture exposed souterrain areas of 19th century townhouses. Using innovative ventilation control systems comfortable room climate will be created. Additionally the tolerance of different types of use is ensured. A planning tool enables the scaling of the findings and thus the applicability to various planning situations.

Short Description



Motivation and research question

The title of the research project "space4free" arose from the idea of converting unused basement areas in Vienna's historic building stock into living space and thus allowing urban densification. In accordance with the paradigm of increasing energy efficiency, this should be possible without an increase in heating energy of the existing building, if the consumption of the newly created apartments is approximately equal to or less than the original heat losses through the unconditioned basement areas. Therefore, the primary research question is: Do the heat losses to the basement in an unrenovated building exceed the actual heating requirement of a refurbished basement / garden apartment?

Initial situation/status quo

Gassner & Partner Baumanagement GmbH has been renovating and revitalizing desolate houses, that were constructed during the "Gründerzeit" (late 19th and early 20th century), into modern buildings combining the historical flair with the highest standard of living for around 20 years. Contemporary architecture meets Wilhelminian style elements, while state-of-the-art building technology guarantees modern energy efficiency and innovative renovation methods guarantee a low risk of damage. In addition to attic extension, the conversion of unused basement areas into apartments with a high quality of life makes a significant contribution to urban densification. Highly efficient sub street level / garden apartments are being built in the city, which are resilient against summer overheating, and with their courtyard-facing terraces and balconies, help avoid urban heat-islands.

From a building physics point of view, there are some unsolved questions in the renovation planning of unused basement areas, most notably concerning the problem of moisture and individual user behaviour. A calculation or simulation has not yet been possible. The normative specifications are often not feasible for underground building components and limit usability. Often, basement areas remain musty and unused due to wall dampness, salt efflorescence and insufficient ventilation.
Existing strategies for basement level ventilation are not fit to be applied to apartment usage due to a lack in hygiene requirements.

Project contents and objectives

Based on the two primary research questions, the aim was to limit the energy requirements of the refurbished sub street level / garden apartments to the value of the heat losses to the originally unused basement. In addition, an intelligent ventilation algorithm should be developed, that ensures both humidity-dependent control and user-specific regulation with regard to presence, hygiene and comfort. The moisture loads were determined from existing studies and real room climate measurements. Missing data or boundary conditions were supplemented by plausible assumptions and literature sources. The intelligent ventilation algorithm was subjected to a "proof of concept" by means of component simulations. Furthermore, long-term indoor climate measurements were carried out, which will be continued after the end of the project as part of ongoing quality assurance. An essential part of the project is the assessment of the risk of damage to building components with ground-contact. This was examined in the course of masonry examinations and long-term component monitoring.

Methodical procedure

The project results were mainly achieved through measurements and component tests and / or hygrothermal simulations. At the beginning of the project, material tests were carried out in the laboratory. This generated essential input parameters for the hygrothermal component simulations. In the second half of the project, the effectiveness of certain ventilation strategies was investigated by means of simulation, taking into account the determined material parameters and the assumed boundary conditions. In addition, several room climate monitors provided data on the actual usage of the apartments. The simulation results were partially compared with the monitoring data to allow conclusions about the quality of the simulation results and the functionality of the actual ventilation controls. The energy requirements of refurbished basement apartments were collected from actual consumption data in four selected buildings by Gassner & Partner. This data was compared with simulation results of an unused and naturally ventilated cellar.

Results and conclusions

The range of measured heat consumption of four renovated basement / garden apartments from Gassner & Partner is almost the same as the range of simulated heat losses through the basement ceiling of an unrenovated existing building. This result confirms the research hypothesis that additional living space can be created in unused basement areas without increasing the heating requirements of the existing building. The hygrothermal simulations, taking into account the intelligent ventilation control, show that user behaviour is usually the decisive factor for the moisture balance. At the same time, it turns out that the emissions from the components can be plausibly measured, but only the order of magnitude can be reproduced by hygrothermal simulation. The material models, especially with regard to liquid water conduction and moisture buffering, as well as the three-dimensional modelling of spatial geometries require further research.
Both the data of the indoor climate measurements and the results of the simulations show, that the indoor climate in the basement / garden apartments can correspond to a typical apartment use. In two of the eight apartments examined in long-term monitoring, however, an increased risk of mould formation was found due to high humidity of the room air. The results of selected component measurements in the floor structure of basement / garden apartments show an increased risk of damage only in the floor-wall connection area. Under special conditions, the activation of the underfloor heating is necessary during the transition period in spring.


The monitoring measures will be continued after the end of the project in order to be able to record the long-term effects of certain measures. Publication of the results of this monitoring in scientific journals and congresses is planned.

The intelligent ventilation control that has been developed will be further revised. While in the first version the control is based on threshold values, ramps and moving average values as well as switching hystereses are to be implemented in the algorithm in a revision. Furthermore, a distant goal could be the inclusion of weather forecasts.

In order to make the knowledge gained more understandable for planners, a planning guide for basement / garden apartments with reference to all boundary conditions and the calculation parameters could be helpful. A practical and powerful simulation tool could also be relevant for planning.

Project Partners

Project management

Technische Universität Wien, Institute for Building Construction and Technology, Research Centre of Building Physics and Sound Protection

Project or cooperation partners

Gassner & Partner Baumanagement GmbH

Contact Address

Technische Universität Wien
Institut für Werkstofftechnologie, Bauphysik und Bauökologie, Forschungsbereich Bauphysik
Tel.: +43 (1) 58801 – 207201