Daia Zwicky, Head of the Institute of Construction and Environmental Technologies (iTEC, HEIA-FR), will present the ConDensUrbEN project. This project aims at developing concrete technical concepts for the densification of urban living areas by raising the height of existing buildings in a cost-effective and ecological manner. Follow the presentation on 12 April 2022 from 11:00 to 12:00 at bluefactory Fribourg (room HBL0 21A). For streaming, link on demand.

All demographic predictions forecast an increased development of urban zones. To avoid urban land spread, as also required by current spatial planning laws, these zones need to be densified towards the interior. Besides using abandoned industrial ground for the construction of condensed residential buildings, one of the most promising approaches is to heighten existing buildings by adding further stories. Demolition and reconstruction of existing buildings is certainly not the way to go, considering the important amounts of waste, energy and new materials necessary to do so.

To maximize the number of additional stories on an existing building, the added construction elements need to be as light as possible to limit structural interventions on the existing structure to a minimum. This can be reached by using lightweight construction materials in usual dimensions or by using heavier but highly performing construction materials in very small dimensions. In addition, the heightening construction needs to satisfy a multitude of further requirements, e.g. thermal and acoustic insulation, and fire protection. Based on a representative case study of existing urban buildings, a multitude of generic materializations for the new construction elements were conceived and dimensioned in the framework of this project, funded by the HES-SO Engineering and Architecture domain and elaborated in collaboration with the institutes TRANSFORM (HEIA-FR), insit and IGT (heig-vd).

Practice-oriented combinations of horizontal and vertical construction elements are evaluated for their ecological and economic impacts, considering different structural, insulating and cladding materials, as well as different story layouts and number of added stories. These results allowed to identify appropriate and inappropriate combinations of materials and elements (“dos and don’ts”) for the considered boundary conditions. They further allow to detect governing construction elements and materials, providing the basis for further ecological optimization tracks. Overall, this study showed that there is no simple answer to the question what is the most appropriate construction mode (e.g. timber or steel).

Constructing the highest possible heightening is principally beneficial in terms of relative ecological and economic impacts but requires tradeoffs in the story layout. Such a maximized heightening is also favorable for the amortization of the energetic refurbishment of the existing building. It was further discovered that there is no correlation between the mass of the added construction and its ecological impact. However, it could be detected that targeting a reduction of the economic impact is normally disadvantageous to the ecological impact while an increase in economic efforts does not necessarily result in a reduced ecological impact (on the contrary). Detailed results from the developments and evaluations performed in the project shall be given in the Smart Living Lunch presentation, ultimately resulting in recommendations of preferable materializations and inappropriate materializations.

Heightening of four floors with restricted story layout: comparison of different construction materializations in terms of relative differences in construction cost and embodied carbon, with reference to a traditional timber frame construction. © Daia Zwicky

The Smart Living Lunches take place once a month from 11 am to 1 pm in Fribourg to present the research activities of the Smart Living Lab. A lunch is served after the presentation. These events are designed for the Smart Living Lab’s community.

SMART LIVING LUNCH | The ConDensUrbEN project: sustainable heightening of existing buildings 11:00-12:00 | HBL0 21A | Bluefactory, Fribourg



Daia Zwicky

​​Institute of Construction and Environmental Technology (iTEC)
Full Professor UAS- HEIA-FR
-construction materials science and technology
-environmental awareness
-load-bearing systems


ConDensUrbEN project