Originally the architects were intending to provide the housing towers with masonry infill walls within a reinforced concrete framework – a conventional means of construction oriented to the existing red brick buildings. However , the energy-efficiency concept for the student housing towers had to fulfil stringent requirements , with the result that the planners examined whether a wooden structure made up of cross-laminated timber (CLT) would satisfy these demands. In static terms the relatively short spans in the towers and their y-shaped cross-section proved suitable for use of CLT. At the same time the massive wooden elements act as planar structural members , enabling them to withstand horizontal forces such as wind load , storey for storey. The architects also varied the geometry of the connections between the timber elements according to storey and load stress.
The nine-storey towers are all 28 meters high and feature ground floors and basements built in reinforced in-situ concrete. Pre-fabricated CLT elements form the supporting structure of the higher floors , and the same material has been used for the elevator shafts and staircases. Both outer and inner walls act as load-bearing elements , with the visible wooden surface of the latter determining the character of the interiors. Fire protection tests at a 1:1 scale helped derive reliable data on fire behaviour , necessary element dimensioning , burning rate and sprinkler capacity. Plasterboard panels incorporated into the individual ceilings and walls and also the screed and insulating material help fulfil fire safety and sound insulation requirements. A number of the load-bearing walls , such as the inner staircase shafts , have a transparent fire-proof coating.
The facades of the residential towers are clad in overlapping pinewood panels , which have been provided a coating based on organic substances to increase their durability but otherwise left untreated. The outer skin on the ground floor level has been additionally provided fire-retardant coating.
The housing towers were built according to the ultra-low-energy house standard , with use of cross-laminated timber reducing CO2 consumption by some 75 percent in comparison to conventional construction means. The buildings are heated and cooled with geothermal energy.