Sponge Balcony

The Evangelical Lutheran congregation of Hof-Kreuzkirche faces the challenge of addressing increasingly extreme weather events and becoming climate-resilient. Particularly during prolonged dry spells, the Kreuzkirche—a structure over 60 years old—and its surrounding grounds (which are largely paved or sealed) are exposed to intensifying urban heat island effects. The church’s structural design poses a specific challenge, as it does not readily accommodate the use of standard sponge elements. Furthermore, a planned photovoltaic system for the church roof must be taken into account. Due to its pitch, the roof is unsuitable for a modern green roof installation; this eliminates one of the most effective ways to reduce heat buildup inside the church on hot days. At the same time, modern green roof systems offer significant storage capacity, allowing collected rainwater to be used for irrigating the property, for instance.

To enable the collection of rainwater nonetheless, the Water Infrastructure and Digitalization research group has proposed constructing a special "balcony" around the church roof; this structure captures and stores the water in a strip of green roofing, releasing only a reduced amount into the sewer system during heavy rainfall. The cooling effects of the green strip are intended to boost the electricity yield of the PV modules, while the shrubs within the green roof are arranged specifically to increase evaporation.

Work Package 1: Literature review on the use of gradation systems for evaporation in 'sponge elements'; Work Package 2: Development of design or dimensioning approaches for the gradation/evaporation elements, including an investigation into suitable types of timber; Work Package 3: Preparation of a structural engineering report on the supports and adjacent church walls, WP 4: Development of the 'Sponge Balcony' structural design, WP 5: Adaptation of the Purple Roof System for use in the 'Sponge Balcony', including the addition of gradation/evaporation elements, WP 6: Development of a water balance, WP 7: Design of the technical water management system (sensors, pumps, pipework, control system), Work Package 8: Design of the overall 'Sponge Balcony' concept.