This is where the HydroSpacer® HS 170 in the Zinco system build-up “Sponge City Roof” comes into play. It provides up to 160 l of storage space per square metre of roof area and subsequently supplies the stored water to the vegetation. The system absorbs up to 11 l/m² of water by capillary action which is then available for the plant roots in the substrate layer. The water moves entirely by itself – without the use of a pump or electrical controls or operating power.

This product innovation was also deserved winner of the GaLaBau Innovation Medal 2026.

From retention to water balance

Zinco has been developing efficient system solutions for the retention and evaporation of stormwater on roofs for about ten years now. The HydroSpacer® is the next logical step: Not only retaining stormwater and releasing it at a delay but purposely returning it to the natural cycle. Large storage capacity in itself does not make a Sponge City Roof. It is only when the water reaches the vegetation in sufficient quantities that it can evaporate over plants and substrate, contribute to cooling and support the local water balance.

It is precisely this perspective that puts the focus on the water balance as per Leaflet DWA-M 102-4/BWK-M 3-4 of the German Association for Water, Wastewater and Waste (DWA): It is not solely the run-off, but the combination of evaporation, infiltration and run-off, which is intended to approximate the natural water balance. For this reason, roofs become a core component in the green-blue infrastructure, particularly in high-density urban areas where there are no evaporation spaces.

Capillarity in context

Zinco goes beyond merely describing the capillary effect and actually makes the capillary action easy to understand.  For a practical application, after all, it is not only relevant that water can rise. The decisive factor is which quantities will be transported over which difference in altitude and within which time frame. The specified value of up to 11 l/m² in 24 hours was established using a vertical level difference of 80 mm between water level and upper edge of the capillary system present at the start of the measurement. During the test, the water level continues to decrease – the actual distance that has to be covered therefore increases over the period of 24 hours.

“Capillarity is only a true performance factor if we know the amount of water that actually has to be transported up over the relevant height and in which time frame”, said Ralf Walker, Zinco Technical Director. “The HydroSpacer® allows us to provide a useful resource for vegetation and evaporation from the stored water – passively, without pumps and without operating power”.

Two storage functions in one system

The system build-up “Sponge City Roof” is intended for use on flat roofs that are professionally waterproofed. The 600 × 600 mm and 170 mm high elements in the HydroSpacer® HS 170 have a cavity proportion of approx. 95 per cent. The storage space can be divided into a longer-term accumulation of water available to the plants in the lower area and an additional temporary retention area. Excess stormwater is drained off in a regulated and time-controlled manner via the retention run-off limiter. In this way, the HydroSpacer® elements carry out the tasks of ensuring water reserves, being prepared for heavy rainfall and providing a load-bearing sub-construction.

Transported vertically, distributed horizontally – entirely without the use of a pump

The components Capistrips® and Capifleece® CF 200 are the technical centrepiece of the system. Four Capistrips® per HydroSpacer® are drawn into the lower storage space. These durable, rot-resistant fleece strips absorb the water and transport it upwards to the top of the element. At the top, the fully fitted Capifleece® CF 200 then distributes the water horizontally and is the contact with the overlying substrate layer. With that, vertical transport and horizontal distribution combine to create a synchronised system – driven solely by the power of capillary action.
The subsequent passive supply of water follows the natural gradient of the available water. If the water level is high, a lot of water is available. Once the level sinks, the feed rate decreases gradually. The important thing is that the HydroSpacer® can still provide the vegetation with sufficient water, even if the water level difference is considerable. If the water storage element is completely empty after an unusually long dry period, it can be refilled, depending on the requirements of vegetation and evaporation.

More evaporation, more space for vegetation

A more prolonged supply of water will keep the vegetation healthy for longer and will extend the phase during which water evaporates, and evaporation cooling occurs. At the same time, more species will have the opportunity to go through their development cycle from growth and blossoming to seed-ripening. This may improve the conditions for permanent, diverse plant communities. The vegetation concepts specifically developed here are nonetheless still within the area of extensive green roofs.

The next step in the development of green roofs

The system build-up “Sponge City Roof” with HydroSpacer® HS 170 ensures that the water retention concept is so much more than just an interim water storage option: It retains stormwater, supplies it to the plants over considerable vertical distances and in doing so it supports the return of the water to the local water cycle – without additional water transportation technology. Zinco therefore brings together stormwater management, plant care and urban climate to create an holistic and efficient solution.

GaLaBau Innovation Medal

The German Federal Association of Horticulture, Landscaping and Sports Facilities (BGL e.V.) has awarded the GaLaBau Innovation Medal once again at the GaLaBau exhibition. This year the spotlight was on sustainable, climate-friendly ideas. Zinco is the proud winner of the GaLaBau Innovation Medal 2026 for their innovative HydroSpacer®.