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Special dimpled sheet tested in the field

When the Adalbert Stifter School was built in Wiesbaden, a new special dimpled sheet was used that will be presented at the BAU 2011 exhibition. Delta-Floraxx Top combines drainage with water storage and filtration. In particular, the sheet’s outstanding laying properties came to the fore in the building project.

The Adalbert Stifter School in Wiesbaden was built to the passive house standard and fitted with an extensively planted flat roof. The new Delta-Floraxx Top sheet was integrated in the roof as a combined drainage, water-retention and filtration layer. Its multiple function aside, what tipped the scale for the laying team were the technical advantages of the dimpled sheet that permitted it to be laid out particularly quickly and efficiently. A team of three took no more than six hours to cover the entire area of 1,200 square metres, after which the planting substrate could be spread right on top of the sheet. The performance characteristics of this new sheet will also be showcased by Dörken GmbH & Co. KG at the BAU 2011 exhibition in Munich.

Consistently ecological
By joining the climate alliance of European cities, Wiesbaden, the capital of Hessen, undertook to take suitable steps to reduce its CO2 emissions by a considerable margin. One step is to aim for increased energy efficiency in the construction and rehabilitation of municipal buildings. The Adalbert Stifter School, too, was planned and built to standards that come very close to the passive house concept. One decision which shows that ecological thinking was applied consistently was to turn the 1,200 or so square metres of flat roof on top of the new building into an intensively planted roof garden. One reason for this is that green roofs trap fine dust and airborne pollutants, besides sustainably improving the ambient microclimate through their positive impact on the humidity cycle and the oxygen content of the air. Another reason is that the building’s energy efficiency is optimised by the heat-insulation potential of a green roof. Even a very simple configuration produces excellent heat protection in summer. Forming an additional insulation layer, a green roof relieves the burden on air-conditioning and ventilation systems, thus helping to reduce energy costs markedly.

Efficient drainage wanted
To ensure that any water reaching the surface and the waterproofing level through precipitation is drained away safely and the plants on the surface are protected from damage by waterlogging, an efficient protection and drainage layer was needed. The contractor, Immo Herbst Innenraum- und Dachbegrünungs-GmbH of Frankfurt/Main, was the first to employ a new special dimpled sheet for this purpose that will be presented at the BAU 2011 exhibition in Munich. Made by Dörken GmbH & Co. KG of Herdecke, Delta-Floraxx Top was developed specifically as a drainage, water-storage and filtration layer for herbaceous flat roofs. Its special octagonal dimples additionally reinforced by ribs give the material an extreme compressive strength of 200kN/m², enabling it to bear even heavy loads. Thanks to its high drainage capacity, the sheet can easily replace a mineral seepage layer although its weight and covering height are markedly lower. At the same time, the dimples store water, thus helping the greenery to survive periods of drought.

The sheet owes this twin function to the newly-developed shape of its 20-millimetre dimples. Featuring a drainage capacity of c. 10L/s.m, the dimples are capable of storing up to seven litres of water per square meter. Excess water drains away downward through perforations in the sheet, entering the network of drainage channels formed by the dimple structure. Thus, there is no chance of the soil becoming waterlogged, which might harm the plants. The fused-on filtration cloth keeps the drainage channels from silting up.

Laying advantages
What the building contractor’s team was mainly interested in, however, were the technical advantages displayed by the sheet as it was laid out. The fused-on drainage and filtration cloth eliminated the need for an entire operation, so that the planting substrate could be spread on top of the sheet immediately after laying. Moreover, its low weight made the new dimpled sheet easy to handle at work. As usual, the material was laid out swiftly straight from the roll, with the dimples facing downward. Laying performance was additionally enhanced by the 2x10-metre roll size. Sheets were laid out so as to abut one another laterally, with the filtration cloth overhang along one side of the sheet overlapping the neighbouring sheet by about 10 centimetres. This keeps planting substrate from entering the joints and clogging up the drainage system. At the ends, sheets were overlapped and held in place with rivets applied with a Delta-Floraxx riveter, forming an impact-resistant seam. A riveting tool and rivets are included free with every pallet of material. Once the sheets had been laid out, the waterproofing was safe from mechanical injuries and harmful thermal exposure and would bear the weight of a man or a wheelbarrow straight away.

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