Roofing
Optigreen’s clever green roof solution
As one of the UK’s leading suppliers of roof greening solutions,
Optigreen were approached to provide a solution to a challenging water
management problem
THE PROBLEM
When the waterproofing to part of the roof of the Victoria Shopping Centre in Nottingham, originally constructed in the early 1970’s, had begun to fail and required replacement, an additional issue was discovered as part of the refurbishment work. Part of the original roof design, intended to provide a visual amenity for residents of adjacent flats who could access the area, was the provision of large integral brick planters built off the original asphalt waterproofing and filled with shrubs and small trees. Over the years they had become overgrown and presented maintenance issues for Nottingham City Homes who were responsible for the upkeep of the roof areas.
The planters themselves needed to be removed to allow the new waterproofing system to be installed over the entire roof area and a decision was originally taken not to replace them. However, when calculations were carried out to determine the effect of increased rainwater run-off from the roofs if the planters were omitted, it was discovered that the existing drainage system for the building could be overwhelmed during a heavy rainfall event with potential flooding issues. The planters were providing a vital water attenuation facility and helping to delay water discharge from the roof areas.
THE SOLUTION
The project consultants, Bickerdike Allen Partners, approached Optigreen to help develop a solution to the problem with a brief to provide an economic, low maintenance green roof solution that could give a high level of water attenuation.
Green roofs in general provide excellent water attenuation properties as they store rainwater, reduce water run off and delay discharge into the surface water drainage system. A typical extensive sedum roof will
retain around 50% of the rainfall it receives. In this instance, however, calculations showed that a higher level of rainfall discharge delay was needed.
Based on extensive work by their research and development team, Optigreen have been able to optimise the positive effects of a green roof in terms of water management. The result of this is a clever and patented solution for water retention on green roofs using an innovative drainage board system called Meander.
Available in 30 and 60mm depths, the principle behind this system is as simple as it is effective - water flows along a winding route from one chamber to another, just like a naturally meandering river or stream. During heavy rainfall the chambers of the board are filled with water and the water passes from one chamber to the next causing an extended delay in the discharge of excess water, the rate, to some extent, depending on the gradient of the roof. As an example, during a peak rainfall event, with a roof gradient of 2%, and a 60mm depth of substrate, up to 99% of the rainfall can be retained using a Meander 30 board.
In the case of the Victoria Centre, Optigreen proposed the creation of a series of shallow depth green roofs over the footprint areas of the old planters using their Meander Board 30 solution. Once re-waterproofed with a root resistant liquid system, the areas involved were each edged with recycled railway sleepers. They then received a layer of Optigreen’s RMS 300 protection mat followed by their Meander Board, a filter mat, a layer of extensive substrate and a pre-cultivated sedum vegetation mat. This work was carried out by Optigreen’s approved contractor, NRA Roofing Services Limited.
The green roof areas will not only provide an attractive visual amenity for the residents in the adjacent properties but will also provide a vital water management asset for the shopping centre for years to come.
OPTIGREEN
TEL: 0203 589 9400 43
WWW.OPTIGREEN.CO.UK
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