When it comes to implemenng below ground drainage systems, there is a crucial decision to be made: plasc or clay? Here, Marn Lambley, head of product management at Wavin, explores the benefits of both materials and how they can help to achieve key funconal and environmental objecves.

2020, contractors and engineers across the country now have much more freedom when it comes to specifying below ground drainage systems. While the decision to adopt a specific system used to fall to the water and sewerage company (WaSC) for a specific region – and depend on its preferences regarding jetting pressure and materials used, for example – now all water companies nationwide are working from the same guidelines. Unifying the process in this way is opening up the whole country to new techniques and products, allowing drainage systems to develop alongside other technological advances in the built environment.


However, there still remains one fundamental question over whether to specify a plastic or clay solution. Both are valid options, but there are lots of different factors that come into play – from ease of installation to sustainability, to compatibility with ground conditions. Which you choose depends on the specific requirements of the project, while also often coming down to the individual preference of contractors or specifiers. So, what are the benefits of each?


Plastic and Clay Drainage: Weighing up the Options

ollowing the

introduction of the new Design and

Construction Guidance for foul and surface water sewers in April

Plastic fantastic

Plastic is a highly popular drainage material due to its durable yet flexible nature. Being lightweight, it’s also quick to install and easy to handle, which is a huge benefit for installers working on site and helps to improve project efficiency. Plastic pipes can also help achieve sustainability goals, not only because of their extremely long life span – with our below ground plastic pipes having a BBA-certified life span of 60 years – but also because they can be made from recycled materials. For example, some of our systems at Wavin, including our triple layer OsmaDrain pipe, are made using unique Recycore Technology. What this means is the core of the pipe is made up of high-quality recycled materials – such as double-glazing window frames and other waste products from the housing industry. This improved recycled, microcellular core is sandwiched between virgin plastic outer and inner layers, meaning overall 50 per cent of the pipe is made from recycled materials, helping developers increase their sustainability credentials in a build.

One example of a drainage system that can stand up to its traditional counterparts is Osma UltraRib. The UK’s only single walled ribbed system, it has a unique ribbed design that offers supreme axial rigidity and radial strength, while its unique joint design makes installation quick and delivers optimum hydraulic flow. With a stiffness class of SN8 being able to withstand a jet pressure of up to 2,600 psi, the system has been approved by water companies for sewer adoption and meets the requirements of the new Design and Construction Guidance.

Strength in spades: A case for clay

Clay is a traditional drainage material and over the years has consistently proved to be one of the most effective due to its strength, versatility and sustainability. Clay pipes can bring a multitude of benefits to a drainage system. The material is remarkably reliable and durable, with an average lifespan of more than 100 years. With an inert nature, clay piping is fully resistant to almost all chemicals and


compounds that may be found in the ground. This can make it a suitable choice of material if the drainage project is located on a brownfield site, where residual chemicals and contamination from previous industrial or military use is likely. In these circumstances, by using clay contractors and engineers will have the reassurance of a trouble-free performance and a system that can handle a variety of different conditions.

Due to their strength, clay pipes are also able to withstand a jetting pressure of 7,500psi, allowing blockages to be cleared with reduced risk and in less time, and giving contractors and developers reassurance that they’re investing in a high-performing material. Additionally, when it comes to the bedding process, clay pipes supply 90 per cent of the strength required for the total design load. This means less aggregate is needed as a bedding material and that recycled aggregate can be used. What’s more, clay piping can be highly eco-friendly in terms of its manufacturing processes. For example, with Wavin’s Hepworth Clay products, the material is locally sourced so that environmental impact through transportation and

logistics is limited. Additionally, clay is made using recycled rainwater and even fired using reclaimed heat, which is another important step when it comes to achieving sustainability targets.

Making decisions early doors

A key requirement of the new Design and Construction Guidance states that layouts of developments, including drainage systems, must be considered at the earliest stages of the design process. This is because the products and systems that are selected for a drainage scheme can have a significant impact when it comes to costs, length of a project and, of course, performance. With both clay systems and plastic ones like UltraRib approved for use under the new guidance, it’s important that contractors and engineers consider the benefits of each so they can confidently make an informed decision and select the material most suitable for their project in line with their key requirements, type of land and environmental objectives.

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