Acoustically optimised drainage pipes

Is a reluctance to move away from traditional materials still holding us back when it comes to material selection for key products such as acoustically optimised drainage pipes and fittings? Sophie Weston, Channel Marketing Manager at Geberit, looks at the properties of four key materials used for drainage pipes and fittings and asks what learnings we can gain from the European market.



aced with the challenge of balancing increasingly stringent efficiency targets with ever-squeezed project budgets, it is inevitable that some systems within the building will be repackaged again and again within new project specifications, because they work at the right cost, without impacting efficiency. But what if there is a better solution? What if this inertia is preventing enhanced acoustic performance, preventing installation efficiencies and costs savings from being achieved?

One such example is the soil and waste drainage system – clearly a critical part of any building, and one in which failure could be costly, disruptive and unpleasant for property owners, operators and users. Yet, despite continued innovation and development of materials, many specifiers still stick to the material they used in the last project.

Each material choice comes with its own advantages and disadvantages, but before I explore the merits of four specific materials in more detail, it is important to consider the demands of drainage pipes – and how this will impact specification.

Effective drainage specification

There are the obvious considerations, like acoustic performance, flexibility of installation, lifespan of the pipe and cost, which encompasses both the material cost and installation cost. Pipes can be connected using either mechanical clamps, push fitting, solvent welding, butt welding or electrofusion welding, depending on the specifier’s material of choice.

We must also consider the smoothness of the pipe bore and the hydrophobicity of the inner pipe – how well it repels water and, therefore, avoids blockages. For metallic pipes, we must factor in susceptibility to corrosion, including whether any coatings are required.

Now, let us examine four material options for soil and waste drainage systems in more detail; cast-iron and HDPE (high-density polyethylene), commonly used for higher-value specification projects, then PVC (polyvinyl chloride) and enhanced polypropylene composite, offering a lower-cost alternative.

Cast-iron credentials

Cast-iron is an alloy of iron and carbon that provides intrinsic acoustic properties, as the material is both dense and thick, preventing air transmission. However, cast-iron is more expensive to purchase and install when compared with plastic alternatives.

As an iron-based material, it is susceptible to corrosion; whilst modern cast-iron pipes have more advanced coatings, many older buildings are inevitably facing corrosion issues after 40 or 50 years of service from their original drainage systems.

Most significantly, cast-iron pipes are also more likely to build-up depositions than a plastic pipe due to the roughness of the pipe bore. A new cast-iron would typically offer a roughness value (the relative roughness of a pipe against the size of its diameter) of 0.26mm, compared to 0.0015mm or below for plastic alternatives.

Through decades of constant use, this surface roughness will gradually worsen, and deposits will start to grip to pitting in the pipe bore. Even with regular cleaning and maintenance programmes in place, this can lead to serious blockages and clogging with cast-iron, which will eventually cause leaks if left untreated.

A shift towards HDPE

Offering a viable alternative to cast-iron, HDPE is becoming an increasingly popular material for drainage pipes and fittings in commercial buildings.

HDPE combines the lightweight flexibility and installation benefits of plastic pipes with the robust, durable properties required for commercial applications. Although HDPE is not the lowest-cost material, the initial investment can often be outweighed by reduced maintenance costs and extended system lifecycle – not to mention the peace of mind that comes with a strong and reliable welded solution.

HDPE pipes have a smooth bore which is maintained throughout their lifetime, helping to repel any waste that might attach to the inside, and they are reasonably hydrophobic – the interior of a HDPE pipe can often be cleaned thoroughly simply by flushing the toilet or running the tap.

It is also a chemically-inert material and insensitive to high water temperatures, able to withstand hot water up to 90°C and even boiling water, unlike PVC which has an upper limit of 75°C. This is particularly important in applications such as hospitals due to the nature of waste deposited through the drainage system.

PVC – the old favourite

Unlike cast-iron, PVC does not provide strong acoustic performance, so lagging is often required with extra time and cost implication. PVC is also a relatively brittle material, particularly in cold weather. It is not uncommon with commercial applications for PVC drainage to be installed, only to be damaged later by subsequent contractors. This can add unforeseen project costs.

However, currently around 75% of soil and waste pipes and fittings sold in the UK are made from PVC, which is lightweight, and easy to attach to walls. Like any plastic pipe, it also has a smooth bore, so is less likely to experience clogging from a build-up of deposits in the same way as cast-iron.

Enhanced polypropylene composite

The fourth option is relatively new to the UK market but is the latest demonstration of the UK building products market taking the lead from European product development. Enhanced polypropylene composite is a proven material, used for many years on the continent and now finally delivering benefits to UK specifiers, engineers and installers too.

Geberit Silent-PP is made from mineral reinforced polypropylene, improving the physical properties of the material and achieving first-class acoustics optimisation, effectively reducing the natural vibrations and noise.

Crucially, it is comparative in price to PVC pipes and fittings, which makes it a fantastic choice for acoustically-sensitive applications such as hospitals and hotels. In fact, enhanced polypropylene even has the ability to provide an opportunity to deliver overall project cost savings compared to lagged PVC by reducing or removing the need for lagging on some projects.

Be open to innovation

Ultimately, the choice of material for waste drainage pipes and fittings will come down to a number of considerations, but the key takeaway is to not rule out different or new acoustically optimised materials.

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