Free your build from the water trap

Tim Wootton of Wavin explains how compact alternatives to traditional water traps can provide the practical answers while enhancing design freedom for housebuilders in kitchens and bathrooms.

The needs of modern housing developments can present a range of challenges to plumbers and contractors when it comes to installing pipework to appliances and fittings using traditional water traps.

They face a combined challenge of preventing foul sewer gases entering properties and complying with Part H of the Building Regulations, while also freeing up as much space as possible in tight building footprints. Whether it is providing a pedestal washbasin in an en-suite bathroom, a bath or shower installation, or simply an integrated waste bin under the sink to save space in the kitchen, standard water traps can compromise space, in turn limiting design freedom or leading to possible issues on site.

Being able to install a trap that saves space can provide significant benefits in domestic projects, whether as a result of reducing the size of the trap itself or by enabling it to be installed vertically or horizontally in plumbing systems. This can deliver both time and cost savings thanks to its ability to achieve a simpler system design, which can prove particularly beneficial in large housing developments.

Solving problems on site

There is a range of potential problems on domestic installations with standard waste trap solutions. For example, in order to accommodate the U-bend of a traditional trap, installers may have to cut the floor under a shower. Alternatively, they might consider installing a shallow bath trap – this will fit into the space, but is likely to be in breach of Building Regulations. Fitting a compact valve which can be installed horizontally under a bath avoids this risk.

Traditional water-based traps such as ‘P’, ‘S’ and bottle trap varieties have been used for many decades as a solution to prevent sewer gases. All such products however are vulnerable to failure if water is removed from the trap, which can result from siphonage or evaporation from lack of use.

There are versatile options available which do not rely on water being present to operate fully, such as HepvO from Wavin – an alternative to a traditional waste trap. The self-sealing waste valve comprises a purpose-designed membrane which creates an airtight seal between the living space and the drainage system, avoiding the need for water in the trap. The membrane opens under water pressure of an emptying appliance, after which it closes to form a tight seal.

Design benefits for homeowners

The design flexibility offered when installing a compact waterless trap comes into its own in bathroom layouts; because the trap acts as an air admittance valve, the pipe run to a basin can be extended from 1.7 m to 3 m without needing to increase the pipe size from 32 mm. It also makes it easier to install slimline pedestals, as the compact product can be installed ‘in-line’ vertically, allowing the waste pipe to drop in a straight line from the appliance outlet. In addition, traditional secondary vent pipes or additional branch ventilation may not be required.

Many homeowners wish to maximise storage space under the kitchen sink by installing an integrated waste bin, so a compact waterless trap is ideal for opening up the space. In addition, a greater number of appliances can be connected without risking pressure fluctuations and operation can be silent, even under abnormal pressure.

Compact waterless traps can provide an ideal solution for freeing up space and offering an array of design choices for housebuilders in modern housing developments. They also offer a proven and highly-engineered practical alternative to traditional water-based traps which provide an equivalent service life.

Tim Wootton is manager of technical design at Wavin.