pro landscaper magazine
pro landscaper magazine

ACO Presents: Building Threshold Drainage Series

by | 12 Jan 23 | Promotion

When creating or refurbishing a garden, patio, or other landscape, the importance of effective drainage must not be forgotten. Part three of this four-part series sees Rob Butcher, Design Service Manager at ACO Water Management examine the key considerations landscapers need to incorporate into their plans when installing threshold drainage.

An essential component of any home is the combination of outdoor and indoor spaces, and the current trends in house design clearly highlight this. The concept of having a step-free, level traverse from their inner space onto the patio is one that more and more homeowners are embracing. Due to this, threshold drainage has to be designed and installed correctly in order to prevent unwanted and frequently hazardous water ponding. There are a number of factors to take into account, with drainage channels being one of the most important aspects.

The Bare Necessities of Drainage Channels

To design a successful threshold drainage system, threshold interceptor drains are vital. These solutions prevent flooding from the external area spreading into the dwelling, while at the same time, do not compromise the aesthetic.

This is especially pertinent with bifold doors and level threshold access applications. Typically, these doors are designed with a running track at the bottom that leaves a slot for rainwater to collect in when the doors are closed. In these situations, a correctly specified channel, such as ACO Water Management’s AS350 Channel Drain, should therefore be installed in front of the running track to percolate the water out to a suitable outlet.

The AS350 allows for the waterproof membrane to be clipped into it to accept water from the bottom track outlets when using bi-fold doors. Once the lid of the channel is added and the membrane is fixed in place, it means water running down the door and into the bottom track is caught in the drainage channel. The lid of the channel goes up to the finished floor level which can then be completed with desired effect, such as paving slabs or decking.

Best practices with drainage channels

Threshold channel drain gratings must be flush with the bi-fold or patio doors and installed correctly to prevent splash, ponding or damp problems. Also, selecting high quality products should be a priority to avoid leakage, breakage and potential trip hazards caused by the drain itself.

Disposal of the rainwater is just as important, and this facet cannot be forgotten when installing drainage channels. ‘Phantom drainage’ is a prevalent malpractice across threshold drainage, whereby the linear channels are connected to nothing. Without a suitable outlet there is nowhere for the water to drain and it will continue to collect until the channel overflows. This is why landscapers must always determine where the collected surface water will be disposed of when implementing threshold channel drains.

This is the third instalment of ACO’s Building Threshold Drainage Series. In part one, we talked about the damp proof course, while in the second part, we looked at gradients and how to remedy waterlogged gardens.

For more information on threshold drainage and the solutions available, visit

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