French drain - How it works to drain surface water

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What is a french drain?

A french drain is a drainage system whereby a small trench filled with aggregate allows surface water to drain away from the walls of a property. This drainage system is built at a gradient and common in areas that are prone to flooding and are often used to assist basement waterproofing systems.

How does a french drain work?

A french drain system works by burying a pipe in a deep trench around the outside of the property. Small, crushed stones are then packed around the french drain pipe. Next, the soil that was displaced when digging the trench is pushed back on top of the stones and pipe. During periods of rainfall, the surface water flows into a trench and and runs downwards into a pipe at the bottom of the drain. The water travels through the pipe until it reaches an exit point away from the property. The volume of water that can be transported is determined by several factors such as the size of the french drain as well as the design and position.

This process decreases the amount of water surrounding the basement of the property, resulting in less hydrostatic pressure against the foundation walls and, consequently, greatly reducing the risk of leaks and flooding from cracks.

Generally speaking, it is a sound system, but it is imperative that a French drain is installed in a way that will eliminate clogging. Water that gets into the drain will inevitably carry sediment from the soil and without adequate filter systems the drain will eventually clog and need to be dug up for maintenance.

French Drain

When can I use a french drain?

A french drain is normally most commonly used in areas prone to flooding. However, it is important to note that the purpose of a french drain is to assist existing surface water drains rather than replacing surface water drains. Before installing a french drainage system, it is important to ensure there are no faults with any other surface water drainage systems.

How do you install a french drain?

The Code for Sustainable Homes specifies that french drains in the United Kingdom must be designed by civil engineering consultants or other hydraulic engineer professionals. Local authorities in the UK normally require evidence of professional french drain design to ensure it meets national standards. Failure to meet such standards can result in legal action being taken.

Therefore it is crucial that you always contact a professionally qualified and experienced french drain specialist. Incorrect installation could lead to water damage and any damage caused by incorrect installation to your own or neighbouring land would not be covered by an insurance policy.

Speak to a french drain specialist

If you would like to speak to a french drain specialist or have a query regarding structural waterproofing,then contact WIse Basement Systems on 0808 301 4120 or click to contact your local branch.

Alternatively fill out this short contact form to get in touch with one of our waterproofing specialists.