How do I install a French drain?

A French drain involves digging a trench for discrete and effective drainage of surface water and flood plains. French drains can be very small or very big, dependent on the amount of water that needs draining and the size of the area where the flooding or surface water will be. It sounds like a big job but the list of tools for installing a French drain is short.

What you need to install a French drain

The perforated drain pipe that is chosen really does depend on the size of area you’re installing this system for. For agriculutral applications and big areas it may be prudent to look at twinwall surface water pipes as these come in large diameters. For domestic and small commercial projects though you can opt for perforated land drain coils as they have a range of 60mm to 200mm diameter sizes.

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How do you install a French drain?

French drains are fairly easy to install for domestic and for larger purposes. This step-by-step guide to install a French drain contains just 6 steps!

Step 1: Dig a trench wider than your chosen perforated pipe at a 1% gradient

Choose a location for this trench that’s naturally downhill or create your own slope by digging the trench at a 1% gradient. This will allow gravity to do its part in draining the water away to your chosen destination. The trench needs to be wide enough to accommodate the pipe with an aggregate surround and a layer of membrane too.

Step 2: Lay a water-permeable landscape fabric in the trench

For this you must lay the fabric right to the bottom of the trench and up the sides. Keep enough fabric on either side of the trench to lay over the pipe, almost like wrapping a present!

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Step 3: Fill the bottom of the trench with aggregate

Use a standard landscaping aggregate to fill the bottom of the trench to around a third. Large aggregate will keep the water flowing quickly and with potentially less blockages as any pieces of debris that manage to get into the system will flow through gaps in the aggregate. Aggregate that’s 1cm to 2cm across is generally ideal.

Step 4: Lay the perforated pipe

Lay the chosen perforated pipe with the perforated holes face down in the trench. If you lay the pipe any other way then the water will be unable to leave the pipe until the pipe is fuller, getting rid of the point of this French drain in the first place. Use strong and stable pipe connectors and couplers to extend the French drain beyond the capacity of one pipe.

Step 5: Place more aggregate into the trench

Shovel or tip more aggregate, of the same size as before, on top of the pipe in the trench. This should be until the gravel is about 10cm from the top of the trench.

Step 6: Cover the entire French drain with the remaining fabric

The landscape fabric that should be sticking out of the edges of the trench should now be wrapped over the aggregate and pipe, ensuring there’s minimal (or no) gap between the edges of the fabric. This will prevent debris from entering the drain and clogging up the system.

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Step 6: Hide the French drain

You can choose to place a layer of soil or similar over the French drain without concealing the fact that this in there, perhaps useful in agricultural applications where locating the French drain is important and the look of the land is not. As above, after the landscape fabric has been wrapped around the system, somebody has just installed a layer of decorative aggregate. For domestic and commercial projects, including gardens, parkland and other similar areas, you can cover over this area with grass, furniture, or anything such as this to disguise the work.


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As always, Drainage Superstore is here to help! Feel free to contact our drainage experts on 01752 692 221 for unbiased and free information, advice and guidance on installing a French drain. Whether you need guidance on which product is most suited to your application, or you need clarity on the above steps to installing a French drain, contact us Monday – Friday 8am – 5pm or use our live chat in the bottom right.