French drain – when to use and how to install

French-Drain-Image-Example-What-is-a-french-drain-1

What is a French drain?

French drain, trench drain, land drain, sub surface drains all names for a trench filled with stones to direct water away from waterlogged areas in gardens and from around buildings. Really a simple solution of a channel filled with stones to allow water to flow to a new area and be absorbed into the surrounding soil along its length. They can also incorporate pipes that will directly move water to a designated area.

 

Why is it called a French drain?

Henry French wrote a book in 1859 on farm drainage.

 

Do I need a French drain?

Do you have issues with water building up and not draining away around buildings, it is essential that you keep any water or moisture away from building s and foundations as they can lead to damp and damage to bricks and mortar.  Do you have a retaining wall on a slope? Make sure you install a French drain to stop water running to the bottom and possibly towards buildings.

Where can I build a French drain?            

A French drain must be at least 1m away from walls and foundations of buildings. French drains are usually located along a boundary or alongside buildings.

How do I know if my French drain has failed?

Water pooling in the same or new parts of the garden? Building walls surrounded by water?
French drains can fail for a variety of reasons; the perforated pipes can get clogged up with grit and soil. This can also happen to French drains that don’t include pipes.

Don’t worry they can be flushed out with high pressure hoses. The main thing to do if you think your French Drain is or has failed is not to wait. The longer you leave it the more damage it could do and the more clogged it will get.

What geotextile do I need for a French drain?

Non-woven – perfect for filtration

Geotextile-Membrane-Gravel-Example

What do I need to install a French drain?

Shovel- to dig the hole

geotextile membrane – to help with filtration and stabilisation of the drainage channel

gravel – to fill the drain

perforated pipe if you have a site in mind for the moved water e.g., A well it is best to direct it specifically using a pipe. Pipes are not necessary in all French drain installations.

Ready and willing helpers to help with digging and filling – payment or biscuits always helps!

Gardening-Example-about-us-page

How to install a French drain?

  1. Plan the drain – where does it need to drain too?
  2. Check distances and measurements from buildings and depth of drain needed.
  3. French drains do not need to be massive 300-500mm depth 200-300mm width.
  4. Dig out the soil for the channel, keep the sides sloping towards the base.
  5. Lay a non-woven geotextile along the dug channel and up the sides.

https://spudulica.co.uk/product-category/drainage-and-soakaway/

 

  1. Fill drain with aggregate/ gravel
  2. If adding perforated pipe fill the whole 1/3rd way up then lay in the pipe. Make sure the pipe is also wrapped in geotextile membrane or pipe sleeve. Then continue to fill drain.
  3. Cover in finer aggregate
  4. Tamp down lightly to get finer aggregate in place but not compacting your drain.
  5. Wait for rain and see those waterlogged areas draining nicely.

How do I know if my French drain has failed?

Water pooling in the same or new parts of the garden? Building walls surrounded by water?
French drains can fail for a variety of reasons; the perforated pipes can get clogged up with grit and soil. This can also happen to French drains that don’t include pipes.

Don’t worry they can be flushed out with high pressure hoses. The main thing to do if you think your French Drain is or has failed is not to wait. The longer you leave it the more damage it could do and the more clogged it will get.

 

 

Give us a call on 0151 515 1415 or email hello@spudulica.co.uk if you need any advice,

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