French Drains [Illustrated]

French drain

If you’re having trouble with groundwater or poor drainage in the garden, then we have a solution for you. It’s inconspicuous and works like a charm. French drains do not come from France but were invented in the sunset years of the 19th century by the American lawyer Henry Flagg French who apparently was also an avid farmer. The first designs didn’t feature a pipe at all, but instead roof tiles arranged in a peculiar way. Needless to say, the modern designs are not at all as prone to being clogged with soil and roots. Read on!

What are French Drains?

French drains, or weeping tiles as they are sometimes called, were originally trenches filled with rocks or gravel to divert water by way of providing it with a path of least resistance. Nowadays they are built with a pipe perforated on the bottom to increase the volume of water that can flow through them. This gets rid of the problem of soil clogging up the space between the rocks the original design has. Landscape fabric is also used for additional protection against this, making it possible to grow turf above the french drain.

Тhe main purpose of french drains is to collect surface water and groundwaters and divert it away from the foundation of your home to prevent moisture seeping into it. They are usually set up at the same time as a new house foundation is built if the area is known to have an abundance of groundwater. French drains can be installed both around the foundations or under the basement. The second is usually done when moisture is expected to creep into the house through the basement floor. The pipes laid under the basement capture the water before it even reaches the foundation and leads it away.

Alternatively weeping tiles can be used to:

Improve the drainage of your garden in an efficient and inconspicuous way.

Relieve pressure on retaining walls caused by groundwater.

Lead water away from roads and driveways

Variations

  • curtain drain – This variation is what we mention earlier. While the traditional French drain is open so water can use a perforated pipe surrounded by gravel. This variation is similar to the traditional French drain, the difference being that the traditional is open so water can clearly flow into the gravel. The curtain drain has a lair of soil atop that which can be used for turf or planting.
  • collector drain – It combines groundwater drains and surface water run off. Filters must be installed on the drains that collect surface water to prevent the pipes underground from clogging. This is an efficient way to quickly divert rainfall or any kind of water run off from the surface to underground plumbing.
  • fin drain – The drain pipe has a fin extending above it. The fin is made of draining composite and sucks up moisture from the ground, delivering it to the pipe it extends from. These are the most advanced types of french drains and are actually cheaper to build as both the pipe and the fin cannot be clogged by soil and thus the need for backfill material is reduced. This naturally saves both time and money when building the drain.

How to install a french drain


Before you start:

  • Check if the law allows such a project to be done in your backyard and the appropriate channels to run it trough. It may be annoying to deal with bureaucracy sometimes, but if it’s worth doing the right way.
  • Ensure there are no running power lines or piping through the spot where you’ll be digging. Once again, consult the municipality.
  • Consider whether your french drain will be bothersome for your neighbors. Groundwater run off in another person’s property can give them grounds for legal action against you. Ideally, you want to choose a runoff area away from any buildings and private property.
  • Find an incline. For the drain to work, the piping should be sloping at a 1° angle. If there is no natural sloping you can create an artificial one by gradually digging deeper. This can be done by planting down stakes along the path of the drain and length of rope between them. Then using a string level gauge the incline. If you are not sure how to do this yourself it’s best to hire a professional surveyor.

What you need for your french drain:

Supplies needed for a french drain

  • Shovel – This, of course, is the bare minimum and it may be a backbreaking labor digging the entire trench by hand. However, it’s also free. Fees for a backhoe and an operator for it can cut deep into your budget.
  • Gravel – It’s important the gravel you use for the project is washed. The tiny particles sticking to it may end up in the drain pipe.
  • Perforated pipe – The size of the pipe will vary depending on how severe the drainage problem is. There are flexible varieties too, but their durability is lower and they tend to be more difficult to unclog should the need arise.
  • Landscaping fabric – It will keep soil, roots, and other small debris from clogging up the pipe. There are specialised pipes that come with a landscape fabric “sock” built up into the design.

Step 1 – Dig the trench

dig a trench

Start by digging a trench for the french drain. The size is not set in stone and can vary depending on the function you need. For groundwater draining a deeper trench would work best, while rainwater will drain more easily if the drain is closer to the surface. Ensure the trench does not have any grooves and bumps as these will cause water to pool in them and prevent the proper drainage.


Step 2 – Line with landscaping fabric

line the trench with landscaping fabric

The landscaping fabric will prevent any soil and small particles being washed into the drain’s holes and pipes and clogging it while permitting water through it.


Step 3 – Put down a gravel bed

gravel bed for the french drain

Shovel around 5 centimeters of gravel on top of the landscaping fabric to prepare the pipe’s “bed”.


Step 4 – Lay the pipe

lay down the pipe

The pipe’s holes must be pointing down. This may seem counter-intuitive at first, but this is the way to make it work best. If they are pointing up some water will get into them, but most of it will pool beneath the pipe. Water always chooses the path of least resistance and what your drain does is provide one for it. It will “climb” through the holes of the pipe and follow it to the run off spot. There are different types of pipes, some of them punctured all around the pipes’ diameter. Consult the hardware store assistants to find out which one is best for you.


Step 5 –  Fill in gravel

wrap the fabric around

Shovel the gravel over the pipe until it almost fills the trench. It’s important to live some space to fill back soil. Now unpin the landscaping fabric and wrap it around. This way you ensure the french drain is protected from small particles from all sides.


Step 6 – Final touches

finishing touches

Now you can choose what to do with the remaining space. You can either fill up with gravel, which will make rainwater draining easier or just fill it back up with soil and plant turf over it.  The point of wrapping the drain with landscape fabric is to minimize maintenance and ensure you won’t have to change piping for at least a few years. Which also mean if you choose to plant turf above, it won’t be disturbed for quite some time.


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