Easy Digging
How to dig and install a
French drain

How to dig and install a French drain
to collect and move rain water
away from your home

Additional Instructions

Please first read Steps 1 to 4,
beginning with: Lawn and Garden Drainage Guide

This page will provide information on:

How to install a French drain
Ideas for a long-lasting system
Drain pipe and drainage tile tips

Lawn and Garden
Drainage Guide

Step 1
Step 2
Step 3
Step 4
Instructions
Lawn Yard and Garden tools
trenching for a French drain
On this page we will dig into how to install a French drain system to reduce drainage
problems in your lawn, yard or garden. Officially a French drain is a gravel drain with
no pipe. The water just collects and travels in a gravel or stone filled channel that
starts from the surface or just below it. But in modern times, and for practical
purposes, we will consider a French drain to include drainage pipe.

Another difference you will notice here is that while other
drainage guides
recommend fairly narrow trenches for their French Drains - often only 6 inches wide -
my recommendation is that your trenches be between 8 and 12 inches wide for the
following reasons:

  • A wider French drain will last longer
  • The capacity to collect and disperse water is better when wider
  • It is easier to dig and grade a wide French drain, especially when deep

Let’s look at each of these points individually…

A wider French drain will last longer because the primary cause of failure in a
French drain is silting up of the spaces between the gravel by clay and soil – and a
wider system simply has more gravel in it and takes longer to clog up. It is also best if
the French drain trench is wrapped in
permeable landscape cloth (the type water
flows through) and the pipes is covered in
drain sleeve fabric to further slow down
any clogging by clay and soil particles. Digging a drainage system is a big job – be
sure to do all you can to make your hard work last as long as possible.

The capacity to collect and disperse water is better in a wide French drain. This
is a common sense type thing. Think about how much more water can flow through a
10 inch channel compared to a 6” channel. Also remember that we want to allow as
much of the collected water as possible to soak into the subsoil in dryer parts of the
yard, and a length of French drain that is 12 inches wide has twice the drainage area
as a 6 inch wide trench. There are also the
small drywells that you can add to the
bottom of the French drain trench - it is much easier to dig these in a wider trench.

It is easier to dig and grade a wide French drain, especially when deep, because
you can get your
digging tools, hands, and even feet into a deep 12 inch trench –
but not a 6” one. Grading the bottom of trench to obtain the proper slope is also
much easier in a wider French drain, especially when digging by hand. There is also
the issue of using a posthole digger in the bottom of the French drain trench to add
drywells, as mentioned in the paragraph above. For those using a trencher, many of
skidsteer type trencher attachments and a few walk-behind trenchers will handle a
12” trenching chain – ask at the rental yard.

So plan on doing the job well, and therefore only doing it once in your lifetime. Take
a little extra time to dig the wider width and spend a little extra for the additional
gravel that will be needed. It will be well worth it!

French Drain and Drain Tile Installation

A few days before you begin to dig contact your local utility company to have all the
underground utility (gas, water, sewage, electric, phone, etc) lines on your property
located and marked.

In your yard, stake out the drainage system you designed in
Step 3. Read the
instructions at our
Determining Drainage System Slope page to figure out how deep
to dig and what slope the different parts of your system should have..

Before you begin to dig think about how you will handle all the leftover dirt. Installing
a French drain is much different than
normal trenching in that much of the dirt will not
go back into the trench (because of the gravel). Most often people load the extra
subsoil into a wheelbarrow and move it to the road for pickup and removal, or move it
to another part of their property for fill. Be sure to plan to pile the subsoil so that you
do not have to cross the trench with a wheelbarrow. The topsoil is usually piled on
the side opposite the subsoil since it will be spread back over the top of the trench.

Often it is best to start digging at the farthest end of the drainage system, usually a
ditch, the street, a drywell, or other low or dry area you are draining to. This way you
lock in the fixed end and if troubles occur further upstream in the system (like a
boulder or major roots) you can sometimes just increase the slope of the French
drain piping to ride over the top of the obstruction.

So gather your friends and some
good trench digging tools, like the Easy Digging
trenching hoe or azada, and get digging.

Installing the Drainage Pipe and Gravel

Congratulations, you have finished the hard part (designing and digging). It was a lot
of work and you don’t want to have to re-dig again, right? To make your French drain
last a long, long time you need to use these following items:

*  Clean or washed gravel (not crushed limestone - it becomes cement like)
*  
Permeable landscape fabric (they kind water passes through)
*  Rigid plastic perforated drain pipe (
not flexible corrugated pipe - read why not)
*  Correct drain pipe fittings (to allow Roto-Rooter cleaning (read how to choose)
*  
Fabric drain pipe sleeve
*  Downspout leaf seperators: either inexpensive or first class


French drains only fail when the gravel becomes full of clay or soil particles or when
the
drainage pipe becomes full of soil or roots. By using the above items you will
maximize the life of your French drain system and make it possible to easily
clean it
out with a Roto-Rooter or sewer snake if it does become plugged.

Here is what your French drain trenches should look like:
Note that there is always at least 2” of gravel all around the 4” drain pipe. Also note
the fabric drain sleeve and that the landscape fabric is overlapped and completely
surrounds the gravel. Remember that the rigid drain pipe is always installed with the
holes on the bottom.

For information on how to select and install the pipe and fittings for a  
French drain system that works well and can be cleaned in the future go to
the next page:
How To Install French Drain Pipe and Drainage Tile
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digging?

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