Common french drains mistakes

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Natasha Maerz

Owner/Office Manager

French Drains are a great option for homeowners that are looking to rid their yard of unwanted water. Like with any project, there are common mistakes that are made during a French Drain installation that can be prevented, or at the very least, solved.

How do we know? We are French Drain experts and have helped hundreds of customers solve their water issues once and for all. 

Table of contents

  • The size of the French Drain trench
  • The placement of the pipe
  • Backfilling the French Drain with soil
  • The French Drain discharge
  • Installing Big “O” drainage pipe
  • No other Drainage solutions present
  • The health of your lawn

The size of the French Drain trench

When digging a trench for a French Drain system, the deeper and wider that the trench is dug, the more surface area there will be within the trench. This is important, as the surface area of the trench is what dries out the subsurface of the yard.

Another factor that helps the subsurface of a yard stay dry are the rock that is used in the system. Big round rock allows a bigger void space in the trench, and this air movement creates an underground drying effect. The big void space made by the rock also acts as an underground reservoir for the water entering the trench. This is particularly helpful when there is heavy rainfall, or large amounts of snow melting at once.

The placement of the pipe

The purpose of the pipe in a French drain system is to “carry” the water away from the area that is water logged. The placement of pipe really makes a difference in how the drain works, and for how long it will work for.

When the pipe is placed on top of the rock, there will always be standing water under the pipe. If you have standing water, tree roots will seek out the water and infiltrate the system. As the roots begin to clog up the pipe, they will need to be cleaned out by a jetting machine. This jetting machine can remove the roots from inside the pipe, but will not be able to completely rid the pipe of them. Days/months later the roots will have regrown inside of the pipe again. Therefore, this cleaning and regrowing will continue indefinitely.

A better drainage pipe to use for a French Drain system would be perforated pipe. Perforated pipe (Baughman tile) is placed directly onto the bottom of the trench that is layered with tested filter fabric, not on gravel or rock. Because of this placement, there will be no standing water in the system, and the water can easily get taken to its discharge station.


Baughman- tile- and- round- rock- in-French-Drain

Backfilling the French Drain with soil

French Drains can be backfilled by either using the excavated clay soil from your trench, or by using 1 ½’ round rock.

If you have drainage issues, and your yard is always wet, it is most likely because you have clay soil in it. If your yard was sandy, you wouldn’t have a water problem, because water can percolate through sand no problem, and not allow surface water to pool. Clay soil does not allow water to go through it, and therefore the water will have nowhere to go.

If you use the same material that you already have in your yard as backfill, you will have the same drainage issues shortly after your system is installed. Yes, a drainage pipe will be put in the ground which should carry your water problems away; however, water has to be able to get into the pipe that was placed. What ends up happening is the system works initially because the clay soil is uncompacted, and allows water to pass through it into the drainage pipe. Shortly afterwards though (2-24 months) this clay soil compacts just like the rest of your yard. Once it compacts again water will sit on the surface of your lawn.


Clay soil disadvantages

  • When there is no void space in the trench the surface of the yard dries slowly, and the subsurface never dries out completely. As we said before, this is because water cannot percolate through the clay soil.
  • Using soil gives your system a short lifespan, as clay soil will compact and not be able to provide the drainage you are looking for.
  • System is Expensive for how long it lasts (2-24 months).
  • Grass roots will be waterlogged due to standing surface water. This will cause a yellowish tinge to your lawn as its oxygen supply is cut off

1 ½’ round rock can be used in place of clay soil to backfill the trench. When backfilling with 1 ½’ round rock, your system will have an ample amount of void space due to the size of the rock that is placed in the trench. Void space in a trench is important, because the greater amount of void space that is in the trench, the quicker your yard will dry. Void space allows both the surface and subsurface of your yard to dry out quickly by allowing air movement in the trench, creating an underground drying effect. The water that is on top of your yard is able to go through the round rock, and into the pipe. Once that water gets into the pipe, the pipe can take it to its discharge station, and your yard will be dry.

The French Drain discharge

City storm drains and ditches usually have enough capacity to act as a great discharge location for your French Drain system. If the city storm drain or ditch are at the front of your house and your system is at the back, more pipe will need to be placed to get to it. Since adding more pipe and labor will bring up the cost of the install, you may want to seek other alternatives, such as a rock pit.

Rock pits are a common method used as a discharge location, but unfortunately, they usually do not have enough space to hold the water that you are trying to get rid of. By early winter your system could get full, and will stay that way for most of the year.

Installing Big “O” drainage pipe


Black ADS brand French drainage pipe, otherwise known as Big “O”, is made up of recycled materials, and has three small inlets sliced in every valley. This pipe is used quite frequently in drainage jobs due to its availability, how flexible it is, and how fast it is to install. This pipe crushes very easily, and allows dirt and debris to get into the pipe, essentially clogging up the system. Once this system is clogged, water cannot get into the pipe, and will stay stagnant.

A better option of drainage pipe to put in this system is Baughman tile. This purposed built French drainage pipe was designed for the clay soil that the Fraser Valley has. It is extremely flexible, fast to install, and has an excellent crush rating. Due to its 8 massive inlets in every valley, there is open air exchange that can dry out the subsoil much faster than any other option of pipe.


No other drainage solutions present

If your downspouts are not connected to a downspout drain, all of the roof water that is being collected in your gutters and downspouts is going to go directly onto the surface of your lawn. This is a substantial amount of water that is being put onto your lawn, therefore causing water to pool on the surface of your yard. Having a downspout drain system installed will limit at least half the amount of water that your yard will have to get rid of after a rainfall. Combine this system with another drainage solution, like a French Drain system, and you have significantly changed how much water your yard sees.

The health of your lawn

Healthy grass is a step that is often overlooked when it comes to installing a French Drain. Healthy grass roots, plants and vegetation are what help the water pass through the clay soil in your yard and into your system. Without an abundance of roots penetrating deep into the clay soil water will sit on top of the lawn regardless of any system that is put in. The roots from your lawn, and plants play a vital role in allowing this water to follow the roots deep underground and into your French Drain.

Annual lawn maintenance will allow your French Drain to continue to work optimally. Annual maintenance for a healthy lawn includes Fertilizing, moss and weed control, aerating, and seeding.

As you can see, all of these common mistakes can easily be fixed if the right materials and methods are used for installing the French Drain system.

For more information on French Drains click here.

If you would like to know how much it would cost to install a French Drain on your property click  here.