Why is my French Drain not working?

Offering reliable landscaping services to homeowners in British Columbia since 2013

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Natasha Maerz

Owner/Office Manager

French Drains are a fantastic option for anyone looking to dry up their yard, but what happens when the system that’s been installed stops working?

This article is going to touch on reasons why your French Drain may not be working to its full potential, and what you can do to fix them.

The issue that most homeowners face when having a French Drain system installed, is that they want their yard to be usable right away after a rain event. A well performing French drain system will dry up your yard within 12-36 hours after a heavy rain event. If your yard is not dry after 12-36 hours after rain, you could have one or more of the following problems.


What area of my yard should my French Drain be installed in?

When having a French Drain installed, your trench should be placed in the lowest part of your yard. This way any water from rain or your roof will be forced to go into your trench where it can then be carried away. If your French Drain is placed at the highest part of your yard, water will not be able to make it into your drain because it will naturally gravitate to the lowest point in your yard.

Why is water pooling in my yard?

If your yard has heavy clay soil, water won’t be able to find its way into your trench, and will sit on top of your lawn, causing it be wet, unless you have healthy establishes grass (we get into that later). If you replace your clay soil with sandy soil or grow healthy grass, the surface water will be able to easily percolate through the soil, and into your trench. Once the water makes it to your trench, the system can take it to its dedicated discharge area.

What can I do make my lawn dry out quicker?

While French Drains dry out within 12-36 hours after a rainfall, if you want to dry out your yard even quicker, you may want to upgrade your system.

A drain grate can be added to your French Drain system to allow water to flow directly into the trench, and let the water be discharged faster than having to wait for it to go through the clay or sandy soil, and then into the system. 

Another option is to actually leave your trench open. Leaving your trench open (not backfilling with soil) means that the water will be able to find your trench right away, and the exposed rock adds a nice décor element to your space.

The option of leaving your trench open is a good one for homeowners who have an open space in their yard, with little vegetation. If your yard has a lot of trees around the area, an open trench may cause you problems, due to leaves and other dirt and debris getting into the system. This debris can clog the rock, and not allow the rock to drain the water going into your trench.

Should you use filter fabric with a French Drain system?

Filter fabric, or landscape fabric, is used in a French Drain system to keep soil from getting into your system and mixing with the round rock in your trench. This is important, because keeping the round rock clean is essential to keeping the void space in your trench open, and to allow the water in your trench to move freely and to the discharge station quickly. Your trench needs void space to allow air to move openly around the trench, therefore creating an underground drying effect. Proper fabric allows all of this to happen. Not all fabric that is used for French Drains are equal, so if your system has fabric but is still not performing well, it could be that your fabric has not been tested for a high-water flow.

Is it bad if my French Drain does not have fabric in it?

 If your system does not have any fabric, you are probably running into an issue of your pipe being clogged with dirt and debris. This dirt clogs up your pipe, and water will have a harder time getting to its discharge area. Putting in a tested filter fabric will protect your pipe from getting clogged, and move the water in your trench faster.

Healthy grass and French Drains

One of the reasons homeowners want to fix their water issues, is so that they can have a nice lush lawn. While grass needs water to survive, too much water can prevent it from growing because it is waterlogged and suffocating, and ironically enough, your lack of grass is one of the reasons you have a wet yard!

Healthy grass roots and vegetation are what help water pass through your soil and into your French Drain 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. Simply put, the healthier your lawn is, the better your French Drain system will work.

What type of pipe should I use for my French Drain?

The type of pipe that is used in your French Drain system is one of the biggest things that will make or break how your system functions.  Perforated pipe (Baughman tile), or pipe that has holes all around it, allows open air exchange to dry out the subsoil faster than any other pipe. This pipe can be put directly on the bottom of the trench, which will ensure that no standing water is left in the trench.


When PVC pipe is used instead of perforated pipe, it needs to be placed on top of rock so that the holes in the pipe do not get clogged with debris. Because the pipe is not placed on the bottom of the trench, some water is not able to make it into the pipe, causing standing water. Standing water is a problem, because any tree or plant roots nearby will look for that water, and will infiltrate the system. Once this happens, it’s only a matter of time before your pipe is clogged, and will need to be replaced or cleaned out. PVC pipe is also prone to crack from frost heave, and when the ground settles.

What material should be used to backfill a French Drain system?

An ideal backfill for a French Drain system is 1 ½’ round rock. 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 then 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.

How to choose a layout for my French Drain?

The layout of the pipe and how much pipe is placed in your French Drain system is important because the pipe that is in the ground absorbs surface and subsurface groundwater, and makes it disappear to the designated area. The more water that gets into your system, the dryer your yard will be. This means that the more pipe that is placed in your yard, the better the drainage system. The best layout is different for each yard and space. An example of a great layout for a yard can be seen below. This layout will allow the water more opportunities to get into the pipe, and away from your yard.

French- Drain- design- layout- 3

What type of discharge station should a French Drain have?

A discharge station is where all of the water from your trench ends up, and a common reason that your French Drain is backing up could be that yours may not be established correctly.  

Your discharge station should be big enough to handle all of the water that is being taken to it, and needs to be placed at the lowest point of your yard. It is up to nature where your discharge station is placed, so if it is not possible to put one in the lowest spot of your yard, water will not be able to reach it. Because of this, a pump will need to be put in to allow the water to get from your trench to its discharge station.

Other options for a discharge station if your yard will allow include a ditch, sump pump, or even a low area in your yard that you do not use that you can flood without it affecting you. Whatever you choose, it must be able to do its job of collecting the water, otherwise your French Drain will not be able to live up to its full potential.


As you can see the methods and materials used to build your French Drain (pipe, rock, fabric) can make a huge difference in how dry your yard will be.


If you think you may need to replace your existing French Drain and are curious about what it is going to cost, get in touch with us!