Essential plumbing hacks: French drain installation

If you’ve been noticing signs of water damage in your yard, such as surface water pooling or mold, you ought to be worried. Not addressing these drainage problems over a period of time can lead to permanent structural damage. Fortunately, the solution to these problems is a relatively simple one: installing a French drain.

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What is a French drain?

For the uninitiated, a French drain is a trench with a perforated pipe and gravel that helps water drain naturally from your yard. Installing a French drainage system is a fairly easy process, and this short read will show you how you can do it yourself.

Choose the right location

1. Make sure the runoff water drainage you choose either connects to an existing drain or to a water body like a retention pond. Even a curbside is an option if you don’t have another choice. However, never drain your runoff into your neighbor’s yard.
2. Mark the length and the direction of the drain using spray paint, flags, or stakes.
3. In order for the system to work efficiently, water should always drain into the trench from a higher elevation while the outlet should be at a lower elevation.
4. Always make sure the drain carries water away from your house.
5. Before you begin the project, check with local authorities about zoning restrictions. If you need to get permissions, apply for them well in advance.

Get digging

1. Before you start digging a trench to install your French drain, check with your local utility company for where they’ve laid utility lines. You definitely don’t want to cause any damage to those.
2. The trench should ideally be between 9 and 12 inches wide as well as 18 inches deep.
3. To make sure that gravity works in your favor, maintain a slope of one inch for every 10 feet of pipe. If you don’t get the slope right, your French drainage system will not work.
4. If your project isn’t too big, you ought to be able to dig the trench with shovels. However, if you need a large trench, hire a trencher.

Lining the trench

1. Once the trench is dug, you will need to keep your French drain free of dirt, tree roots, and silt. For this reason. line the bottom of the trench with a water-permeable weed barrier, landscape fabric, or filter fabric. 
2. Be sure to leave at least 10 inches of fabric extra at the sides and to leave it open.

Pouring the gravel

1. Pour and compact around three inches of gravel to act as bedding for the drainage pipe.

Pipe connections

1. An inlet grate must be installed at the point where the water pools the most. 
2. Ensure you secure all the fittings needed for your pipe to extend from the inlet grate to the outlet point.
3. While you could use inexpensive flexible drainage hoses to do the job, PVC pipes will be more durable in the long run. If you choose to buy PVC pipes, drill holes on the surface around 6 inches apart.

Pipe drain setting

1. Lay the connected French drainpipe on your gravel bed with the drilled surface facing upwards.
2. Pour water into the pipe to make sure you have the water flowing in the right direction.

Covering up

1. Cover the pipe with around 3 inches of gravel. However, make sure it remains below surface level.
2. Cover the gravel with the excess filter fabric.
3. Cover the entire French drain system with topsoil to hide it from view.
4. While working to cover the area around the inlet grate, cover the grate temporarily to avoid any stones or soil from falling in.

Maintenance

1. You could cover the surface either with turf or with gravel. Turf will need reseeding from time to time.
2. From a maintenance point, it makes more sense to cover the drain system with gravel, since you will need to replant turf every time you need to dig to get access to the pipe for repairs.
3. Keep the inlet grate and outlet point clean. Flush out debris regularly to keep your French drain system working.

Alternative

There are two types of French drain systems. We’ve just described to you how you can set up the most commonly used one.

The second alternative is installing a corrugated pipe surrounded by polystyrene aggregate covered with filter cloth. To install this variant, you need neither gravel nor an extra filter cloth. All you need to do is follow the instructions in the product box.

French drain installation cost

The overall cost for installing a French drain depends on a number of factors, including the location of the drain, the size, length, and depth of the drain. 

The national average cost of installing a French drain is around $4,500. If you’re looking at installing a 100 linear foot drain in an external location, it might cost you as little as $2,000. On the other hand, a similarly sized perimeter drain installation may cost you as much as $10,000.

Pros and cons of French drains

French drains, like everything else, have an upside to them, as well as a downside. Let’s take a look at the pros and cons.

Pros

1. French drain systems are extremely effective in keeping groundwater away from the foundation of your home, especially if you live in an area that experiences heavy rains. Installing a French drain system is a great way to protect the structural integrity of your home.  This is why they have been around for more than 150 years.
2. Not only are French drains effective, but they are also really affordable and easy to install. 
3. In addition to affordability and effectiveness, French drain systems are also extremely durable. Since they have no mechanical moving parts, once installed, a French drain system can last decades with basic periodic maintenance.

Cons

1. Installing French drains requires excavating your garden. If you have an elaborate garden setup, this may not be the right solution for you.
2. While you could make installing a French drain system a weekend DIY activity, you can be sure that it takes a lot of hard work to actually finish the project. You may be better off hiring professionals, but that will definitely increase your budget.

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Written by Narayan Shrouthy. August 15, 2021

Narayan is a content writer for Kukun. With experience in both content writing and editing, Narayan mixes his writing and love for reading with his passion for music. As an active musician, He aims to be a key player in Kukun's content experience.