How to Build a French Drain: A Step-by-Step Guide

French Drain

A french drain may be the answer to your problem of pooling around the outside of your house, or if you occasionally notice dampness in your basement. These types of drains can be among the best defenses flooded basements, and combined with a sump pump, a french drain is an extremely effective method of keeping unwanted water out of your home.

What is a French Drain?

The basic concept behind a french drain is that water flows downhill and follows the path of least resistance. Pretty simple, right? Actually, the implementation is a bit more complex. However, when the job is finished, it's simply a pipe within a sloped trench, filled with gravel that moves water away from your home's foundation.

  • Fun Fact: The french drain was named after a judge and farmer in Concord, Massachusetts. In 1859 Henry French wrote about the french drain in a book that was about farm drainage. 

Types of French Drains for Basements 

Deep French Drain

There are 2 types of French drains that can directly protect your basement from flooding. The first is a Deep French Drain, it's also sometimes called a footing drain because it is at the same level as your foundation's footing and runs along the perimeter of your house.

A Deep French Drain collects the water before it reaches your basement. These are very easy to setup when your house is being built, but can be very difficult and expensive to retrofit on an established home.

On an existing home with tall basement walls it may be necessary to dig a decent distance to reach the foundation's footing. Not to mention other obstacles such as walkways, landscaping, decks and patios will increase the price if you need to work around or totally remove these items. 

There are two options for removing the water with a Deep French Drain. If you are able to achieve enough slope the water can simply drain on it's own. However, sometimes this isn't possible, in which case the water can be collected in a basin within the basement and a sump pump can then pump the water to the drain system. 

Interior French Drain

The second type is an Interior French Drain where the water is collected as it enters your basement. This is typically a better option than Exterior French Drains since they have an excellent track record of keeping basements dry.

There is no doubt that they are easier to install during your home's construction, but if you need to retrofit this type of drainage system, it usually costs far less than adding an Exterior French Drain.

When adding an interior french drain a channel is chipped out of the concrete along the perimeter of the basement floor. Perforated pipe is then placed within the channel which will direct the water to a collection tank within the floor. A sump pump pushes the water out of the basement and into a nearby storm drain. 

How to Build a French Drain For Yard Drainage

Many basements leak because of standing water that pools around the home's yard. A traditional French drain can move the water away from the house. Installing this type of French drain is relatively easy and cost effective.

Supplies Needed:
French Drain Project

Step 1

Check for Utility Lines and Underground Pipes

Whenever you dig outside you should always locate underground pipes and utility lines before starting. Check your areas building codes or contact a city official to mark the areas you should avoid. 

Step 2

Determine the Area to Be Drained

Find where water pools outside your home. These are the areas that need additional drainage to help direct the water away from your house.

One way to be sure you have all the trouble spots is to walk around your house after a heavy rain. Most likely all the trouble spots will be showing signs of pooling. 

Step 3

Determine the Trench Route

Locate where you will be directing the water. Frequently storm drains or ditches are an excellent location for the water to drain. Use caution that the water won't drain on to your neighbor's property.

A good rule of thumb is to select a location that is lower than your home. This isn't always possible, but if it is, you'll be able to use gravity to your advantage. The best performing drains are those that slope roughly 6 inches for every 50 feet.

Landscaping spray paint is an excellent way to plan your trench. Simply spray the path your trench will take and you'll have an excellent visual of where you'll be working. ​

  • A trench should run parallel to your house and horizontally across the slopes.

Step 4

Build a Slope

A downward slope will encourage the water to drain away from you home. In some cases you'll need to create a slope when you are digging your trench. 

When creating a downward slope, use a hammer to place one stake into the ground where you want to begin your trench. Then place another stake where the trench should end. 

Tie a string from one stake to the other and be sure it is tight. Hang a line level on the string​. Adjust as needed until the string is level. Mark the location of the string on the end stake with a pencil.

​In most cases, you should slope your trench 1" for every 8 feet of length. Measure the distance between the beginning and ending stake. Then slide the string down on the end stake to the appropriate distance.  

Step 5

Dig The Trench

Begin digging your trench. It should be 9 inches wide and 18-24 inches deep from the string to the bottom of the trench.

As you are digging your trench, remember to measure the depth. This ensures you have the correct slope.

Once you have dug the trench, line the ground with 3 inches of gravel. ​

Step 6

Lay The Pipe

There are 2 different types of pipe to choose from. PVC with pre-drilled holes or flexible drain pipe which is cut with slits.

PVC can be easily cleaned with pressure or a plumber's snake should it ever clog. It  also tends to have a longer service life. Flexible pipe is less expensive and many people find it easier to work with.

Run your piping over the top of the gravel in the trench with the drain holes facing down. 

Now, fill the trench with 3 to 5 inches of gravel covering the pipe. Place landscaping fabric on top of the gravel. Cover the fabric with top soil and use a hand tamper to flatten the trench surface so that it is flush with the ground.

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