Project Guide

How to Install a French Drain

1
Plan the Location
A flag in the grass marking a gas line.

Figure out the where the excess water is pooling and where you want it to go. 

 

  • When choosing an outlet for runoff water, look for retention ponds or other bodies of water, or tap into existing drainage. You can divert the runoff water to the road curbside if that's easiest. 
  • Do not drain onto a neighbor’s property. 
  • Use striping spray paint, stakes, flags or another method to mark the direction and length of the trench. 
  • For proper drainage, the trench and pipe system should always drain from a higher elevation and let out water at a lower elevation. 
  • Always direct the water away from your home. 
  • Before French drain installation, make sure your neighborhood has no zoning restrictions and get necessary permissions. 


Tip: Confirm that your water issue is not caused by leakage from underground pipes that need repair. 

2
Dig a Trench
A French drain trench dug along the edge of a fenced-in yard.

Dig a trench from the place in your yard that needs drainage to your chosen outlet.

  

  • Check for underground utility lines and pipes before digging.  
  • The trench should be about 18-inches deep and 9- to 12-inches wide.  
  • French drains need to have a slope of at least 1% so the force of gravity will work for you. This means that the drain should slope down a total of at least 1-inch for every 10-feet of pipe. 
  • Depending on the size of your trench, either dig the trench with shovels or rent a trencher.
3
Line Trench with Filter Fabric
A French drain trench lined with landscape fabric and gravel.
  • To keep the French drain free of dirt, silt and tree roots, lay water-permeable filter fabric or weed barrier over the gravel bedding in the trench.  
  • Leave the filter fabric open with at least 10-inches of excess fabric at the sides. 
4
Pour Gravel Bedding
A trench lined with landscape fabric and filled with gravel.
  • Pour and compact about 3-inches of gravel or landscaping stone along the bottom of the trench. This will act as bedding for the drainage piping. 
5
Hook Up Pipe Connections
A person connecting French drain piping.
  • Install an inlet grate at the point where the water pools the most.  
  • Secure as many fittings as necessary for your pipe system to extend from the inlet grate to the water outlet point. 
  • You can use inexpensive, flexible drainage hose if you need a curved drain, or longer-lasting PVC pipe if you want a more durable system. If you choose the latter, drill holes about 6-inches apart along the length of the pipe. 
6
Set Pipe Drain in Trench
French drain pipe partially laid in a trench.
  • Lay the connected pipe structure in the trench on top of the layer of crushed stone, and make sure the drainage holes in the perforated pipe are pointed downwards.  
  • Test the flow of the drain by pouring water in the inlet grate. 
7
Cover With Gravel and Filter Fabric
A French drain pipe opening peaking out of a mound of gravel.
  • Cover the pipe with about 3-inches of gravel or crushed stone, but not enough to cross above ground level.  
  • Wrap the excess filter fabric over it for another layer of protection. 
8
Backfill With Topsoil
A person filling a trench with topsoil.
  • Fill the trench with topsoil and compact to completely cover the entire French drain system. 
  • When filling the area around the inlet grate, temporarily cover the grate to prevent any stones or soil from falling in after installing the French drain. 
9
Ongoing Maintenance
A French drain system hidden underneath landscaping stones.
  • Reseed the surface if necessary or cover with landscaping stone. 
  • Regularly inspect and clean the inlet grate and outlet point. Flush debris when needed to ensure unhindered water flow. 
  • If your French drain breaks or gets clogged, you may have to dig up part of it for inspection or repair, which is easier if it’s covered with landscaping stone and not grass. 
10
Alternative Method: Gravel-Free French Drainage System
A person installing a gravel-free French drainage system.

To save some steps in the process of French drain installation, consider purchasing an alternative, gravel-free drainage pipe system. This system uses corrugated slotted pipe surrounded by polystyrene aggregate that is then wrapped in filter fabric. 


If you choose this approach instead of manually building a French drain, skip the filter fabric and crushed stones steps listed above. Just place the product in the trench following the manufacturer’s instructions and cover with soil. 

While digging the initial trench can be labor-intensive – try to get friends and family to help, if possible – installing a French drain is a relatively straightforward process that can get runoff water under control, protect your basement and keep your yard from becoming a swamp. 


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