How to install a French drain

Most homes already have good drainage in place: gutters, downspouts, and trenching. All these methods are essential to deflect rainwater from the roof and to keep it from creating a sheeting effect off the eaves.

However, you may see pooling water in low-lying areas around the home's foundation or in the yard. This indicates that the soil, the landscaping incline, or standard runoff deflectors are not handling the drainage.

What may be required is a French drain. The good news is that it is relatively simple to install and can be done in a weekend if you have a little help.

A good French drain system will divert the water away from the house and flow into what is called a soakaway, or drain field. This is an enlarged area where the actual piping will end. It is downhill from the soggy areas. The soakaway can be on the surface or can be a depressed area filled with gravel under which the pipe is buried.

The soakaway will be your starting point when you create the drain's path. You will need to mark off the course your drain will take from the soakaway to the point where you want to begin diverting water. You may have a straight line or it may weave among trees or around flowerbeds. If you are designing the system specifically for foundation drainage, it should start at a mid-point in the highest area and then jointed around both sides of the house.

Once you have the pathway marked, check with all utility companies to make sure you won't be cutting into any underground lines. If the area is clear, you may still have some obstacles such as tree roots that may cause a slight change in your drain path.

Next, measure off the length and calculate how much drainage pipe to purchase. If the path weaves from front to back, purchase the flexible 4-, 6- or 8-inch pipe. If your path is straight or jointed at 90-degree angles, then you can use rigid pipe. Drainage products will have regularly-spaced holes along one side. This is the side that will point toward the ground when you lay it in. Purchase the proper connectors and fittings and make sure you know how to make the attachments.

You will also need enough landscape mesh to cover the bottom and sides of the trench and wrap around the pipe.

The intent is to:
-dig a trench
-add a layer of gravel
-spread the landscape mesh
-lay the pipe
-cover with gravel
-cover with sod or paving stones

Now you will need to pre-order gravel. This will be scheduled for a weekday as most gravel companies don't deliver small amounts on weekends. It should be clean, washed stone in sizes ranging from marbles to half-dollars. Gravel with dirt and debris mixed in will cause the drain to clog in a hurry.

You will also have to determine how deep to dig the drain ditch. From the water's entry point the trench has to be directed downhill. If you are concerned about surface water only, then a 12-inch-trench may be adequate. If you are also diverting sub-surface water, then you'll have to dig a deeper trench. Start at eighteen inches and look for seepage. If you are building the drain and it has not rained in some time, you may have to wait and watch. As soon as you get a sizeable downpour, you ill be able to judge if the trench is deep enough. If water begins seeping through the walls of the trench, then you will have to dig deeper. If it does not retain water, then the trench is deep enough.

Add a shallow layer of gravel the length of the trench. Now, place the landscape cloth so that it drapes from side to side. Place the pipe on top and wrap with the cloth. Make sure the pipe holes are facing downward. These will collect any water coming up from underground and allow it to flow to the soakaway.

Fill in with gravel. You can add dirt and sod on top of the gravel if the drain is intended to collect water from a particular starting point. If you have several soggy areas and want them to drain faster, leave the gravel as the top layer and use the area as a walkway or decorative border for other plantings.

French drains do not last forever. At some point, clogging will occur. You may be able to use a router to solve minor problems. Some sections could require replacement.

French drains are essential to the health and well-being of a home's foundation. Once installed, they will protect from the serious damage that water can cause.