When building in a crawl space, French drains are a very effective method of diverting floodwater away from your home. A French drain is a large trench or cavity filled with earth or rock containing a perforated drain or channel that redirects groundwater away from a damaged area. These drains are most commonly found in areas with flat, open land and the soil has relatively low levels of saturation.
Digging a French Drain The first step to installing a French drain is to excavate approximately two feet into your basement, based on your soil depth. The French drain should run approximately six to eight feet away from the house. As you excavate, make sure to keep an eye on where you are excavating to avoid damaging the walls of the basement. The French drain will be placed over the excavated area and should extend approximately six to eight feet underground. It is important to dig deep enough to be able to find any drainage systems, water pipes, or other utilities. Once the material is removed from the excavated area, it will be packed and shipped to a contractor for installation.
Installing a French Drain There are many options when deciding how to install a French drain, depending on your foundation. If your foundation is not rated for French drains, the soil and pack must be excavated around your house, similar to regular excavation. If your foundation is rated for French drains, the soil and pack are excavated around the perimeter of the house, and the trench is then dug one foot below surface level. The French drain is installed inside the existing soil, using a steel kit, and then joined together at the bottom of the trench.
Digging Your French Drain Once you have located your French drain and excavated the required amount of soil, your contractor will be able to give you detailed instructions for the placement and positioning of the drain. The contractor will most likely suggest an option for your French drains that involves a flexible French drain insert that can be connected directly to your sewer mainline. This is often the best option if your foundation has suffered minimal damage and you simply need a simple French drain to eliminate excess water from your basement. The flexible French drains are then installed directly to your sewer pipes, while the traditional pipe is buried in the ground. It is often necessary to place a sump pump or emergency drainage system into the sewer line, if it is situated in an affected area, to remove excess water.
Testing Your French Drain After the French drain has been installed, it is often necessary to test the drain for continued water resistance. A French drain will be completely saturated after it has been in place for several years, but new homeowners should test their drains once a year to make sure they are still effective. The best way to test your French drains is to dig a small hole inside the perimeter wall of the house, close to the main floor level. Once the area has been excavated, a permeable soil probe is inserted into the hole and connected to a machine which provides results in minutes. A French drain is only as good as its weakest link. If your soil is very soft and/or clay-like, your perforations may be damaged by expansion while the drain is in use or by the passage of water during heavy rainstorms.
Unplugging Your French Drain Once your French drain has been tested, and it is found that it is not effective or compatible with the soil surrounding your home, it may be necessary to unplug the pipe and repair the drainage problem. If the water level in the trench is more than an inch, the water should be extracted with a strong vacuum pump or excavator. Once the water is removed, a small hole or channel is left where the pipe was inserted, and this can be used to tamp out the retained dirt, mud, and other debris. If a French drain excavator is not available, a back hanger can be used to accomplish the same goal. Once the clog has been removed, allow the area to dry thoroughly before attempting to re-install the drainage pipe.
Removing Mulch and Tree Roots Digging around your yard may expose pipes, utility lines, tree roots, and other unwanted detritus. This also exposes your French drains and sewer lines, if they are intact. It can also expose buried utility lines, piping, and even cables that run under your yard. Before digging, check to make sure there are no underground metal or electrical hazards. If so, this area must be cleared from any potential threat to your home and/or business.
Once you have excavated, cleared, and repaired the trenches, you will need to remove the excavated soil and dispose of it properly. You should excavate the yard six to eight inches deep, depending on the length of your French drain. Light gravel will be preferred for this purpose, as it is easier to handle and dispose of. Mulch, sand, crushed stone, and filter fabric are other options for disposing of the excavated material.