French drains originated in the United States, even though their name would indicate otherwise. Basically, they work by supplying invasive groundwater with a path of least resistance by means of which it can be redirected away from a structure or low-lying area of lawn. They are named after a new Hampshire man, Henry Flagg French, who, in 1860, published a definitive work on soil drainage with the simple and inviting name: “Farm Drainage – The Principles, Processes, and Effects of Draining Land with Stones, Wood, Plows, and Open Ditches, and Especially with Tiles.”
These days, French drains are normally used to fight flooding issues caused by surface and/or groundwater that a home owner may be having, particularly influencing their lawn, foundation or basement. They are additionally sometimes employed to drain off liquid effluent from septic tanks.
The elementary design, a gravel-filled trench, is basic but for it to continue operating indefinitely, it’s crucial that it be effectively executed.
Flooding issues are normally linked with sloping ground, non-porous clayey soil, or a combination of the two. For instance, if your house is located on a slope with your neighbors’ residence occupying a lot farther up the slope, heavy rain can precipitate an accumulation of groundwater rushing down from their property and onto your own. If your soil is not able to absorb all that h2o, you could very well suffer damage to your property’s foundation, or leakage into a crawlspace or basement under the ground floor of the property.
A linear French drain is an uncomplicated, cost-effective solution to this kind of a problem. In the scenario described, it acts as a moat that shields your residence by intercepting the groundwater rushing down the slope and redirecting it around and away from your residence’s foundation.
A linear French drain is doable as a D.I.Y. project, if you don’t mind carrying out some backbreaking labor (it does require digging a trench after all) and you have the proper equipment and materials (1″ round washed gravel, 4″ PVC water pipe with drainage holes, a trenching spade or power trencher and a builder’s level).
O.K., let’s launch right into a more detailed explanation both on how to install a French drain, and how they work. the first step is to dig an L-shaped or U-shaped trench system, 6 inches wide and 24 inches deep, 4 to 6 feet from the home. It’s essential not to install the drain too near the house due to the fact that, if you do, you’ll be bringing moisture up against the house, which is just what your trying to avoid.
The primary leg of the trench system must be dug up the slope from the house. For a U-shaped French drain, it had best be level and linked to two pipes on both sides of the residence with 90 degree PVC elbow joints. For an L-shaped drain, the primary leg should slope down, at a pitch of at the very least 1/8 inch per foot of fall, to the 2nd leg which will run next to the house, also linked using a 90 degree PVC elbow joint.
When you are laying out your French drain, you want to make gravity work in your favor. Just as is the case with an above-ground river, groundwater flows downhill, so you’ll have to work with the natural slope of your property and, if you can, have the exit PVC pipe come out above ground to give the groundwater an simple exit point.
As soon as you’ve worked out the layout of the system and accomplished the major work of digging the trenches, it’s time to assemble the working parts of the drainage system: the gravel and pipes. First, tamp down any free soil in the bottom of the trench and line it with 1 to 2 inches of gravel, lay the PVC pipes on top of this first layer of gravel, with the holes pointing straight down, and then fill in the trench with more gravel, to one inch under ground level. Then all that’s left to do is disguise the trench with sod or another ornamental touch of your own choosing. And you’re done. The next time you experience a downpour, any excess ground water will enter your recently installed French drain and be diverted around your house and discharged at the end of the exit conduit.
You often hear that a French drain should be lined with geotech fabric and the piping be wrapped in a geotech sock to stop it from becoming clogged with silt. I don’t advise doing either. If you were going to use geotech fabric anywhere, the place to put it would be on top of the trench to decrease the chance of silt and sediment from filtering down from above and filling in the air spaces in between the gravel. Most of the water that enters a French drain is groundwater flowing sideways underground, not downwards from the surface. Groundwater is not silty, it has already had the silt and sediment filtered out of it as it trickled straight down through the topsoil. If that seems doubtful to you, just ask your self if underground spring water and well water are clear or muddy. Each of them are of course generally crystal clear due to the fact that earth is a natural water purifier.
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