The 4 basic French drain principles
- The French drain trench must be dug below the level of the area that is to be drained.
- A gradation of the French drain aggregate (in-fill) or a filtration medium (geotextile fabric) must be installed to reduce siltation of the collection pipe.
- A perforated pipe must be installed to collect and transport the water to the desired location.
- The outlet of the pipe must be the lowest point in the drainage system.
The four basic principles that define a French drain are critical and allow the drainage system to be effective or not (if applied or installed improperly). Each of the four principles seem rather basic, but I am routinely reminded how often one or several of the principles gets overlooked or ignored. So, let’s look at each principle in greater detail: