Our French Drains, (Trench Drains, or Sub Drains) are designed to collect ground water not surface water.
In many cases foundations and crawl spaces are exposed to ground water. When the ground is exposed to water, such as rain or sprinkler water, that ground can become saturated or muddy. Once the ground becomes saturated most of the water will run on the surface and can be collected with a Surface Drain System. However, a portion of the water that lands on the ground will penetrate the surface. Once the water penetrates the surface it will typically penetrate only a few feet before the ground becomes too dense. The water then accumulates and begins to travel horizontally down hill or to spread out across the area. Since the area under a house or slab is lower than the surrounding area, the water can migrate into these low areas. A French Drain System will intercept and collect that water, preventing it from saturating the crawl space, under slab area, or the soil supporting the foundation.
Our French Drain Systems start approximately 2’ to 3’ away from the foundation; this is to prevent weakening the soil supporting the foundation. The French Drain System is dug to a minimum depth of 12” below the adjacent crawl space, normally a starting depth of about 30” to 36” deep. A 9” wide trench is dug and is line with filter cloth. This filter cloth is designed to allow water to enter the system while keeping out dirt and debris. A 4” PVC perforated line is placed in the bottom of the trench with the holes down to allow water to enter the pipe and flow away faster. The trench is then filled with a washed ¾” drain rock to within 6 to 12 inches of the finish grade, the filter cloth is then folded over the rock and the balance of the trench is filled with dirt. In most cases we install a Surface Drain System in the same trench. A system with both the French Drain and the Surface Drain together is the most effective.
Note: ADS or the flexible type pipe should not be used except as a temporary pipe above ground. These flexible pipes are likely to catch twigs and/or debris and become clogged. Once clogged drain-cleaning companies cannot use traditional rooter type cleaning equipment, as they will damage the pipes. ADS or flex pipes leak at all connection points (much like old clay sewer pipes), which attract roots that clog the pipe. Additionally these pipes are much softer and more likely to be damaged by roots or other forces.
Another “quick fix” solution of questionable effectiveness is the use of “sleeved” pipes of various types. These will collect water only in the area of dirt they displace.