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Underdrain Systems
 An underdrain is an underground drainage system typically referred to as a "French Drain." The purpose of these systems is to carry excess water away from the foundation toward an assigned permeable area.
Excessive water near the foundation can cause movement of the structure due to shrinking and swelling of the existing soils, especially soils with high clay content. The drain is constructed by digging a trench typically about 2' away from the structure. The depth of the trench will vary depending on the slope of the grade and location of the area where the water is being diverted. The bottom of the trench is then covered with filter fabric before the drainpipe is installed.
Typically, we will install two drainpipes - one 6" perforated sock drain to catch lateral water flow and surface water, and another 6" solid drain to carry water collected from the gutters and downspouts. After the drainpipes are in place, 12" of gravel is placed into the trench over the pipes and fully wrapped with the filter fabric. Then heavy grain sand is placed on top of the gravel up to finish grade. These systems are typically installed near structures that are downhill from neighboring properties at a higher elevation.
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