French drains, a form of a subsurface drain, utilizes a buried perforated pipe installed in a gravel bed with a geo-textile fabric envelope lining the trench. Water from the surrounding soil enters the gravel bed, flows into the drain pipe and utilizes gravity to flow towards the discharge point.
The three most frequently used type of French drain pipe systems for residential and commercial applications are smooth sewer and drain pipe, corrugated plastic pipe and poly drain pipe. Smooth wall sewer and drain pipe is rigid and manufactured from PVC or Polyethylene. Due to its rigid nature, it is easier to maintain a continuous slope in critical areas by spanning over uneven trenches. Corrugated pipe is manufactured from high-density polyethylene and is available in 10' - 250' rolls. Since the corrugated pipe is flexible, it can follow contours of the ground and wrap around corners without couplings or elbows. Poly drain pipe (EZ-Flow) is a self-contained french drain system that combines corrugated pipe with a poly aggregate wrapped in geo-fabric. This system eliminates the need for gravel and a separate geo-textile cloth.
Each of the above-mentioned drain pipe systems has perforations or slits to allow water in and directing this water downstream to a discharge point. Discharge points can be grates, drywells or popup emitters. French drains are the most common method for evacuating excess ground water which has infiltrated into the soil. If the gravel is run to the top of the trench you can also direct surface water down through the aggregate to the pipe system preventing water in unwanted areas such as near foundations or across patios and sidewalks.
A well-designed and installed French drain system can prevent foundation repairs and basement flooding. By stopping surface and groundwater from coming into contact with foundation components, basements will stay dry and foundations will remain more stable. Understanding water flow and pipe capacities are key components to a well designed French drain system. Many foundation repairs and basement waterproofing contractors have been trained to diagnose and solve groundwater issues, but it is always advisable to consult with a professional engineer when dealing with foundation issues.