Exterior Perimeter Drain

Though mistakenly referred to as "French Drains," exterior perimeter foundation drains are designed to collect the water that accumulates next to the foundation wall and divert the water away from the home.  Clay drainage tiles in older homes or perforated plastic drainage tiles in new homes are placed next to the foundation footer and covered with a minimum of 6 inches of gravel or crushed stone.  The surface water that enters the soil next to the foundation flows down the wall, then following the path of least resistance, flows through the gravel and into the drainage tile or pipe.  The water is then directed to either a storm sewer, dry well or, if necessary, to a sump pump to be directed away from the home.

Generally, the system is only placed next to the one or two walls that experience the water penetration problems.  However, in some severe cases, the system is placed around the entire perimeter.  In addition, to help prevent sediment from entering and clogging the drain pipe or tile, a filter paper is placed around the pipe (especially the openings) or gravel.