Exterior drainage system may be known by different names depending on your location. “French drain”, “weeping tile”, “blind drain”, “rubble drain”, “rock drain”, “perimeter drain”. Whatever it is called, it does the same thing and does it extremely well – drains away ground water before it can get into your basement spaces.
As the water pressure builds up on the outside of below grade walls or foundations of your structure, it will eventually push water through even the smallest cracks or voids into interior space.
As any liquid, water will always move towards lower pressure areas. By installing exterior drainage system, we are basically providing this water a place to go.
To begin, a trench must be dug all around structure perimeter all the way down to the footings. At least four-inch polyethylene perforated pipe should be installed parallel with the bottom of the footing.
Perforated pipe should be covered with at least 18 inches of ¾” gravel (porous soils) or more (50%-60% of the wall height on heavy, non-porous soils).
The non-woven geo-textile fabric is wrapped around gravel and pipe to filter debris to prevent drainage clogging. When installation of exterior drainage is completed, the soil gets backfilled to just above grade level.