The french drain is usually installed outside the perimeter footings at ground level. Its role is to minimize infiltration of water under the sole or between the base and the foundation. It is normally connected to a pit inside the basement. The drain can be wrapped in a membrane to reduce access to the solids that can clog. This technique is obsolete because over time, the industry has found that the thin fabric cover is easily obstructed. The recommended approach is to cover the drain and the outer portion of the footing with net crushed stone to improve the flow of water to it. Subsequently, before the backfill, the stone is covered with a 30 inches wide geotextile to limit the contamination of the stone and drain, thus maximizing the drainage properties of the system.
In soils conducive to iron ocher, a bacteria that tends to clog the french drains. It is recommended to replace the black flexible drain with a rigid perforated PVC drain. Then, the drain is covered with stone and stone covered with a geotextile membrane as described above.