What is a French drain?

The French drain is a drainage system placed at the base of the walls of building foundations covered with a layer of gravel.

This drainage system is used to evacuate groundwater and water from the surface. It avoids the accumulation of water behind and under the walls of foundations and the slab on the ground.

The drain has a life span varying between 25 and 30 years. It depends on the type of soil and embankment. It can clog after only a year if there is a fine clay soil.

The installation of the drain plays a key role for its proper functioning. An improperly installed drain equates to a non-existent drain.

Signs of lack or improper installation of a drain

  • Presence of mold in the basement;
  • High humidity in the basement;
  • Efflorescence at the base of the foundation walls;
  • Presence of star-shaped cracks in the slab on the ground;
  • Efflorescence on the slab on the ground;
  • Water infiltration towards the inside.

The problems often encountered with the French drain

  • Negative slope of the drain;
  • Installation of a French drain in the shape of a zigzag;
  • Drain hose away from the sole or higher than the base of the sole;
  • Lack of gravel and the presence of very fine clay soil;
  • Drainage pipe crushed or clogged.

When installing a French drain, around a building, you must examine the foundation walls, repair cracks as well as damaged areas in the concrete if necessary. In addition, the excavation must be backfilled with appropriate gravel, exterior landscaping and all related work.

Onesta Building Council

The engineer at Onesta Bâtiment Conseil does not himself inspect the French drain by camera. Indeed, this test must be carried out by a plumber, equipped with a video camera, who makes his comments on the video by specifying where are the areas examined section by section.

The building engineer, according to his mandate, can analyze the data collected by the plumber and express his professional opinion concerning the state as well as the deficiencies relating to the French drain.

According to the mandate, our civil engineer can therefore:

  • Analyze the data and express his professional opinion;
  • Write an expert report with photos, diagrams, findings and recommendations;
  • Produce plans and specifications for corrective work.

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French drain blocked by ferrous ocher

French drain blocked by ferrous ocher