What Is A French Drain System?

French Drains in Your Home

French Drains have nothing at all to do with France. Their name comes from Henry Flagg French from Concord, Massachusetts, who invented them in 1859. In simplest terms, they are trenches filled with gravel that act as conduits for water runoff. They remain popular ways to remove unwanted water from our basements, as Mr. French originally intended.

anatomy of a french drain system

What’s in a Name?

French drains used to have other names like weeping tile drains, soakaways, rock drains, rubble drains, perimeter drains and even French ditches. These terms originally described the different methods of constructing them. These days, the term “French Drain” applies almost universally, although not all French Drains follow the same design. They all do exactly the same thing though, and that’s to lead water away when it’s not wanted.

Methods of Construction

Before the advent of Henry Flagg French, people dug ditches to take water where they wanted it. These ditches had two disadvantages. They became blocked. Moreover, livestock and people fell into them (and sometimes even drowned). Boarding them over changed nothing except that it became more difficult to clear the stoppages.

Mr. French stumbled over the idea of filling drainage trenches with medium-sized stones. This solved both ditch problems simultaneously because:

  •   Blockages occurred at the entry point and were cleared easily
  •   There was no longer a hole to fall into

The final stage was to fill in over the stones with compacted earth (or even concrete). After that, people seldom even knew the French Drains were there.

drawing of how a french drain system works

Getting the Water into the Drain

This is not as daft as it sounds. When you allow the surface water to enter the drain naturally from the top using gravity feed, there’s a good chance of it backing up in unusually wet conditions and blocking easily. Engineers solved this problem by introducing perforated pipes inserted into the stone fill. That way, if the water started backing up it simply moved back up the tube.

French Drains also drain soggy ground like bogs and marshland. In this case, the builders apply permeable membranes along the length before they add the stones. Water can then enter the trench at any point along the length, greatly increasing the efficiency of absorption while reducing the possibility of blockages from the sides.

What to Fill French Drains With

You can fill a French Drain with almost anything provided it doesn’t rot, holds back a potential blockage and allows the water to filter through. Material can be anything from gravel through broken bricks and tiles to natural stones. It’s customary to use larger pieces in the center, because this speeds up the flow of water.

French Drains in Our Homes

French Drains are present in many Canadian homes, although their owners may be unaware of them. Common applications include:

  •  Placing them just outside external walls to prevent water ingress
  •  Positioning them under floors to prevent water upwelling
  •  Installing them inside basements, in which case the water flows to a sump pump

Despite the best intentions in the world, nothing lasts forever. Older French Drains do clog up eventually especially where permeable membranes are absent. The symptom of this happening is the gradually appearance of groundwater. The solution is to call in an expert to open them up, clean them out, and then reinstate them professionally.

Do you live in Toronto or the surrounding GTA?  Contact us today for a free on-site inspection and estimate.



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NuSite Group is a Toronto based basement waterproofing and foundation repair company that specializes in Basement Waterproofing, Basement Lowering, and Foundation Repairs. Call us today at 416-622-7000 or 905-731-1228 for a free in-home estimate and inspection.

One Response to What Is A French Drain System?

  1. requests free estimate for installing french drain about 10 ft long beside my house. this is to prevent surface rain water accumulation.

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