What is a French Drain?

South End Plumbing, Heating, & Air Expert Tips

What is a French Drain?

If you’ve heard the term “French drain” you may have thought it had to do with plumbing or a certain ornate feature of some type of plumbing drain. However a French drain is absolutely nothing more than a ditch in the ground, inset with a perforated pipeline under a layer of gravel. That pipe funnels storm water or water of any sort outside away from where you don’t want it (your foundation, walkways, driveways, crawlspace, etc.).

How Does a French Drain Work?
How Does a French Drain Work?

How it Works
Working somewhat like a gutter collecting rain as it runs off the roof, French drains pipes manage water at ground level. Let’s say that after a rainstorm, water tends to pool in a particular low spot around your home. Rerouting the circulation of water with a French drain would alleviate that problem.

A French drain also supplies a solution for basements that admit water through the structure. In these “damp” basements, water pushes against the foundation and gradually leaks through. With a French drain, however, water near the foundation can be rerouted and transferred elsewhere before even entering the crawlspace.

If water continues to attack your basement regardless of seemingly sufficient outside drainage, then you may need to set up a French drain around your house. Setup involves digging a trench in the dirt along the border of the structure, laying pipe in the trench, and putting in a sump pump to move water from the interior to the exterior.

Digging a French Drain
Digging a French Drain

Digging a French Drain Trench
Whether installed in the yard or the basement, a French drain deals with the exact same principle. A trench is dug with a slope in the direction you desire the water to go; a slope of one inch for every 8 feet in length is typically advised. To determine the proper angle, use a level string tied between stakes, then measure the range from that referral point to the trench bottom.

Since there is a direct relationship in between the size of a drain pipe and its relative effectiveness, make your trench no smaller than 12 inches wide, and aim for a depth between 18 and 24 inches. If you’re setting up a French drain around your foundation to prevent basement wetness, make sure to place the pipe listed below slab or finished floor level.

Installing the French Drain Pipe
After digging the trench, fill it with a few inches of crushed gravel. Cover the stone with water-permeable landscaping material to discourage weed growth. Next, lay piping into the trench. Select one of two types, either stiff PVC with predrilled holes or flexible drain pipe cut with slits. PVC lasts longer, and if you come across a blockage, it can be cleaned with pressure or a plumbing professional’s snake. Flexible pipe, on the other hand, is less costly and easier to deal with.

Selecting PVC? You can attach a 45-degree angle joint to the start of your pipeline and then link the joint to a pipe that can be left standing out of the ground for an easy-access clean-out point. Another important thing to keep in mind in PVC installations: Orient the pipe holes downward. Counterproductive though it may be, French drains pipes work by enabling water to flow into them from below rather than above.

Wrap landscaping material around the pipe to keep dirt and roots from blocking the system. Infill the trench with gravel to grade. Infill with gravel to a point a couple of inches below grade, then include dirt to span the remaining distance. Covering the pipeline makes complex future upkeep efforts, doing so enables the French drain to be totally concealed.

Bonus Info on French Drains

  • If you are preparing to dig a long trench, think of leasing a trench digger to make quicker work of it.
  • Instead of wrapping the drain with landscaping fabric, you can buy a flexible perforated pipeline that comes already wrapped in water-permeable fabric with Styrofoam peanuts.
  • Install a catch barrel at the end of your drain as a way of gathering rainwater for usage in the garden.
  • After trenching, you can anticipate to have a lot of extra dirt. Plan ahead to use that dirt in the garden or low spots in your yard.

South End Plumbing specializes in all repipes, so remember, we are just a click away. We also specialize in leak detection – give us a call! South End Plumbing is one of the only companies that will give you a free estimate. Call us at 704-919-1722 or fill out the form online to schedule a visit.

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