French Drain - Knowledgebase Question

Parsons, Ka
Question by jgbow4751
April 19, 2010
We have so much clay in our front bed the water won't drain, so we plan to put in a French drain. I've read several articles and they say not to place one close to the house, but at least 4-6 ft away or the drain acts like a vacuum and pulls the water to the house. We had planned 2 drain pipes one near the house and one about 5 ft out. Do we need two pipes?
Thx. Gina Bowman

Answer from NGA
April 19, 2010


I'm not sure I agree with what you've read about keeping a drain 4-6' from the foundation of your house. It's a common practice to put weeping tiles or drains right next to the foundation to move water away from the foundation, especially if there is a basement. You might want to get second and third opinions on this before proceeding... As for installing a French drain, it's quite simple: in essence they are just trenches filled with gravel, with sand on top of that. Often, you'll see French drains defined to include a drain pipe as well, though the traditional design is simply the gravel-filled trench. The advantages of French drains are low cost and easy installation. In addition, they can be covered over with turf after installation, making them less conspicuous.

A French drain starts with digging a trench. The depth and width of the trench can vary, but 5 to 6 inches wide and 8 to 12 inches deep are common sizes and usually satisfy most needs. Grading is a critical consideration ? you must ensure that enough slope exists for the water to actually flow, and flow in the right direction. It might be adequate to check very short stretches of drain with a level to ensure that a slope exists to carry water in the desired direction. However, you should take whatever measures are necessary, including a survey and grading, if needed, to ensure that you have at least a 0.5 percent slope. A 1 or 2 percent grade is better. Add gravel to the trench to within a few inches of the surface. Gravel for this use is typically 0.5 to 1 inch in size. On top of the gravel, lay at least 3 or 4 inches of coarse sand. This provides a medium in which turf can grow so that the trench will not be visible. But remember that the sand must be coarse or it won't allow water to properly drain through. If you choose to landscape the area with flowers or shrubs rather than turf you can plant within a foot or two of the trench then cover over everything with bark or other organic matter to hide the trench.

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