|Posted by Charlie on May 06, 19101 at 19:03:14:|
|In response to Re: French drain instructions.|
I've used French drains to keep runoff from the foundation way when it was impossible to slope the land away from the foundation adequately. Just keep the basic principles clear: It's a trench to catch and divert water. Ideally, it could be a wide open trench, but that's usually not practical, so you want to fill it with material that will still let the water move through it and that will keep crud from plugging it up. So:
The bottom level has to slope to direct the water where you want it. So the grade is very important. You cna use a string level (a little level that hangs on a string) to determine level, and then slope accordingly. How much it slopes depends on what is practical in yor situation and how permeable your soil is. A small slope will do in clay type soils. I would then lay perforated drainage pipe or tiles in the bottom. I would have the holes in the lower side. Then fill with crushed stone (3/4 or 1.5 inch) to about 4 inches from the top. This is very stable and water moves through it easily. Near the top, the idea is to keep silt from working it's way down in. I put about 2 inches of pea stone next (small crushed stone). Cover this with geotextile, a permeable nondegrading fabric that water goes through easily, but dirt does not. REeadily available at Home Depot, etc, but you'll have to describe it for them to point you in the right direction. Then another 2 inches or so of pea stone, with some course sand at the top.
Remember that the drain needs an outlet, either on the surfact in sloping land, or a good drywell or two for seepage into the ground.
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