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OK, I know how I have done them, but what is the proper way to do a french drain, about 75-100′ long? How deep, ” gravel on bottom, ” gravel on top, silt screen (fabric, shingles, etc). Holes up or down on the perf pipe, what size pipe, etc.
Thanks
Greenjeans
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I've put in a few, and have had no problems. I use 4" pipe and lay them in a bed of 3/4" material. The pipe should be at the same level as the bottom of your footings. I slide the pipe in a porous material made for this purpose. I then back fill the excavation with good gravel.
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My advice is to go to the source--Henry F. French of Exeter NH, who wrote the book Farm Drainage, 1859 first edition. There you'll find what is, I believe, the first mention of Drainage of Cellars.
Three questions: what water are you collecting, how are you taking it to an outlet, and what is the outlet?
1) Are you intercepting major rain percolation through the soil (swale) or threatened rising ground water? If so, gravel, filter fabric and perforated pipe, preferably a PVC pipe system designed for cleanout, maintenance and repair. Only incidental percolation or unlikely ground water? Then a corrugated system at the footing with gravel may be all that is necessary. Downspout discharge? Then any below-grade system should be non-perforated, no gravel, and designed with cleanouts.
2) After the water is collected, then a rigid PVC home run to the sump or daylight. No gravel for the home runs, but instead good compaction around the pipe. You don't want the exterior of the pipe to become a watercourse.
3) If you go to a sump pump, then where does the pump discharge go? Here in the new 'burbs of Champaign IL, the sump discharge can leave the house, then drop below grade to the storm drains at the street--a pretty good system that inoculates the house against city storm backup. If you go to daylight, anticipate rats and mice in the pipe.
*Having had my backyard a spring after El Nino of a few years back (and percolating UP through the slab of my family room) I became the resident expert on French draining. Our house is situated at the foot of two slopes, so we get all the percolated water from many acres of hillside. In emergency repair we dug a trench across the entire property between the house and hill to "intercept" the ground water. There was a river running constantly in the bottom of the trench with pumps at each end (and one in the hole I punched in the floor of the family room).... I calculated that in one 48-hour period I pumped out a little over a quarter-million gallons of water (!!). Anyway, I digress. We ended up with 6" THICK-WALL PVC pipe (don't use the Home Depot white crush-able junk), set on a couple inches of 1" gravel, wrapped in fabric, HOLES DOWN (unless you want the water level up another six inches), covered with gravel to within six inches of the top of grade, covered with topsoil. Come to think of it I had one of my guys drill extra holes on the sides (and maybe tops) of the pipe, too...figuring "why not?".... and, if you can, put a long-sweep elbow at the end and run it up to grade to use as a clean-out in case you get roots or cloggage later; you can cap it with an area drain so it still has function.There...that's all I know about them.... now, why are they referred to as "French"?-Ben
*Basic info, house is on a slope, maybe 12' drop to the street across the 200' depth of the lot. During the recent heavy rains, ground in back, 12+' from the house, was totally saturated -- just muck. Good grass cover, which probably helped to slow the water down, so the soil could absorb even more. Brick patio/walkway extends out from the house 10-12', in a drainage swale. Good slope on the brick away from the house, and down to one end of the house.My thoughts are to put in a french drain, appx 15' from the house, to drain the saturated ground. This will drain to daylight.If this does not take care of the problem, then have a contractor come in, and dig to the basement slab level, reinstall drain -- built in '50s, so is probably Pomona pipe, and also put the waterproofing stuff on the wall before backfilling.As best I figure, if the surface drain works, I'll save a few thousand. If it doesn't, whats one more flood in the basement?Mr. Greenjeans
*Hi Mr. Greenjeans. I think you're definitely on the right track. I would put at least two interceptor drains as your footing drains. Stack them on top of each other a few feet apart to form a footing drain wall or "curtain". Use perforated pipe encased in gravel. Put a slight slope on the drains. Y them together near the end and connect them to non-perforated pipe which you'll run to daylight. In my opinion, I would not dig around foundation and waterproof even if you do have water in your basement. I couldn't tell by our message if you did or not. The interceptor drain should work from the sounds of your problem. Good luck. Al
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Ben -
I think they call them french drains because the water keeps going down on you.
(Maybe I should have posted this in theWoodshed ?)
*Al P., can you define some terms?"interceptor drains""drain wall or curtain"Sketch would be great, if you have a scanner...Explain why you would not recommend to dig around the foundation (due to the cost or concern for damaging the foundation or some other reason).thanks!
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Norm, Sorry, I don't have a scanner. An interceptor drain is a high tech way to say a drain that gets in the way of or intercepts the water. Water is heading down the hill toward Greenjeans and he needs to intercept it. Looking at a drain wall or curtain would be looking a two or more drain pipes stacked on top of each other to provide more space for water to flow. Imagine stacking ten drain tiles(pipes) on to of each other. They'd form a wall. If my basement had water in it and there were no major cracks in the wall then the water is not entering through the wall. It most commonly enters through the cold joint(where wall and floor meet). This implies water pushing in from below or right around the footing. In my opinion, the easiest and least expensive way to correct this is with a basement baseboard system designed to LET the water IN and channel it away to a sump. You want to relieve the pressure to get rid of the water.No diggin, no landscaping and a lot less time. When we build houses, we install exterior and interior drain systems for this purpose and skip the water proofing. Damp proofing(hot tar) is plenty sufficient. It would take a heck of a lot of pressure to push water sideways through a concrete wall especially with gravity in the equation but rising water underneath a foundation is another story. If a basement floods after it's built, it's usually due to this. However, you must analyze it carefully to be sure. That's why i wasn't sure what to tell Mr. Greenjeans because I didn't know if he had water in the basement or not. Hope this helped. Al
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OK, I know how I have done them, but what is the proper way to do a french drain, about 75-100' long? How deep, " gravel on bottom, " gravel on top, silt screen (fabric, shingles, etc). Holes up or down on the perf pipe, what size pipe, etc.
Thanks
Greenjeans