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Old 04-23-2011, 02:29 PM   #1
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indoor french drain

how many inches of stone need to be laid before layinf pipe down??


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Old 04-23-2011, 04:15 PM   #2
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indoor french drain

The usual recommendation is two inches.

Before putting down all the stone, lay down the porous cloth that is used to keep dirt out of the pipe. For example, with a 2 inch layer, lay down just one inch, then lay the cloth, then lay down another inch. Then add stone little by little to backfill with, working the stone around the outside of the cloth with some stone between the cloth and the pipe all the way around the pipe.

Usually you don't have much vertical working room in the trench to put down the layer of gravel and also get a good pitch for the pipe. The system will still work with perhaps 1/4 inch pitch in five feet of run instead of the normal 1/4 inch pitch in one foot.

Do not dig below the foundation footing bottom close to the footing. For each inch below the foundation bottom you need to dig, you have to be three inches away for example to dig the trench bottom 6 inches below the footing bottom, the entire trench has to be at least 18 inches in from the side of the footing (not on centers).


Do you get coverage you can count on? From the bag of fertilizer? From your lawn sprinklers?

Last edited by AllanJ; 04-23-2011 at 04:18 PM.
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Old 04-23-2011, 06:37 PM   #3
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indoor french drain

If you are using clear, washed, one size stone, put down a layer of filter fabric to slow the water velocity and decrease the amount of silt and clay that will eventually plug the stone. The same applies to the sides.

If you use the tradition mix of clean concrete sand and 3/8 to 3/4" rock, it is not as critical.

The french drains that were installed decades ago on golf courses and are still functioning used a similar fill since the fabric was not available and they were installed without perforated pipe that was not available then.

My first house built is 1917 used 12" long sections of 4" clay tile (not perforated) with loose joints and the same mixture as a filter around the pipe on both the inside and exterior drain tile systems.

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