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Thread: French Drains & Down Spouts

  1. #1
    Electrical Engineer jdf405's Avatar
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    Default French Drains & Down Spouts

    I recently had gutters & down spouts installed on my house (in Los Angeles) and I'd like to get the water a bit further from the house than simple splash blocks. I live fairly close to the beach and get epic fog & dew most of the year, so the ground around down spout is wet 75% of the time.

    I started reading about piping the down spouts under ground to what I thought were French drains. Then I read that French drains were for taking water from in the ground away, not for allowing water from a down spout to soak into the ground.

    I'm confused - are French drains good for both purposes? Or is there a better option for my down spouts? Piping the water all the way to the curb isn't easy on my property and the city is very strict about cutting the curb to install a drain.

    Thanks!
    Jonathan

  2. #2

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    In a typical installation french drains are placed around the outside perimeter of a footing of a house to (try to) keep water out of the basement. Obviously this is much easier to do when building the house than after the fact, but it is done both ways. French drains drain to daylight if you are lucky and are on a slope otherwise the drain to a dry well. NEVER connect downspouts from the roof to your french drains. People have done this - it turns out badly unless your intention was to have an indoor swimming pool in your basement.

    What you want is to build a dry well to drain your roof gutters into. A dry well is essentially a large hole in the ground filled with crushed stone, with some sort of plastic mesh on the sides and on top to keep the dirt out. You pipe your drain pipes over to the dry well and the water will leach out into the surrounding soil below the surface and out of sight. They can work - or not - depending on the soil type (sand is best) and how much water they are expected to handle. Also if you have a basement keep them away from the house or the water will find its way in!

    -rick

  3. #3
    In the Trades Gary Swart's Avatar
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    Hate to admit it, but I installed French drains for the sole purpose of giving my downspouts a place to go. It's been 5 years or so, not a drop of water in the basement. The soil at the level I trenched to is quite rocky, so there seems to be excellent drainage. Maybe I screwed up, but I seem to be getting away with it!

  4. #4
    DIY Senior Member Nate R's Avatar
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    I think Rick is only looking at it in the sense of hooking downspouts to existing footing drains.

    French drains that one installs (By french drains I mean french drains. Not referring solely to french drains used around footers) can be used for both dispersing water and removing it. In the times you want to remove it, the soil will be pretty wet and water would easily build up in the pipe. When you want to disperse it from the pipe, you usually do it in soil that isn't saturated w/ water.

    For getting rid of downspout water, I'd dig a trench, line it w/ geotextile fabric and lay the slotted pipe in a gravel bed. Then surround it all with more gravel and topsoil on top to grow grass on. (Fabric between topsoil and gravel below) Then, at the end of the trench, I'd put in either a prefab drywell or make my own.
    http://www.thenaturalhome.com/drywellinstallation.htm

    The trenched area would take the initial water from the gutter. As the soil around it started draining slower during a storm, water would then go to the drywell to be temporarily stored and dispersed over more time. As was said, your soil needs to drain well enough for this. Might be worth digging a hole and doing a simple perc test first.
    Last edited by Nate R; 01-10-2009 at 11:02 AM.

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