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French drain question on a small flat lot in high desert Idaho

John_Brown | Posted in General Questions on


I have a question regarding how I should approach the French drain I will need for a small house (basement) and the adjoining shop (crawlspace). The lot is 80′ x 100′ and is basically flat. It is not in the floodplain. I spoke with the local building inspector and he said that folks do install French drains so I want to have a strategy. I am curious to hear how a pro might approach this problem. Could I dig out a large cavity during excavation (and fill with aggregate) as a basin towards which I could direct the pipe? It’s pretty arid here (but there is snowpack and runoff).

I will post a diagram later showing how a diversion strategy.

I’m basically confused as to how to deal with the different elevations of the footings and how to slope the pipe given there isn’t much grade to work with. About how far away from each structure is a safe distance to have an exit?

For site data, there is about 16 inches of annual rainfall (precipitation) according to my research.

Thanks in advance.

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  1. user-2310254 | | #1

    You could install a perimeter drain system and connect it to a sump located in the basement. Have you checked with any future neighbors to see if any have drains and/or basement water issues?

  2. GBA Editor
    Martin Holladay | | #2

    The approach you describe is called a drywell. The drywell should be as far from the house as the size of the lot allows, up to about 60 or 70 feet away.

    If you can't install a drywell, or don't want to install a drywell, the other option (as Steve Knapp noted) is to install a sump in the basement. The sump pump can discharge any water that collects in the sump to the surface (far from the house) or, if permitted by local authorities, to the town's storm drainage system or sewer system.

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