Paver Patio project - Drainage question (pics)

Discussion in 'Hardscaping' started by f.bennett, Nov 20, 2018.

  1. f.bennett

    f.bennett LawnSite Member
    Messages: 2

    I'm in the process of prepping for a paver patio with a retaining wall. I've excavated to at least 9" deep. My concern is the drainage. As you can see, I have clay soil and the patio is surrounded by mostly higher ground. Do you think it's necessary to install a french drain in this pit? I have two options for diverting the water, but I'd like to get feedback on how you might handle this job. I'd really appreciate everyone's input. Please pardon the mess!

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  2. Delmarva Keith

    Delmarva Keith LawnSite Senior Member
    Messages: 524

    I’d recommend installing a drainage system under this pit. Looking at the surrounding landscape, I’m guessing it’s in a place that freezes over Winter. The water table should be kept below the gravel base of the hardscape if that’s possible. Can you run french drains to daylight somewhere or is this the low spot of the whole lot?
     
  3. f.bennett

    f.bennett LawnSite Member
    Messages: 2

    You are correct, it does freeze. I'm in zone 7 climate. I would have to run about 30 feet of pipe before it hits daylight where the slope would be lower than the pit. Where would you place the french drains in the pit? Thank you very much for your reply!
     
  4. TPendagast

    TPendagast LawnSite Fanatic
    Male
    Messages: 14,894

    I’d make a raised patio
    It don’t make the patio at the bottom of your retaining wall, make it at the top.
    Steps up from the concrete area
    It think it would be better and feel roomier rather than enclosed.
     
  5. zedosix

    zedosix LawnSite Silver Member
    Messages: 2,682

    First thing I would do assuming my project is to remove the concrete slab. It looks to be sitting a bit low anyway, at least then you can work with all the same stone without making it look like patchwork.This way you will be sitting approx. 4-6" higher than you currently are and hopefully drainage won't be such an issue.
    Just random thoughts as I look at the landscape....
     
  6. Delmarva Keith

    Delmarva Keith LawnSite Senior Member
    Messages: 524

    The distance between drains “should” be roughly 2 x 1.4 x depth. I don’t think anyone actually places them that close. Trench a french drain or two in the pit and add an inch or two of gravel. Then lay the pipes and cover the whole pit with your gravel base, then sand or however you plan to set the pavers. The water table will stay no higher than the level of the drains. Depending on surrounding slope, you may need surface drains too.
     
  7. AGLA

    AGLA LawnSite Bronze Member
    Messages: 1,804

    The biggest potential issue looks to be water draining into the patio more so than draining the patio. It would be best to divert surface water around the new patio and deal with the runoff of the patio itself as a separate issue. You'll want to have your retaining walls higher than the existing adjacent grade so that your finished grade pitches back toward the slope to make a swale diverting some of the water coming down that slope into your backyard and some of it to your side yard.
    Hopefully that water can continue toward the white minivan without puddling in your back yard and out toward the street on the other side without finding its way onto your patio.
    Then make sure to pitch your patio so that you can collect that water along one edge in a 4" wide gravel filled trench with a perforated pipe going into a drywell or to daylight if your front yard is lower.
     
  8. visionscapes35

    visionscapes35 LawnSite Member
    Messages: 6

    A french-drain is used to capture and divert SUB-SURFACE water, meaning the water is coming from the ground, rising towards the surface. You are describing a surface water problem.
    I would follow Tpendegast and elevate the patio above the poured slab.
    if not, create a few swales to divert surface water, along with some surface drains throughout the patio itself and along the low side of patio.
     
  9. Delmarva Keith

    Delmarva Keith LawnSite Senior Member
    Messages: 524

    We must be looking at different pictures. What i see is a permeable layer (gravel base, sand, pavers) to be installed deeper than surrounding impermeable clay. Functionally a shallow swimming pool. When the water trapped in that pool freezes, the pavers will heave. Must provide for subsurface drainage.
     

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