Patio Drainage Concern

Discussion in 'Hardscaping' started by cmpbllarg, Feb 26, 2013.

  1. cmpbllarg

    cmpbllarg LawnSite Member
    Messages: 3

    I am in the process of installing a patio on the side of my house. I feel like I have done enough research to feel comfortable with the soil prep, base layer, sand, paver, edging, etc. My concern is drainage.

    The soil where the patio will be is entirely red clay. If I excavate the area and install the gravel baselayer, I feel like I am creating one big bathtub (albeit filled with gravel) that my patio will be placed on top of.

    Do I need to install drainage underneath the patio (i.e., in the baselayer) to alleviate this potential problem?

    Thanks in advance for the advice.
  2. shovelracer

    shovelracer LawnSite Silver Member
    Messages: 2,008

    Your base is impermeable. However, if you felt your clay was poorly draining I could see a drain system in the subgrade to relieve excessive water percentages. This could be beneficial, but more than likely is not necessary. The important part is making sure your subgrade is the right moisture content before you cover it. If it is too wet you'll just turn your patio into one giant trampoline once you run the compactor and those molecules get nice and lubricated.

    The general answer to your question is no, but we do not have pure clay up here either so perhaps some southern guys will be able to provide some more advice.
  3. alldayrj

    alldayrj LawnSite Gold Member
    Messages: 3,793

    geo fabric may also be helpful, as well as proper pitch
  4. zedosix

    zedosix LawnSite Silver Member
    Messages: 2,665

    Make sure your excavated base is sloped to follow the finish grade. Don't create any divits or sunken areas in the excavated area or it will eventually hold ground water and the frost will heave the patio. Also don't forget to excavate beyond the finish perimeter by 12" or so. If you can install a drainpipe at the lower end and have it exit at lower ground then this would benefit.

    Oops as I read back and check the area you are in, it looks like frost is not going to be a concern for you.
  5. cmpbllarg

    cmpbllarg LawnSite Member
    Messages: 3

    Thanks for the feedback. My plan will be to (1) make sure I grade the excavated area to match the patio surface (i.e., 1/4 in. per foot sloping away from the house, (2) install geotextile cloth b/w the clay soil and the gravel baselayer, (3) potentially install a drainage pipe on the low end if I get worried enough about it. And, zedosix, you are correct: if I start having trouble with frost heaving in my area, Al Gore is going to have some 'splaining to do.
  6. DLCO

    DLCO LawnSite Member
    from Ontario
    Messages: 14

    1/4" per foot seems like a large ammount of slope... how large is your patio area going to be? I tend to slope 1" per 10 feet (which on a level would be so the bubble is just a little over the line)
  7. zedosix

    zedosix LawnSite Silver Member
    Messages: 2,665

    That is hardly enough slope. At minimum 1%, ideal would be 2% grade.

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