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Paver patio drainage

Discussion in 'Landscape Architecture and Design' started by PowerPlay, Feb 5, 2004.

  1. PowerPlay

    PowerPlay LawnSite Member
    Posts: 39

    All right guys, this is my first post and I hope you can help me with a certain job right now. I have a couple questions about paver patios. This is one of my first projects of this type and size. I am installing a paver patio roughly 500 ft2 and a stacked stone wall 50'Lx2'Wx3'H. Excavated the area, compacted the soil, filled with 6" drainage gravel, then 1-2" granite dust. I sloped the surface grade in the general direction that I want the water to move. I am worried about a few pockets where water may accumulate under gravel (I'm not convinced that the grade is exactly right). The main question is, does the majority of the water on a paver patio move across the top of the brick surface, or does it get in the joints between the bricks that are filled with granite dust and move to ground level. It has been very wet lately in my area and I am having trouble laying the brick because of frozen ground in the morning and/or concerns about it being too wet. Also in general, will a patio settle if the subsurface gets wet during construction. Soils on this job are clay and water barely moves through them. Thanks for all the great information on this site.
  2. pjslawncare/landscap

    pjslawncare/landscap LawnSite Bronze Member
    Posts: 1,410

    I am not an old pro, but I have put in a few paver patios. Im sure someone here will answer you as well, but Ill give it a try. I beleive most of the water will run across the top surface as long as you slope it at least 1/4" per foot. Some will go between pavers though, but minimal. If your worried about pockets in your grade, use stakes and string to verify smoothness if you havent already done so. I also believe it is good to water down subsurface a bit as it helps stabelize and compact things. It shouldnt settle much at all if you compacted subsurface properly. Like I said Im not an old pro so I hope other will give their input as well. My patio is still holding up nicely after 3 years now.

    back patio.jpg
  3. bcx400

    bcx400 LawnSite Member
    from PA
    Posts: 77

    The amount of water that passes through the paver joints is determined by 1.) the size of the joints (some of the tumbled pavers have wider joints than non-tumbled pavers, which usually have 1/16" joint 2.) the pitch of the patio- as the last post states, a pitch of 1/4" per foot will ensure good runoff 3.) the age of the patio- over time the pavers 'lock-up' and less water will pass through, if you keep adding joint sand when necessary.

    The sub-grade should always reflect the pitch of the patio (1/4" per foot). Water that does perk through the paver joints will puddle, especially with a clay-based subsoil, unless the subgrade is pitched properly. Any soft soil (especially clay soils) should be removed prior to installation of your gravel base. I usually excavate to an 8" depth- but if the subsoil is clay/wet and 'pumps' when you walk on it, then keep digging until you hit a soild base. I have dug patios 24" deep in spots to get to a hard base. Obviously, you need to charge more for this.

    As for installing pavers in freezing temps- don't do it. If your subsoil or gravel base freezes, your final elevations will be off from heaving.

    ALWAYS use a geo-textile fabric between the subsoil and gravel base. This is especially helpful with clay-based subsoils. The fabric will help prevent the gravel from migrating into the subsoil, which could cause the pavers to settle.

    Always use concrete sand to set your pavers on. Screenings continue to break-down into smaller particles over time, and do not vibrate up into the paver joints as well as sand when compacting the pavers.
  4. bcx400

    bcx400 LawnSite Member
    from PA
    Posts: 77

    This is a must visit site for paver installers www.icpi.org
  5. PowerPlay

    PowerPlay LawnSite Member
    Posts: 39

    Thanks for the info guys. That patio looks terrific PJS! The ICPI website sums it all up. I know I made a couple mistakes on this project but the customers actually want a "rough" look. So I will probably get away with it. They had some brick pavers in there before which were totally uneven in my opinion and it didn't seem to bother them much. I know it will be a huge improvement over that. I have another paver project lined up after this one and now I know how to do everything correctly! Thanks.
  6. AGLA

    AGLA LawnSite Bronze Member
    Posts: 1,742

    A paver patio is considered, by engineers, to be an impervious surface. When they caculate runoff it is usually 100% of the rainfall that is expected to runoff. I have seen some calculations where they used 95%. Either way, don't expect drainage through the joints.

    I work in a civil office and often have to do these calculations.
  7. PowerPlay

    PowerPlay LawnSite Member
    Posts: 39


    So typically no water will move in even if we are talking about .125" - .25" spacing between brick joints as long as they are filled with sand and the patio has a finished pitch? Also another question, if water does not move into the joints and then to the subsoil level, then the subsoil grade is not all that important as long as it roughly moves away from the house to account for a worse case scenario rain? There seems to be a lot of concern about the subsoil grade, but if the water is never going to get down there, then maybe it isn't all that big of a deal?
  8. bcx400

    bcx400 LawnSite Member
    from PA
    Posts: 77

    Powerplay- water WILL pass through paver joints. Just because it is considered an impervious surface, doesn't mean water will not penetrate through the joints. Larger paver joints will enable more water to pass through. Next time it rains, watch what happens to your patio. During a light rain, almost all of the water will pass through the paver joints. During a heavy rain, most of the water will run off. This is true of most pervious surfaces as well.

    A gravel driveway is considered an impervious surface here in PA- yet water passes through the layers to the subsoil.

    The preparation to a paver patio is the key to a long lasting finished surface. Don't skimp on base prep.
  9. matthew horner

    matthew horner LawnSite Senior Member
    Posts: 696

    I work in Raleigh also. Howd the job go?
  10. PowerPlay

    PowerPlay LawnSite Member
    Posts: 39


    Project turned out great. Customers are very happy. Most of my experience is on the golf course and with plants. Learned a lot about hardscaping on this one and I feel that I finally got everything correct with the help from people on this board. Already got another one lined up down the street. Where do you do most of your work at in Raleigh?

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