Where the buildings are built right to the property line, it is impossible to install a traditional drainage system on the outside of the foundation.  We must install a system on the interior.  Unfortunately, that usually requires removing the slab and replacing it.  Usually, interior improvements must be removed as well.  Once the slab is gone the ground is excavated to a depth of 8” below finish floor.  Two trenches are then excavated, each one quarter of the way across the house and running the length of the house.  These trenches are then tapered to create swales that also slope toward the drain point.  Into each of these swales a perforated drain pipe is installed and connected together to exit the building.  I always wrap these pipes in filter fabric to keep them from silting up and I install a cleanout at the upper end.  I then install drain rock in the basement and compact it to a level 6” below finished floor.  To prevent any water vapor from intruding I install a Visqueen vapor barrier, covered with 2” of course sand on top to break any capillarity action.  On top of this goes the new reinforced concrete slab.  Since it rests on fill, I always add additional reinforcement to the slab.

It is possible to dispose of the collected water on your property if you have enough land and if it is sloping in the right direction.  However, it is a code violation for any of your water to pass onto your neighbor’s property, and you will be liable if it causes him any damage.  Usually this water is disposed of in the city sewer system.  A concrete sand trap is required to protect that system from any possible silt.  All this is involved and expensive, but it is the only way I know of to guarantee a dry basement.  Indeed, I am one of the few contractors that will offer a dry basement guarantee for seven years.


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  • Molly O'Malley

    At Last I know how to install this marvelous drain! MIcheal I have no idea how I found this and figured out it was you. We are in 14 ” of snow and I have baked my last cookie so I surfed and landed on you. I hope you are happy and well. I am sending my Christmas letters a bit late this year.
    Best wishes always,
    Molly O’Malley

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