How to Add a Drain to Your Garage

Written by jeff nemes
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Having a drain in a garage is important if you park your car in the garage and live in a place where there is a lot of precipitation the car may carry into the garage. If installed when the garage floor is poured, it is a simple project. Putting a drain in after the floor is poured is not difficult, but it is labour intensive. Drains installed after the slab is poured may not be highly functional, as the slab is generally poured level, rather than with a slight slope into the drain.

Skill level:

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Things you need

  • Concrete cutter (or circular saw with a concrete cutting blade)
  • Jack hammer.
  • Reciprocating saw with metal cutting blade
  • Hearing protection
  • Floor drain
  • 2-inch PVC or ABS pipe and fittings
  • Exterior drain box
  • 1 to 2 wheelbarrows full of washed river rock
  • Concrete mixer and concrete mix

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    Prepare the Floor

  1. 1

    Determine and mark where you want the drain and where the pipe will run through the floor and outside. Carefully mark the floor using a chalk line, marker or paint.

  2. 2

    Score the concrete using the concrete cutter so you will have a straight line.

  3. 3

    Break out the concrete using the jack hammer, cutting rebar with the reciprocating saw. Haul broken concrete out of the garage.

  4. 4

    Dig a trench for the pipe, saving the gravel you dig out. The pipe needs to drop 1/4 inch per foot to drain properly.

  5. 5

    Dig a hole outside into which the water will drain. Install the drain box.

    Install the Drain

  1. 1

    Run the pipe in the ditch, carefully gluing its joints. Install the drain and use rocks or gravel to hold the drain in place just below the level of the garage floor, which allows the water to run down into the drain. The pipe should exit into the drain box outside. Note: Some people simply dig a deep hole in the garage, place river rock and a grate or drain, and allow the water to drain into the hole in the garage. This is not recommended as it deposits water under the garage slab and can cause cracking, shifting and other problems, especially in areas with freezing temperatures or poor draining soils.

  2. 2

    Test by pouring water into the drain to verify that it is running down the pipe and out the drain box.

  3. 3

    Cover the pipe with the saved gravel. Leave space for 4 to 6 inches of concrete.

  4. 4

    Mix concrete and pour into the ditch, carefully smoothing the concrete to be level with the floor and around the drain. Time and patience will produce a much smoother finished product. Carefully clean any spills or residue, then allow the concrete to cure.

  5. 5

    Treat the floor with a concrete floor sealer to keep water from running into the seams.

  6. 6

    Fill the drain box with river rock and cover.

Tips and warnings

  • Depending on how far you run the drain pipe, it may prudent to order premixed concrete delivered in a truck.
  • Carefully check local codes about drain water and garage drain filtering requirements. Large urban areas tend to have particularly strict codes relating to garage drains, and may require special filters, tying the drain into local sewer systems, or may not allow a garage drain at all.
  • Also check with your local government for requirements and to obtain any necessary permits for remodelling projects.
  • Always check for wires and cables before digging the outside trench for the drain line.

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