How to extend gutter downspouts underground for drainage

Written by emily patterson
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Gutter downspouts can be located very close to a house and cause problems with water seeping in the foundation wall or cause dampness in a basement. Underground drainage for downspouts can often solve this problem. When installing underground drainage for downspouts, locate an area that is lower than the house to drain the water. Be careful that you aren't directing water onto the property of a neighbour in an area that can cause them problems, such as close to their garage, driveway or house.

Skill level:
Moderate

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Things you need

  • Shovel
  • Garden rake
  • String
  • Line level
  • 2 stakes
  • Landscaping fabric
  • Crushed stone
  • 4 inch perforated pipe (solid pipe may be used)
  • 4 inch downspout adaptor
  • 4 inch grate
  • Downspout section
  • Tape measure
  • Hacksaw
  • Drill
  • 1/8 inch drill bit
  • Screwdriver drill bit
  • Sheet metal screws

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Instructions

  1. 1

    Dig a two feet deep, two feet wide, trench that slopes downward one inch for every one foot from the location of the base of the downspout to an area that can absorb the water or is far enough below the level of the downspout that the pipe can expel the rainwater. Dig the sod out in pieces and lay to the side to replace later.

  2. 2

    Tie a string around a stake at the beginning of the trench at ground level. Tie the other end to another stake at the end of the trench. Use a line level to level the string. Calculate the grade by measuring the distance of the string. For each foot, lower the string on the drainage end of the trench by one inch. Finish digging the trench to two feet below the string the entire length of the trench.

  3. 3

    Lay landscaping fabric in the trench the entire length of the trench.

  4. 4

    Pour 2 inches of crushed stone into the bottom of the trench. Use the string to ensure that the stone is 22 inches below the string the entire length of the trench. Use a garden rake to level the stone.

  5. 5

    Lay perforated pipe into the trench. The pipe must be long enough to start at the downspout and reach the end of the trench. Use the string to ensure that the top of the pipe is 18 inches below the string the entire length of the pipe. Remove the string and stakes.

  6. 6

    Install downspout adaptor on the opening of the perforated pipe where it will attach to the gutter.

  7. 7

    Install a grate adaptor on the opening of the perforated pipe on the end where it will drain to prevent animals from entering the pipe.

  8. 8

    Install a leaf strainer in the gutter at the opening of the downspout to prevent leaves from entering the downspout. The leaves can plug the drainage pipe.

  9. 9

    Add a section of downspout to the existing downspout so it extends into the downspout adaptor attached to the perforated pipe. Use a hacksaw to cut the downspout so it is easier to attach the extension piece.

  10. 10

    Measure the distance between the end of the downspout and the entrance to the downspout adaptor. Add two inches Use a hacksaw to cut a piece of downspout using this measurement.

  11. 11

    Push the extension piece over the existing downspout and insert the other end into the downspout adaptor on the perforated pipe. Pre-drill pilot holes in the existing downspout and extension piece. Use sheet metal screws to attach the section of downspout to the existing downspout. The end in the drainage pipe does not have to be secured.

  12. 12

    Pour two inches of crushed stone over the perforated pipe. Lay landscaping fabric over the top of the stone and trim excess.

  13. 13

    Replace enough of the soil so the retained sod can lay on top level with the existing ground surface. Tamp the soil and lay the sod pieces on top of the soil. Water the sod after replacing.

Tips and warnings

  • Keep the replaced sod moist to encourage growth. Keep the gutters clean to prevent leaves from accumulating in the pipe. Clean the drainage pipe annually with a plumbers snake and water from a garden hose to reduce the risk of the drainage pipe becoming plugged with soil or other debris. Tree roots and roots from shrubs or other plants may block the pipe. Be sure to monitor roots that may grow near the drainage pipe.
  • Check with your local utility companies for underground utilities before digging to prevent the risk of serious injuries or expensive damage to utilities.

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