How to Replace an Underground Downspout

Replacing an underground downspout can protect your house and yard from water damage. Plastic downspouts frequently get crushed under the soil and need replacing. Leaking water from downspout joints above ground or standing water where the downspout heads underground are two symptoms of a damaged underground downspout.

Standing water can harbor mosquitos.
  1. Dig up the downspout, starting at the point where it enters the ground. Remove the downspout, clear debris from it and replace it into the original spot if the pipe is not compromised. Cover it with gravel and refill the trench with the surface dirt that you removed when digging up the downspout.

  2. Obtain a replacement pipe if needed. Buy a new pipe that meets the U.S. Department of Agriculture recommendations (an underground downspout must have a greater capacity than the gutter downspout that drains into it). Additionally, the Department of Agriculture states that the underground downspout should be rated for this underground use, and should be composed of durable materials and have a 10-year life expectancy.

  3. Evaluate the drainage ditch from which the underground downspout has been removed. The downspout bed should drain into an area where water would naturally flow downhill, away from structures and into an area that will absorb the runoff such as a lawn or garden.

  4. Repair any errors in the existing lie of the downspout bed. If needed, dig a new trench to fix existing problems. Dig the trench deep enough to accommodate 2 inches of gravel, the width of the pipe, 2 inches of gravel and 2 inches of soil to be level with the surrounding surface when complete.

  5. Replace the underground downspout. Line the downspout bed with at least 2 inches of gravel, place the downspout into the trench, test it with the garden hose and then reconnect the new downspout to the gutter downspout. Cover the downspout with at least 2 inches of gravel and cover it with soil.


  • Underground downspouts should gradually be on a descending grade and point away from structures.
  • Underground downspout turns should be at angles at less than 45 degree.
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