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How to Prevent Erosion Under a Deck

A deck provides a decorative and functional outdoor lounging area, but it can also cause erosion problems in your yard. As water runs off your deck or through the deck slabs, the impact of the falling water and the resulting runoff can erode the soil under the deck. This can cause the supports of the deck to become unstable. There are steps you can take to prevent erosion of the stabilizing soil under your deck.

If your deck is high, grass will continue to grow underneath the deck.
  1. Keep the sod and grass in place under your deck. Higher decks will allow enough sunlight to pass underneath to keep the grass alive. The grass will hold the sod in place, preventing erosion.

  2. Dig small drainage trenches in the spots under the deck that are most prone to erosion, such as areas between boards or along the edges of the deck where runoff can occur. Start the trenches at 8 to 10 inches deep, and then make them 1 inch deeper for every 10 feet of trench you dig. Stop the trench at least 10 feet away from the deck.

  3. Dig a small hole at the end of each trench that is at least 1 foot deeper than the trench itself. Fill the hole with rocks. Line the bottom of the trenches with 1 inch of gravel, and then lay a perforated PVC pipe on top of the gravel. Fill the trenches the rest of the way with gravel. Water from runoff will land in the trenches, and the PVC piping will direct it to your rock well, preventing erosion of the sod.

  4. Cut a sheet of landscaping fabric to fit under the deck, and then lay it flat over the sod and your trenches. Cut away the portion of the fabric that covers your trenches. Cover the rest of the landscaping fabric with a 6-inch layer of gravel.

  5. Install a lattice skirt around your decking that reaches from the bottom of the deck to the ground. If wind is causing erosion under your deck, the skirt will block some of the wind.

  6. Plant decorative shrubs along the lattice skirt to provide further wind blockage. The shrubs will also help keep the sod together. Plant shrubs that are appropriate for your climate and soil type.