Drainage and Retaining Walls
- Installing a retaining wall with proper drainage saves you the time and hassle of repairing the wall in the future. Start the wall over a thick, solid bed of 3/4 in gravel so underground moisture can drain away easily. When choosing your material, consider dry-stacking stones or drilling rebar through pressure-treated timbers to allow water to seep through the narrow crevices in the wall.
- Drilling holes through a retaining wall effectively releases water buildup. Space them 2 to 4 feet apart about 6 inches from the bottom of the wall, depending on whether your soil is sandy or clay-like. Fit metal or PVC pipes through the holes so water can escape from behind the wall. In addition to horizontal holes, dig vertical holes through the soil immediately behind the wall. Line the holes with a filter fabric, and fill them with gravel.
- If the soil behind an existing retaining wall feels soft and waterlogged, improving the drainage calls for more drastic measures. Use a flat shovel to dig out a 1-foot wide section of soil from behind the length of the wall. Dig down to the foundation, and line the back of the wall with waterproofing fabric to protect the wall from rot and other damage. Backfill the wall with a mix of equal parts soil and sand so water can more easily penetrate through to the drain holes along the bottom of the wall.
- Lay underground drain pipes in front of the wall to capture water and carry it away to a safe drainage outlet. The pipes should be about a foot from the base of the wall. Dig the trench 18 inches deep and 10 inches wide, and line the bottom with gravel. Use perforated PVC drain pipes to direct water runoff away, and cover the pipes with gravel. Keep the gravel exposed if you like to way it looks, or cover it with a layer of soil and flood-resistant groundcover to conceal it.
