How do I install French drains?
Dig a trench along the wall or foundation with water issues, making sure that the trench is graded so that gravity will run the water to the proper location. The trench should be no less than 12” wide and the depth just below the bottom of the foundation, footing or wall. Once the trench has been dug, line it with Mirafi 140N filter fabric. Mirafi will allow the water to run into the trench but keep sediment from clogging your French drain system, allow enough fabric to fold back across the top of the trench once the drain rock has been installed. After lining the trench with Mirafi, fill the trench with 2”-3” of ¾” Crushed Drain Rock. Install perforated drain pipe, holes facing down, maintaining a slope so that the water will be carried off by the drain pipe. Fill the rest of the trench with ¾” Crushed Drain Rock, folding the extra flap of Mirafi over the top of the trench. You can cover the top of the trench with soil, sod, mulch or decorative gravel. At the end of the French drain you can connect non perforated drain pipe to run the water into a drain or sump. A typical sump is a 3’x3’x3’ pit, lined with Mirafi and filled with ¾” Crushed Drain Rock. The sump will allow the drain water to percolate into the soil.