Building a French Drain
Establish the route of the trench. This should be in a U shape, with the bottom of the U opposite to the house and along the highest level of the yard. The arms of the U will slope toward the lowest level of the yard. The arms may extend along the house or stop at the house, but in either case should be at least 4 to 6 feet from the foundation.
Pound in stakes at each corner and end of the projected trench and run a string line. Measure the linear length of your trench to determine the amount of pipe and gravel needed. Gravel is purchased in cubic yards. The trench will be 6 inches wide by 24 inches deep. Figure the amount of gravel needed by multiplying length times width times depth. Keep all units of measurement consistent.
Commence digging along the string line. Thoroughly tamp down the base of the trench. Then fill and level with 1 to 2 inches of gravel.
Lay the perforated pipe with holes facing down. Fill the trench completely with gravel, level with the surface of the yard. Make the French drain not only functional but ornamental by using ornamental rock to fill the final two inches of the trench. This drain will capture surface and ground water to eliminate problematic drainage.
Things You Will Need
- Rounded, washed gravel or ornamental stones
- Perforated pipe (French drain pipe)
- 4 stakes
- String line
- Mallet, or some kind of hammer
- Allowing the lower end of the pipe to extend out onto the level surface of the ground will allow for the best drainage for this particular system. Incorporating the drain into a landscape feature is also decorative yet functional.
- Example for computing cubic yards: For a 40-foot linear trench, multiply 0.5 feet (6 inches) by 2 feet (24 inches) by 40 feet. This equals 40 cubic feet divided by 9 to determine cubic yards. The amount of gravel needed is 4.5 cubic yards---rounded up from 4.44.