Unchecked rain water drains to the nearest low spot in the terrain, often under a house and into its foundation, basement or crawlspace. Methods of preventing the flow depend on where the water is coming from. Runoff from the roof can be diverted with a gutter system that includes downspouts, which route water away from the house. Natural runoff from an incline must be intercepted with a subterranean drainage system called a French drain.
Determine the path for the French drain. The drain should lie between the house and the incline, within 2 yards of the house foundation, and angle toward a low point in the terrain. The path does not need to match the exact shape of the house.
Mark the path for the drain, painting in a relatively straight line along the route. Use marking paint that dissolves in water and does not harm plants.
Dig the ditch to a width of 6 inches and a depth of 2 feet. Increase the width to 12 inches in areas subject to heavy rainfall. The ditch should slope downward .1 foot for every 100 feet.
Place landscape fabric along the base of the ditch, extending the fabric up and over the sides by several inches. Start the fabric at the highest point and work toward the endpoint of the ditch. Overlap seams by 12 inches. Then pour 2 inches of gravel over the cloth.
Lay perforated pipe along the length of the ditch, with the holes pointed downward. Do not cap the ends of the drain pipe.
Backfill the ditch with gravel to within 2 or 3 inches of the surface. Fold the landscape fabric over the gravel and backfill the remainder of the ditch with dirt.
Extend the downspouts of nearby gutters to lie near the French drain so that you can siphon off water from heavy rainstorms.