Residential Foundation Drainage Design

Landscaping and Foundation

• 1

  Design a slope, or grade, of the yard so that the ground is higher near the foundation than the rest of the yard. For every 50 feet of yard, it should drop at least 12 inches from the height at the foundation. Ideally, the water is funneled so that it drains into the sewer system and not the neighbor's yard. Take into account play areas, vegetable gardens, large outbuildings such as sheds and garages, and trees that might eventually have roots that rise above the ground and block the flow of water. Each must be on a slightly higher area so the water flows around them instead of directly into them.

• 2

  Plan the foundation so that any wall with usable space on one side and earth on the other is waterproofed.

• 3

  Check in advance with the landscaping contractor just where the soil level is on the foundation so that the unsightly waterproofing rises no higher than it has to. Mark a line with durable chalk across the foundation just where the waterproofing is to go.

Exterior Drainage Design

• 4

  Examine the type of soil you have around the house. Light, sandy soil self-drains to a great degree, and any exterior drainage can be correspondingly light. Heavy clay soil holds water for a much longer time and needs a drain that provides a steady flow away from the foundation.

• 5

  Prepare the bottom of the foundation by planning a several-inch layer of large gravel in a 6-inch-wide trench. Lay a perforated drain tile in the trench and cover it with a sleeve to prevent loose material from entering.

• 6

  Plan to lay more gravel over the tile and then fill the trench with dirt. The end of the tile should extend in the same direction the yard slopes, with a 3-inch drop in height for every 10 feet the pipe runs from the house.

Interior Drainage Design

• 7

  Install a French drain in much the same way that it was installed outside. Plan a gap of about a foot between the foundation walls and floor for the pipe. Place gravel in the gap near the foundation bottom and place the pipe around the interior of the foundation.

• 8

  Cover the pipe with gravel in the same manner as outside. Options include bringing the gravel up to the level of the floor, leaving a permanent gap, or covering the gravel with concrete, making the floor solid from wall to wall. If you cover the drain with concrete, understand that if it ever clogs or breaks, you will have to jackhammer the floor open to access it.

• 9

  Drain the tile to a sump well that is installed along the inside of an exterior foundation wall. The water in the sump is kept low by a special underwater pump that forces the water out through draining pipes and into the sewer.