How to Install a Interior Perimeter Drain System

Excavation

• To do an effective drainage job, an interior perimeter drain must be lower than the concrete slab that floors your basement. That means your first step is to break up around 12 inches of concrete around the entire basement wall and dig a trench next to the footing that’s deep enough to put the drain below the bottom of your slab floor. If you don’t have an existing sump pit and pump to drain the water into, you will have to dig a hole to install a sump pit and pump. If you are on a hillside, you can use gravity to drain the water downslope. If doing the job yourself, you'll need helpers to haul the broken concrete and dirt up from the basement for disposal and to bring down the materials for the French drain.

Lay Tile

• Line the perimeter trench with porous non-deteriorating landscaping fabric and pour around 3 inches of washed pea gravel across the bottom of the trench. Enclose 4 inch perforated PVC plastic drain tile in a spun filter sock and lay it on the gravel with the rows of holes facing down at the 5 o’clock and 7 o’clock positions. If possible, slope the drain tile slightly downward toward your sump. If sloping is impossible, lay the tile level. Cover the drain tile with coarse gravel or crushed rock and top the stone with more porous landscaping fabric.

Walls & Sump

• Lay a commercial dimple board along the base of the wall and on top of the stone before pouring the new concrete. The dimple board creates a space next to the well that will allow moisture seeping in through walls to drain down into the French drain. Line your sump pit with a commercial sump liner and install a good-quality sump pump that takes the water outside and away from the foundation. If you are concerned about power failures, you can install a secondary battery-powered backup sump pump.

Drain Cost

• You can expect to spend between $2,000 and $6,000 to have a contractor install an interior basement perimeter drain. If you need to install a sump pit and pump, your cost could double. Most of the cost is labor. If you decide to do the job yourself, the materials are available and affordable at most hardware and home centers. Before you start the job, make sure there are no utilities under your basement floor. Your local community may require a construction permit and have the work inspected. If you plan to use a contractor, get multiple estimates and make sure the company is bonded and insured.