An Overview of Solutions to
Basement Moisture Problems

APPROACH 1:
Install Proper Gutters and Downspouts and Correct Grading

A great number of basement water problems can be solved by handling rainwater and surface drainage properly using gutters and downspouts with extenders or splashblocks to carry the water away from the foundation. Sloping the grade away from the house, which may require hauling fill to the site, is very important. This should be done before any below-grade drainage system is installed, since the above-grade corrections may solve the problem. Even if a drainage system is required, removing water at the source as much as possible is necessary.

APPROACH 2:
Exterior Drainage System

Installing an exterior drainage system at an existing building is the most costly, but also the most effective water control approach. This requires digging up the area around the foundation and rebuilding it similar to a new house installation. It also requires digging up shrubs and other obstacles around the house.

Usually, waterproofing and insulation are installed at the same time, in addition to making any repairs to the structure. The traditional exterior drainage systems use free-draining sand in the backfill. Drain tile can be placed beside or on top of the footing. Level drain pipe installations are satisfactory. A minimum of 12 inches of coarse aggregate should be placed around the drain tile.

Free-draining Membrane or Board

It can be expensive to haul pea rock or sand to a site for backfilling purposes. Instead, a drainage mat can be placed against the foundation wall and then backfilled with any soil on site. The drainage must have a free-flowing path to the perforated drain pipe below.

Draining to a Sump
All exterior drainage systems must drain to a sump that can be pumped out. The sump must have an airtight, childproof cover.

APPROACH 3:
Interior Drainage Channel above the Concrete Slab

In most cases when water is entering the basement, an interior drainage system is installed. The simplest and least costly approach is a drainage channel adhered at the base of the wall and the floor slab. Water is collected and drained into a sump using another channel placed on top of the slab, then through a trap to the sump basin. The sump should have an airtight, childproof cover. This system is best suited to a concrete wall with cracks. It does not solve the problem in masonry walls because water remains in the block cores at floor level and the water level is only lowered to the top of the slab. With this approach, the water is not completely removed from the space. The result is that humidity, mold, and mildew can still be a problem. This system cannot drain groundwater from under the floor slab.

APPROACH 4:
Interior Drainage Channel within the Slab Edge

Another technique is to place a drainage channel at the base of the wall on top of the footing. This requires removing and then replacing the concrete along the slab edge. The drainage channel is connected to a drain pipe leading to the sump. The sump should have an airtight, childproof cover. This approach is effective for concrete masonry walls with water problems because it drains the block cores completely. Holes must be drilled at the base of every block core to permit drainage. This may require removing more than the minimum amount of concrete, as shown, to fit the drill in. These systems have different shapes and prices depending on the product installed. Because moisture is allowed to penetrate the block cores, it is essential to cap the tops and place a vapor-retarder coating on the interior basement walls.

APPROACH 5:
Interior Drainage System Beneath the Slab

The most effective of the interior drainage systems is a perforated drain pipe installed inside the perimeter of the footing. This requires removing and replacing concrete at the slab edge. By placing the drain pipe beneath the slab, it drains the area to a lower level. Similar to an exterior system, the drainage pipe connects to a sump. The sump should have an airtight, childproof cover. A critical component of this approach is the dimpled plastic sheeting placed at the base of the wall and beneath the slab edge. Dimpled sheeting is similar to a small egg crate and permits free drainage of the wall into the drain pipe. It is less expensive than many specialized drainage channel systems. In low permeability soils, this system cannot accept rising groundwater unless there is an aggregate layer under the slab.

It is recommended that this approach be combined with an active soil gas management system that connects with the sump and perimeter drain pipe.