When waterproofing your basement there are a few varieties of drainage system to consider. The single most effective solution to basement water is an exterior drain tile system. An exterior system uses a membrane to seal the wall from moisture from the outside, and directs water to a drainage field and sump system to pump water away from the foundation walls. Though very effective at controlling basement water, an exterior drainage system is very costly, and requires major excavation around the entire foundation–which for most homes means that shrubs, gardens, and other landscaping have to be removed prior to excavation, and reinstalled after the system is installed. For most homeowners, the high cost and major disruption of an exterior system outweigh the benefits.
There are also interior drainage systems. Some homeowners choose to install a drainage channel above the concrete slab in their basement. This is the simplest and least costly type of drainage system, and may be effective for poured concrete walls where cracking is the main point of entry for water. However, this does not solve the problem in block walls because water will continue to pool in the block cores. The water level cannot drop below the level of the slab. Also, there is still the potential for efflorescence or mold and mildew on the walls themselves.
Another type of interior drainage system places a drainage channel in the edge of the slab, on top of the footing. Holes are drilled in the base of the block, and the water is moved to a sump basin through the drainage channel. These systems facilitate block drainage, which makes them an improvement on an above-slab channel. However, this system is still less than ideal. Because the blocks are below the level of the slab they tend to sit in water which allows them to become damp. The small drainage channels can be overtaken by water flow during extreme rains, leading to more leaking, and many of these systems leave an open gap between the floor and wall, allowing damp smells and uninvited guests into the house.
The most effective interior drainage system is a sub-slab rigid drain tile system. By placing the drain tile along side the footing, water is allowed to drain to a level beneath the slab. Like the smaller drainage channel system, holes are drilled in the bottom course of the block wall, allowing water in the block to exit into the drain tile. Getting the water across the footing and into the main drainage field is one of the biggest challenges to installing one of these systems. In the past, contractors have used several methods to move water across the footing. Some installed small tubes from the block to the drainage field. These are prone to sediment blockage, and also make it hard to replace the concrete floor to the same thickness as the original slab. Other contractors installed washed rock on top of the footing, which isn’t prone to blockage, but again doesn’t allow the contractor to replace the concrete to the original thickness. Dimpled sheeting is another option which seems to offer the best compromise between water flow and concrete integrity. It allows unrestricted flow AND allows for concrete replacement at the original thickness but here, again, leaves an open gap between the floor and wall.
Of course, you should consult with a professional to find out if a drain tile system will fit your needs. Standard Water’s experienced staff can give your home a professional evaluation and help you make the right decision for your home.
for more information: http://www.standardwater.com