I recently received a call from a homeowner who says that, during heavy rains, water enters his basement between the floor and the wall. What are some possible causes of this? How do you correct this?
Leaks between the basement floor and wall are usually the results of inadequate surface drainage or, if present, a poor drain-tile system. If water accumulates next to the structure, it can enter under a hydrostatic head at the location of the isolation joint between the wall foundation and floor. The preformed asphalt-impregnated fiber sheeting usually used to create this type of isolation joint is not an effective water seal. The joint allows the floor to move independently from the wall and foundation. The first line of defense against basement leakage is to drain surface water away from the structure. The second is to collect and drain the underground water away using a drain-tile system. To drain water away from the surface, finished grade should fall off 1/2 to 1 inch per foot for at least 8 to 10 feet from the basement wall. Add fill material to offset reverse drainage caused by settlement or improper grading. On hillside sites, it may be necessary to construct cutoff drains on the uphill side to drain surface water around and away from the basement walls. Inspect downspouts and splash blocks to ensure they divert water at least 3 feet from the structure. Drain-tile systems can be either inside or outside the footing. McCoy recommends evaluating the current system by opening the corners of the basement (for interior systems) or excavating (for exterior systems) to gain access to the drain tile. Then flush the drain tile with water to detect problems. McCoy says plugs, breaks, and low spots in the drain tile are the usual problems. If a drain-tile system is not present and proper surface drainage doesn't stop the leak, install an interior drain-tile system. A properly installed system should eliminate this type of basement leakage and help ensure a dry basement. For tips on installing an interior drain-tile system, see Concrete Repair Digest, December 1992/January 1993, p. 261.