Underslab plumbing leaks can pose unique problems for commercial and residential foundations. They can be leaks that have been occurring gradually over time or a sudden catastrophic leak that occurs suddenly. In the southern United States much of the incoming water is routed through pipes located in the attic. Leaks in these pipes are relatively easy to repair because they are easy to access. However, usually the outgoing sewage and waste water is routed underneath the concrete foundation. The pipes are located in soil and have a gradual downward angle until they connect with the main sewer line or septic tank.

If an underslab plumbing leak is suspected then the commercial or residential property owner should call his or her property insurance company for assistance. In some cases a homeowner's insurance policy will pay for tests to determine if there is leakage in the sewer drain lines. And in some cases an insurance policy will pay for damage caused to a foundation by a broken sewer line. In almost every case these tests must be performed before any foundation repairs are initiated. Unfortunately, most insurance policies do not cover the cost of repairing sewer line leaks. Also, they usually do not pay for any plumbing problems related to the leveling of the foundation by the repair contractor.

Under slab plumbing leaks may be present for many years before they become evident. Since the sewer system is draining waste water and sewage there is no increase in water usage to alert the home or property owner. Generally speaking, homes and structures built before 1974 were built with cast iron sewer lines. Cast iron is subject to corrosion and can be easily broken when there is soil movement under the foundation. Concrete pipe was also used as sewer lines before 1974 and any sewer system constructed of cast iron or concrete that is forty years old or older should be inspected prior to any foundation repair. After 1974 a hard plastic, PVC, was and is used as the predominate material for sewer line systems because of its longer life span and other advantages.

Large volumes of water that leak underneath the concrete slab of the property or home will cause the expansive soils to swell in volume. This creates a "mound" or "hump" in that area because of the swelling soil. Soil that is outside of the immediate area of the leak will remain relatively stable because it is not influenced by any variation in moisture. This "soil hump" under the foundation will create an uplift and can cause severe foundation damage as well as additional damage to the plumbing system.

Smaller volumes of under slab water leakage can have a different effect on the soil. It can result in the "settlement" or further compaction of the soil. When this happens a void will be created between the bottom of the concrete foundation and the soil. If the area of the void is large enough then the weight of the building or home plus contents can cause the foundation to crack or sag. In these cases the foundation will need some additional internal support and the void is usually filled with a concrete/mud mixture.

It is always a good idea to check for under slab plumbing leaks prior to the purchase of a home or commercial building. This is particularly true if the property is older than forty years of age. This will protect the buyer from unanticipated underslab plumbing leak problems and potential foundation repair problems.

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