Interior Drainage Systems

Photo of drainage system pipe inside basement.Drainage systems can be installed on the interior of your foundation as well as on the exterior. Both systems are generally the same and accomplish the same goal, conducting water away from your foundation. The materials used and methods of installation differ between the two systems with the main difference being that interior drainage systems utilize a sump pump located in a sump “collection” pit. The drainage or “tile” system will conduct the water to the sump pit where it collects. Once the water level in the pit reaches a predetermined height, the sump pump will engage and discharge the water through solid conductor pipes to the outside of your home. This discharge pipe will either be tied into existing exterior conductor pipes or run to discharge at a point in your yard far enough from your foundation to no longer be a concern.


While exterior drainage systems are usually installed during construction, they can possibly fail over time due to the use of low cost materials, poor workmanship, or unforeseen natural conditions. This will result in a wet basement. Also, hydrostatic pressure beneath the basement floor slab can sometimes force water to the surface via a wicking action, through cracks in the floor, or through the cove joint (where the wall meets the floor). An exterior drainage system will not resolve this situation. An internal drainage system is a much more cost effective solution on existing homes rather than excavating the entire foundation in order to install an exterior system. Interior drainage or “tile” systems are often regarded as a complete solution to control or prevent just about any type of moisture seepage. In situations where hydrostatic pressure is forcing water through the floor slab, an interior drainage system may be the only solution.

Photo of circular holes bored in concrete along floor.Once water has penetrated CMU walls, or walls built with concrete blocks, it can be held within the webs of the blocks and build up, resulting in hydrostatic pressure. Walls holding water will discolor, tend to weep, and could possibly degrade over time if the problem persists resulting in a wall that is no longer structurally sound. With an interior drainage system in place, holes or “weep” holes are drilled into the bottom course of blocks allowing them to drain into the system, thus relieving the hydrostatic pressure.

Sump Pit

In order to install an interior drainage system in your basement, 12 to 18 inches of the concrete floor must be jackhammered and removed from around the perimeter of the basement wall. A trench will then be dug between the foundation footer and the edge of the concrete floor slab down to the bottom of the footer. A determination must be made as to the best position for the sump pit in relation to the intended discharge point. More concrete will need to be removed from this location to accommodate the installation of the sump pit.

Illustration of water being funneled into sump pit inside basement.

Once the location is determined, the pit can then be excavated and the pit liner can be positioned within to rest flush with the concrete floor. At this point weep holes will be drilled into the course of blocks resting directly on top of the footer to enable the water trapped within the walls to drain into the tile system and be conducted away. A minimum of 2 inches of washed gravel will then be placed in the freshly dug trench. A 3 inch perforated, high-density polyethylene triple wall pipe will then be placed, perforations down, on top of the bed of gravel with special attention being given to ensuring that it slopes towards the sump pit for proper drainage.

 Water Diverter

Once the proper slope is achieved, the pipe will then be connected to the sump pit. Triple wall pipe has 3 bonded layers to provide an exceptional pipe stiffness rating at least double that of any competitive pipe. More washed gravel will then be placed in the trench to completely cover the pipe. The gravel should be flush with the bottom of the floor slab. A seamless water diverter will be positioned over the weep holes that were previously drilled and will extend out over the tile. This diverter ensures that any water coming out of the walls makes its way down to the drainage system rather than onto your basement floor. The sump pump can now be installed in the sump pit.

Pipes will be attached to the pump and run outside in order to discharge the water that collects in the pit. Once everything is in place and connected, the operation of the pump can then be checked to verify that the system is functioning properly. Many homeowners elect to install a battery back-up sump pump as well. In the event that a storm would knock the power out, the battery back-up would kick in and continue to discharge the water from the sump pit, ensuring that your basement would not flood. The last step in the process is to place 4 inches of concrete in the trench and blend it in with the surrounding basement floor.

At Preferred Basement Solutions, we understand how frustrating a wet basement can be for a homeowner. It is our goal to provide the right lasting solution for any moisture problem after first evaluating all possible factors and potential causes. Interior drainage systems can solve a wide range of basement moisture issues, giving you peace of mind in knowing that your basement will stay dry for years to come!