The definition of “wet” may vary from one homeowner to another. For the purpose of this article “wet” shall be defined as visible water collecting on the floor. A wet basement, by this definition, would have 1/4″ or more of standing water on the floor. It is important to differentiate between a wet and damp basement. Dampness can mean that you have a humidity problem. Wetness means that you have a water problem.
Understanding Basement Construction
Construction is the key factor in why the basement gets wet. When building a St. Louis home, the contractor digs down approximately 8-10 feet, which creates a bowl-like formation in the ground. Concrete footings are installed, which will bear the weight of the structure. After the footings are placed, the contractor will either pour a concrete wall or install block to grade. The contractor will then pour a 3″-4″ floor for the basement.
On the exterior the contractor will “damp proof” (not waterproof) the wall and a 4″ perforated drainpipe will be installed around the perimeter of the basement to help prevent water intrusion. Unfortunately, these preventative measures usually prove to be minimally effective.
After all of this, the exterior area around the basement is then backfilled. The soil that has been backfilled creates optimal conditions for basements to leak. The soil that is used in backfilling the basement is much looser and more aerated than the compact virgin soil that surrounded the building. This is due to the fact that soil was dug up and then replaced. Although it can be mechanically compacted, it will never be as dense as the virgin soil 5′ to 10′ out from the foundation wall.
How Water Gets Into Your Basement
Now that you understand the way a basement is built, it will help in understanding how the water gets into your basement. Here’s what happens when it rains:
- When it rains, water sinks into this backfill area and saturates it. The water will saturate the backfill area between the virgin clay soil “clay bowl” and the foundation. This shape in the soil will naturally direct the water toward the footing/wall intersection at the base of the foundation, exerting pressure on the foundation.
- Contrary to popular belief, water cannot pass through concrete unless there is a visible joint or crack. Therefore, the rainwater that has saturated the soil and is exerting a pressure on the outside foundation wall will find the path of least resistance. That path is usually a crack, joint, or the floor/wall seam at the base of the foundation wall.
Understanding Water Tables
The common belief is that water rises through a water table. Although the water table underneath the home does have the ability to rise, the reality is that the mechanics described above are the reason why basements typically get wet. Very rarely will the water table rise to the point of flooding a basement.
*Kent Foundation Repair only offers Basement Waterproofing at our St. Louis service area.