Why Basements Leak
Wes Kelley, Certified Inspector
7 Oaks Home Inspection, LLC
As inspectors working in the Midwest we see quite a few basements. The biggest complaint or concern we hear concerns a moisture related problem. There are three basic reasons for a basement to develop a leak or a moisture problem. Sometimes a little detective work is needed to figure out the problem.
Picture this. A ten year old single family home with stick built construction setting on a full basement. The basement walls are eight foot tall but the house sets only one foot above ground level. Water from the downspouts have continually discharged next to the foundation for ten years. The dirt around the foundation has settled and the foundation has a few vertical shrinkage cracks. Water comes into the basement almost every time it rains. This is not an uncommon problem seen many times over by home inspectors. What is the issue? Why did the water pouring off the roof come into an eight foot hole in the ground lined with porous material that has cracks? The problem is a combination of hydrostatic pressure and negative grading and improper downspouts working together to form a “perfect storm” of water into the basement.
Hydrostatic pressure is the term used to describe water that builds up vertically along the side of the foundation walls. The higher the vertical column of water the more the weight of the water causes pressure to build. Water always takes the path of least resistance and the vertical concrete wall is generally the path. This water, as it builds up, pushes it’s way into a basement and causes moisture problems. During a dry season like we had in this area this year, soils contract and generally cause open areas along the basement walls. Water easily enters these voids with no problem. Ideally water should have been diverted away from the house through the down spout system. Many times simple splash blocks are used at discharge ends but this water still diverts around the foundation area. A wise way to get the water away from the house is to install a gutter extension at least ten feet from the foundation. This generally gets the water past the over dig on top of undisturbed soil. It is best to place these systems underground for esthetics and to eliminate a trip hazard.
The next issue deals with grading. This term refers to the soil around the foundation. Does the soil pitch or slant toward the foundation? This is called negative grade. Or does the soil pitch away from the foundation? This is called positive grade. Over a period of years the over dug area of a house foundation will generally settle and cause a negative grade situation. Instead of the water flowing away from the residence it actually flows toward the residence creating a moat area around the house. A home should have a one quarter inch per foot slope for the first ten feet away from the house. This will allow rain water to divert away from the house. Mulch beds for flowers and bushes will not correct the problem. Mulch is not considered “soil” because water will still work through the mulch until it gets to the soil area. If you have negative grade under the mulch, water will pool against the foundation and work its way through to the inside of your home.
Downspouts and gutters are very important to keep water from working into your foundation. For gutters to properly function they need to be free of leaves and twigs. Downspouts need to be properly sized, connected and pitched in order for the system to function as designed. If you see water cascading over your gutters during a heavy rain, you know that one of these issues need to be addressed. There are many products that assist the home owner in keeping gutters clean and free of trash. These products are especially helpful if you have a home that is close to trees. Addressing the areas of proper grading and guttering should go a long way in helping you maintain a dry basement.