Why do basements leak?
Honestly speaking there are many different opinions on why basements leak and most people in the waterproofing industry believe that they have the correct answer. After years of hands-on experience and research, I have found that most professionals have a very narrow opinion of why basements leak. If you search for answers on the internet you will often be led to a link that takes you straight to their website for a quote. The truth is basements leak for different reasons depending on several factors. Hydrostatic or lateral pressure is the most common factor for a leaking basement. However, all below-grade foundations are under Hydrostatic pressure so the question becomes why does your foundation leak? Here are some of the facts on why foundations leak.
Age: When homes are built in most cases exterior waterproofing is done to prevent water intrusion. Years ago, many builders used tar and plastic around the exterior walls and footing. More recently builders are utilizing roll-on or spray applications to prevent water from entering the foundation. An exterior drainage system near the footing is also used to redirect water by some builders. Interior waterproofing systems using ADS or PVC pipes and a sump pump are also used to manage water intrusion.
Exterior applications are exposed to the outside elements causing exterior membranes to deteriorate and allow water to come into direct contact with the foundation. The minerals and chemical deposits in water will break down the coating and weaken the concrete. This facilitates cracks, holes, and gaps which leaves the foundation open to structural damage from Hydrostatic pressure. Interior drainage systems and sump pumps help to relieve foundation pressure by allowing the water pressure to be released and redirected to the sump pump and discharged away from the foundation. Interior drainage systems can also become clogged by mud, dirt, sand over time and pumps can fail with age. Just remember as we go through the aches and pains of age, so does our foundation.
Foundation cracks: The most common foundation cracks are settling, shrinkage, shifting, and expansion cracks.
A foundation will experience some settling which can cause cracks in corners, doors, and at the windows. Settlement cracks are caused by changes in the soil or improper backfilling during construction. Concrete can also shrink over time and cracks will develop. Both settlement and shrinkage cracks may leak at some point and are troublesome but normally they are not structural if they are narrow and run vertically.
Cracks that are horizontal or appear in a step pattern may indicate a shift in the foundation and allow the crack to expand under pressure and climate change. These cracks are more serious and need to be addressed as soon as possible.
Negative grading: The grading surrounding the house or building can have a negative effect on the foundation. A hill or slope will toward the foundation will cause water runoff to pool against the foundation and cause major problems.
Gutters/Downspouts: Gutters and downspouts are designed to protect the foundation by redirecting water away from the foundation during a weather event. When they leak or become clogged, they do just the opposite. They dump massive amounts of water against the foundation causing soil erosion and added pressure against the foundation. So basically, water from the roof floods the basement.
Soil type: The type of soil surrounding the foundation plays a part in why foundations leak. Some foundations leak only when it snows and not when it rains. This has puzzled many of my clients and believe it or not, some professionals as well. Different soil types react differently when exposed to water. Soils with a high level of permeability such as sand are more likely to allow water to penetrate the foundation much faster. This is because sand is made up of loosely formed granules that separate easily when exposed to water. In contrast, clay when exposed to water will stick together and has less permeable features than dirt or sand. In the case of foundations that leak only during a particular weather event such as snow. This is because water has caused the soil to separate and then freeze. The frozen water will expand and cause large voids in the soil. When that water starts to thaw, it has direct access to the foundation which it does not have during a normal rain. People are also perplexed by the fact that their basement does not leak unless there is a drought prior to it raining. Clay has less permeability than some of the other types of soil mentioned however, if clay becomes extremely dry it can shrink up and crack. This leaves large gaps for water to go straight to the foundation without the normal protection clay provides when exposed to moisture.
In terms of why foundations leak I have listed some of the most common causes. My attempt is to provide you with some basic knowledge without tempting you a write a book titled "why I want to move to an apartment". I hope I have people understand why and how water enters their basement. The fact is that there are many different reasons why this could be happening. I also want to educate you so that you are not so easily dupped by salesmen posing as inspectors. The truth is you and your neighbor may both have problems in the basement and have two different reasons why this is happening. Hydrostatic pressure is always there but homes are built to withstand that pressure. The real question is where is the weakness in the foundation that is allowing the water to enter, and how can I help protect my house in the future.