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Chicago Structural Foundation Damage: Is Wet or Dry Weather Worse?

Jul 27, 2013 • By Matthew Stock.

Wet Dry

Incurring structural damage to its foundation is one of the worst things that can happen to a home short of a natural disaster.  A severely damaged foundation will impact the stability of the entire structure and can require extensive repairs, not just to the foundation but to the entire house.

Many homeowners are surprised to learn that foundation damage typically is not attributed to faulty design or construction.   Although it is true that an improperly prepared building site can lead to foundation problems, the damage usually occurs over time as weather conditions affect the soil that surrounds and supports the foundation.

The two common types of structural foundation damage — tipping, rotating or bowing walls and extreme dropping or sinking – are both caused by changes in the water content of the soil in which the foundation sits.  Although there is always water in the soil, at some depth, it is the extremes — too much water or too little — that cause the damage.

Foundation Damage from Wet Weather

When soil that surrounds a residential foundation becomes saturated, the water must either drain off or be absorbed.  Some soils, like sandy soil or loam, drain fairly well and are less likely to set the stage for foundation damage. Clay soil, on the other hand, the most common soil type in the Chicago area, is extremely absorbent and doesn’t drain well at all, often making it the culprit.

When clay soil absorbs water, it expands.  When the expanding soil meets the foundation wall pressure begins to build and it is usually the wall that gives way.  In many instances, this results in only a narrow, non-structural crack that may allow water to seep into the basement but is not a threat to the structure.  When the pressure is extreme, a concrete foundation wall may crack enough at either end that it begins to tip or rotate inward, separating from the sill plate of the frame structure above.  A concrete block or other masonry wall will crack at the mortar joints and masonry units in the middle will move inward creating a bow or bulge.

Foundation Damage from Dry Weather

Of course, there is almost always water in the ground, the level of which in a particular area is called the “water table.”  During times of little rain, the water table will remain fairly constant, unless the problem becomes severe.  When this occurs, as it did in the Chicago are in the summer of 2012, the roots of trees and shrubs begin to send their roots deeper and wider in search of moisture and they draw more and more water out of the soil, a process known as “desiccation.”

When this desiccation reaches the soil at or below the base of the foundation, serious trouble can occur. Just as soil expands when it absorbs water, the same soil will compact as it gives up its water and the weight of the home and its foundation press down on it.  Once the water (and any existing air) is driven out, the compaction or shrinkage of this soil may be so great that the house actually drops or sinks.  Typically, this will damage foundation walls, separate the foundation from the aboveground structure and cause cracks, jammed doors and windows and other damage to the house.

Of course, both types of damage are reparable, requiring stabilization of the walls in the first case and underpinning of the foundation in the latter.  The wall damage caused by overly wet conditions is arguably less serious but neither type of damage is to be taken lightly and steps must be taken not only to repair it but to prevent it from getting worse or recurring.

If you see signs of either kind of structural foundation damage, you should seek out the advice of an expert.  At U.S. Waterproofing, our structural foundation experts use engineering data to accurately diagnose foundation damage and the least disruptive techniques to remedy it.  Why not ask us for a free consultation?

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