How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
site-built, mobile/manufactured and modular homes
How can I tell whether my house foundation problems are caused by a sinkhole or expansive clay soil?
Friday, August 30, 2019
Because the crack patterns can be similar, it often requires an engineering evaluation of the soil under the home to find out what is causing the structural distress in your walls. Soil boring samples and ground-penetrating radar are two tools used make a determination.
But there is one generalization that might point you in the right direction. Sinkholes increase during times of extremely wet weather—such as after a hurricane or series of thunderstorms—because they are caused by water dissolving the karst rock layer beneath the soil overlay, but clay soil problems are the worst during periods of drought.
Clay soil expands when the moisture in the soil increases, and shrinks when it dries out; yet the problems tend to be more pronounced when the soil drops during a prolonged drought. During one drought in our area a little over a decade ago, wells went dry and soil subsidence induced by clay soil was at its worst.
Also, sinkhole problems tend to be an event that happens over a short period of time. The up-and-down movements of clay soil, although smaller, are cumulative and crack up the walls of a house gradually over time. So houses more than about 10 years old are very likely to show signs of movement of clay soil below, if it is there, but a sinkhole can appear at any time.
Many sinkholes are not the house-swallowing variety that make the news. The house is not at the bottom of a big hole, but walls are severely fractured, while sunken areas and pits in the ground around the home indicate the sinkhole activity.
Clay soil is easily recognized by the crack patterns in the surface that occurs when it dries out, like in the photo at the top of the page. Florida, unfortunately, has much of its clay soils buried in veins below the sandy soil on top. The Hawthorne Formation, a geologic layer which underlays some parts of the state, is one example.
Clay Soil Damage Not Covered By Insurance
Whether the structural damage to a home is caused by a sinkhole or clay soil is often a point of contention with insurance companies. Clay soil is considered an existing condition, and not covered, while a sinkhole is covered. And there can be differing options between engineering firms hired to assess the situation as to which one it is.
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To learn more about exterior walls and structures, see these other blog posts:
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