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 avoid buying a house with clay soil heaving foundation problems?
Sunday, September 1, 2019
It’s necessary to understand the mechanics of how expansive clay soil damages the foundation of a house, and in turn creates cracks in the walls and floors, in order to know what to look for when house hunting. Clay soils are highly water absorbent. They act like sponges, expanding and shrinking according to their moisture content.
But, unlike a sponge, the change in moisture level happens slowly over months and years. And even if the expansion and shrinkage of the soil level is not that much, the repeating heaving upward and then dropping back down of the foundation creates more damage with each cycle. Uneven moisture changes in the soil under the home due to tree roots absorbing water, or a leaking pipe or sprinklers adding water, in a limited area also creates differential settlement, with one area shifting while the surroundings are stationary or moving in the opposite direction.
Some parts of the country have clay soils visible at the surface. Expansive clay sticks to your shoes when wet and the surface develops a web of cracks when dry. But clay is often in a layer below the top soil. Neighborhoods may have veins of clay running under them, so that one cluster of houses may have a clay soil problem and the nearby homes are fine.
Here's a few ways to avoid buying a home with clay soil problems:
1) Buy a house that is ten years old or more. This resolves several potential issues:
- There is an initial change of soil moisture after the site is cleared of trees and other vegetation and the house is built.
- Homes built on clay soil take longer for the initial settlement in reaction to the weight of the new home on the ground. One expert suggests that this can take up to 20 years, compared to just a couple of years for sandy soil.
- A home is likely to have gone through at least one drought or excessively rainy season during a decade.
- So if there is a layer of expansive clay soil under the home, it is likely that you and your home inspector will see cracks as evidence of it.
2) Talk to people nearby. We have worked in areas that had both expansive clay soil and sinkholes and, when the foundation repair company shows up with their big trucks and pneumatic equipment, everyone in the neighborhood knows about it. Neighbors, local home inspectors, and the building department can tell you which areas tend to have more problems if you ask. There are a couple of neighborhoods on the west side of Gainesville, for example, that seem to always have a RamJack® crew working somewhere in them each time we are there doing a home inspection.
3) Look around the exterior carefully. Search for cracks at windows, doors, and corners, including examining the wall obliquely for the subtle evidence of repaired cracks. Ideally, the grade should slope away from the house on all sides, a gutter and downspout system discarges water at least five feet from the house, no big trees overhang the house, and there is no standing water near the house. This is good advice for any house, but extra appropriate if you are in an area with clay soil.
4) Hire a home inspector that has been working in the area for at least five years. That’s long enough to know their way around the different neighborhoods and geography of the land. Tell the inspector about your concerns. A home inspector is not qualified to tell you definitively that any visible structural distress is caused by clay soil, but the inspector can point you in the right direction for further evaluation if it looks like it's necessary.
5) Hire a geotechnical engineering company to evaluate the site. This is not cheap, and proably only sensible if you are buying a pricey home in an area with questionable soil stability. But it is an option. They will take soil boring samples, and possibly use ground-penetrating radar, as part of their work before they issue a comprehensive report.
We know you are not going to buy a house with cracks like the one in the photo at the top of the page, but the point here is to steer away from one that is likely to, or just beginning to, develop structural problems. Also, see our blog post How can I tell whether my house foundation problems are caused by a sinkhole or expansive clay soil? and Where are the places to look to find structural cracks in a house?
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To learn more about exterior walls and structures, see these other blog posts:
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