Avoiding Costly Homebuying Mistakes: Never Underestimate the Power of Dirt
by Lawrence M. Kostaneski, P.E.
During my 10 years as a City Engineer, I was often amazed - not to mention appalled - at what certain soil types could do to a house. Here is a true event typical of the many I observed.
A woman called one day and asked me to look at her house foundation. The house was built into a gently sloping hillside, with vehicle access from the alley in back. I knew the soil type in this area and expected the usual symptoms. I slightly underestimated. The symptoms had grown to become a destructive and heartbreaking sight. The concrete wall on the west side of her basement leaned so far east that it had cracked from top to bottom in three or four places and left 75% of the floor edge above unsupported. A Contractor had placed huge metal jacks, wedges and similar devices to prevent the first floor from failing completely.
I decided she wasn't seeking advice as much as consolation and guidance. I told her that the Contractor seemed to know what he was doing, which was true. What bothered me most was the sense that this woman became deeply troubled by all this and would remain troubled long after the wall was repaired.
The obvious is the thing that stands the greatest chance of escaping our attention. Take the earth, for example: not in the geophysical sense, but as in dirt. Engineers call it soil. (It took us thousands of dollars, years out of our lives and untold hours of Calculus homework to be able to make this distinction.).
Soil is a remnant: it represents the crumbs and table scraps of the geologic process. Soil types are as varied as the geologic processes that produced them. Some are quite stable and don't change much; others can be fickle and unpredictable. Certain types of clays are in a family described as Expansive Soils. (You could substitute the word "Expensive" and not lose much in the translation.) Clay's chemical makeup is such that the water trapped between the particles is absorbed, causing the soil mass to swell dramatically. Concrete basement walls will move and floors will crack because of this phenomenon. Roads buckle, driveways shift, and walls collapse. It is not a pretty sight, as the woman in the above story could attest to.
Silt is another nasty soil type. This soil is the result of water deposited material. Silt also has a catastrophic affinity for water, but with a different result. The water acts as a lubricant between the soil particles, turning the whole thing to mush. Given the choice, I'd take Clays every time.
Organic soil types have a high percentage of decayed vegetation. These soils are excellent for growing bragging quality gardens and beautiful lawns, but they present some construction problems.
Soil types range from rock to quicksand. Most soil is a mixture of clay, silt, sand, some organic material, rocks and gravel. It is the proportion of ingredients in a soil, and how that proportion affects the behavior or "stability", which designates the soil type. A soil with predominately clay particles is classed as a clay type soil -- providing it behaves in the "classic" fashion of clay soils.
If you are considering buying a home, ask the builder/developer/realtor about the soil. Don't be surprised if NO ONE on your team (unless you include a Professional Engineer, which is unlikely) can even tell you the soil type much less explain its tendencies and characteristics. Based on the unbelievable things I have seen bad soil do to a home, it is worth the effort to find out about the "dirt" in your neighborhood.
Mr. Kostaneski is a registered professional engineer with over 20 years experience in the design and construction industry. He is President and Owner of Centerline, an engineering consulting firm. Comments are from his book, "A Home Buyer's Guide To Reality".
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