The difference between a soil scientist and a soil engineer is pretty significant. While the scientist is generally concerned with soil’s biological properties — what can be grown in it — an engineer is interested in what can be built on it. (That these disciplines rarely cross paths is one of the many ironies in our disjointed professional services industry.) So when I heard about a man who watered around the outside of his chimney in the hot summer months, I wondered if there was something I missed in school.
As it turned out, this man’s home was one of many that had been built on the clayey soils of Sonoma County in Northern California. Clay is highly expansive in nature due to its very fine particles, which give it a tendency to retain water rather than just let it pass through. So in the wet months of winter, the soil beneath his chimney expanded and pushed up on the footing that supported his chimney, and in the dry summer months the soil contracted and settled, causing his chimney to lean. When he understood this phenomenon, he smugly took matters into his own hands by keeping the area around his chimney wet year round.
Today, the chimney-watering man’s home would probably be built on what they call a drilled-pier-and-grade-beam foundation rather than a shallow continuous spread footing. Such pier foundations rely on soil friction and a sort of upside-down beam to resist heaving. Since it would be cost prohibitive for him to replace his entire foundation, one recommendation would be to dig down and remove as much of the clayey soil as possible, jack the home up and pour reinforced concrete haunches to support the settled portion of the home. Helical piers would be another option. I have used both of these solutions for homes in the past.
Regardless of the solution used to remedy this kind of structural problem, there is one thing that I discussed with both of these home owners that I want to share with you. You’ve probably heard it before — “An ounce of prevention is worth a pound of cure.” So, what’s the prevention?
Simply put, keep water away from your house. Before the first owner of your home occupied it, a grading verification was performed by an engineer that certified that under normal conditions water would be kept away from your house during rain storms, thereby preventing water from ponding around your foundation and causing problems. All it takes is a gentle slope away from the house and properly designed inlets for water to be collected and directed out to the storm drain pipe that runs beneath the street in front of your house. I have seen too many home owners that mucked with the original landscape design by hardscaping too high and without adequate slope, blocking inlets, etc. They are setting themselves up for big problems down the road, especially if their home is on clayey soils.
In short, the man who watered his chimney was trying to apply bandages to a problem that could have at least been lessened by better grading. While there are structural remedies to homes that have experienced settling due to water build up, clayey soils, and poor grading practices, they are costly.
If you have any questions or concerns about settling issues or the grading of your home, please feel free to contact me.