At the beginning of this month, a landslide in North Salt Lake destroyed one home and caused 27 others to be evacuated. People are rightly concerned about protecting their homes from disasters such as this. When things like this happen, we are all reminded that Utah is not immune to natural disasters. While we would drive ourselves crazy if we thought about the possibility of landslides and earthquakes every day, it is important to not live in complete denial either. We need to understand the risks and know what we can do to protect our homes against potential damage as best we can.
As part of a major home renovation, this family also replaced their failing railroad tie retaining walls with structurally engineered concrete retaining walls. (Kevin Bunnell, Renovation Design Group)
Because landslides are such a current issue, let’s talk about them today.
A landslide is when masses of earth, rock or debris move down a slope. This can happen because of natural erosion or in combination with heavy rain, floods, storms, earthquakes, volcanic eruptions or proximate construction when the soil is disturbed. Just days before the North Salt Lake landslide, there was a massive human-induced landslide in India, while a few months before that a natural landslide wiped out a whole town in Washington state. And as we were writing this article, the news broke about the landslide in Japan’s Hiroshima.
The point is that landslides happen all over the world in every soil type and climate. According to information from the Utah Geological Survey (online at geology.utah.gov), they most commonly occur as a result of natural conditions such as heavy rainfall or rapid snowmelt, or due to man-made conditions including grading that alters a slope or the addition of water to a slope from agricultural or landscape irrigation, roof downspouts, or broken water or sewer lines.
The only sure way to protect your home against a landslide is to not build your house on or near a slope. However, we tend to love hillside homes and their attendant views, so we build on all types of lots.
There are some things that can be done to reduce the likelihood of landslides. If the slope in question is solely on your property, these mitigating actions will be in your control. If the slope is larger in scope, you should consider who will be in control of these issues.
Outside drainage
According to the Utah Geological Survey, a homeowner needs to carefully manage water that naturally occurs on his or her lot, as well as water that is added in the form of irrigation and plumbing. Storm water runoff from downspouts and hardscape areas (such as a concrete driveway) should be directed so as to drain away from exposed sloping areas. Minimize landscape irrigation, especially on the top of a slope, as overwatering on bluff-tops is a common cause of landslides. In addition, make sure water and sewer lines are not leaking.
Retaining walls
Retaining walls are designed to restrain dirt and stabilize a hill. While the average retaining wall will not be able to hold back the pressure of a massive landslide, it will help to stabilize a managable slope and help contain smaller soil movements.
Ground cover
You can also protect your property by planting ground cover on slopes to stabilize the soil. Not all plants work to help prevent soil movement. We recommend consulting a professional landscape designer or landscape architect to help determine the best plants for your slope.
Get professional advice
If you are dealing with a slope large enough to pose a danger to the house itself, it would be wise to consult with a geotechnical consultant/civil engineer for advice. Ideally, this would be done prior to making the decision to purchase such a property. If it is too late for that, geotechnical engineers can do a ground assessment and help determine the best placements of retaining walls or other soil stabilizers (such as grout curtains and concrete anchors), or if deflection walls would be advisable.
In the end, the buck stops with the homeowner. The Utah Geological Survey has a section of advice to homeowners and homebuyers that is worth reading. They point out that investigating a piece of property is the homeowner’s responsibility. Utah law does not require Realtors to verify or disclose geological hazards. In addition, one should not assume that approval of a subdivision by a local government authority guarantees safety from geological hazards. The final blow is to know that losses due to geological hazards are normally not covered by basic homeowners insurance.
There is more to buying a house than loving the new kitchen or coveting the three-car garage. Your home may be the biggest purchase of your life, so serious study and analysis is called for. In our dry climate, some hazards may lay dormant for years, including the danger of landslides.
A wet spring or summer is a timely reminder that Mother Nature is not to be ignored!
Ann Robinson and Annie V. Schwemmer are the principal architects and co-founders of a residential architectural firm focused on life-changing remodeling designs at RenovationDesignGroup.com. Send comments or questions to ask@RenovationDesignGroup.com