There are several factors unique to the Salem area that leave foundations at elevated risk of problems. We’ll discuss these in detail below and offer some insight into how each creates a problem for your Salem home.
Frequent, Heavy Rainfall
Oregon is well-known for its excessive rainfall. While Salem only receives 45 inches annually – about 50% more than the national average – the city experiences persistent precipitation, nearly half of the days each year. The above-average and regular rain in Salem put foundations at high risk of water intrusion.
Runoff is exposed to your foundation as it soaks into the ground, and heavy rain means the concrete will be wet for long periods. The longer moisture can interact with your foundation, the more likely it is to find its way inside, either through pores in solid concrete or through foundation cracks. Water and moisture below your home can present numerous problems, including mold growth, pest infestation, and water damage.
Additionally, Salem’s soil is heavier and slightly more voluminous when it gets wet, as it has a moderate level of absorbent clay in it. As the soil expands with the constant rainfall, it puts added pressure on your foundation walls and slab, sometimes causing them to crack from the immense stress. The cracks can leave you with structural damage and make water intrusion more likely.
Seismic Activity
Oregon is considered to be at moderate risk of earthquakes. Although residents fear what is commonly referred to as “the big one,” an expected earthquake of 8.0-9.0 on the Richter scale originating in the Cascadia Subduction zone, most quakes are minimal in the area.
However, even small ground movement can cause foundation damage.
The ground can shift and settle slightly during earthquakes of minimal intensity. Concrete is rigid and unable to flex with ground movement, so the shifting caused by earthquakes can leave portions of your home unsupported by the soil around it. Foundations without support typically crack under the pressure.

To make matters worse, the earth’s settling in response to quakes can happen at varying rates under and around your home, leading to a process called differential settling. This phenomenon can cause sections of your home to sink more rapidly than others, leading to cracking across your foundation and the loss of structural integrity.
Tree Roots
Tree roots are surprisingly resilient and powerful, and they can cause several types of foundation damage in any area. However, Salem has named Ailanthus altissima – colloquially, the “Tree of Heaven” – as an invasive species that is a significant issue for homeowners and business owners in the city.
The tree is characterized by very rapid root growth and abundant absorption of water from the soil. The thick roots can quickly damage foundations, forcing the concrete inward and sometimes creating large rifts in concrete walls.
The roots also soak up excess water from the soil around them, which creates wildly varying moisture levels in the ground. The clay in Salem’s soil swells and shrinks with changes in water content, so the Tree of Heaven contributes to differential settling of the earth, which can cause significant property damage and instability.
Radon
Lastly, radon is prevalent in Oregon, and Salem is at moderate risk of the associated hazards. Radon is a radioactive gas that can seep up from the ground into your home. Cracks and weakness in the concrete under your house can contribute to radon issues, but most foundations in the area need to be sealed to prevent radon from entering your living space.
Radon isn’t believed to cause damage to your home, but it is hazardous to your health and should be addressed as seriously as structural damage.