Soil Types Affect Your Foundation

Types of Soil in Chicago

The type of soil underneath your foundation will determine its stability. For the most part the Chicago area is made up of 85% clay and and very little loam soils. These types of soil can either absorb lots of water or evaporate quickly with mini droughts. This is perhaps why sometimes you may notice your cracks on your walls close up with wetter water conditions and open up during drier conditions. Structural engineers call a this type of foundation that moves with the seasons a “floating foundation”.  Because of the weak soils we have in the entire Chicago area homes will settle and sink causing damage to your home.  This is why your home needs to be underpinned where the load of your home must be transferred onto steel pipe piles deep into the ground to near rock-solid ground.

It’s important to have your downspouts properly working and keep them at least 10′ feet away from your existing foundation. Another  important factor to keep in mind is the grade level pitch  must be properly pitching away from you home, otherwise this could cause lateral soil pressure onto your foundation wall causing it to fail and bow.

All homes will settle a little, but some homes will settle more noticeable than others, especially if the foundation of your home or room addition is shallow or above the frost line. Here in the Chicago area all foundations must go below 42″ deep to keep  in line with village codes and to be below the frost line (to minimize shifting). If your foundation is shallow (less than 42″ deep)  it has a higher probability of settling and sinking. 

Most Common Types of Soil

  • Clay – A soil with a highly expansive texture and is easily molded when wet. It is composed of very small particles and can easily shrink  and expand. Not suitable for shallow foundations or if the ground gets to wet or too dry. – Not the best type of soil to support  foundations especially a shallow foundation (Room additions, Garages, Enclosed Porches Etc.)
  • Loam – A soil made  up of sand, clay, and silt, with this type of mix and perfect weather conditions this soil is ideal for building homes on, unfortunately only little spurts of the Chicago area have this type soil. 
  • Peat –A soil type  made up of decomposed plant material, which has built up over something like 10,000 years in poorly-drained wetland habitats – NOT ideal for supporting a foundation.
  • Silt –A type of soil that is granular material of a size between sand and clay. Alone not a suitable for drainage purposes can remain mostly moist and cause a foundation to absorb water leading to a very damp and wet basement.
  • Gravel – Very large spaces between particles, very little moisture retainment. – Ideal for drainage systems.
  • Rock – A type of soil made up of limestone, bedrock, sandstone, or another rock. It is solid and doesn’t absorb moisture. – Ideal for supporting a foundation.