How Foundation Soils Can Affect Your Foundation
Your home is resting on a combination of different types of soil. These soils affect your home’s foundation in different ways under different conditions. Under the worst variety of conditions, your foundation soils can produce a severe effect on your home, leading to all manner of foundation or structural issues.
Different types of foundation soil are sandy soils, clay soils, and sandy loam soils. Each of these expands and contracts differently, exerting different levels of pressure on your foundation under certain conditions.
The soil you should be most concerned with is the soil in the most immediate proximity around your home, referred to as the Active Zone. The Active Zone refers to the soil around and underneath your home, varying from a few feet below the surface to as much as—or even more than—30 feet below.
Causes of Foundation Settlement
Foundation settlement refers to how your foundation moves when soil fails to support the weight of your home. There are several causes of foundation settlement, including drying and shrinking soil, poorly compacted fill soil, and wetting and softening.
Drying and Shrinking Soil
Drought, or extended dry periods, will dry out the soil and cause it to shrink. Soil that shrinks can create pockets of space or voids. When this happens, it is usually your foundation that sinks to fill the void.
Large, mature trees are another cause. Trees have extensive root systems, which may reach under your home if a tree is close enough. As a tree matures, it soaks up more and more water from the soil, causing that soil to dry and shrink.
Poorly Compacted Fill Soil
When your home was first constructed, contractors needed to excavate the area to make room for your foundation. Digging up all that soil loosens it, leaving it more vulnerable to movement, weight, and moisture. Often, this same soil is used as fill soil to fill the space around your foundation after it’s complete. If the soil isn’t packed well enough, it can compress under the weight of your home, causing your foundation to settle.
Wetting and Softening Soil
Heavy rains, flooding, poor draining, and damaged plumbing all introduce excess water into the soil. When this happens, soil softens and expands dramatically. That weakens the soil, reducing its ability to support the weight above it, causing your foundation to shift and settle.