The Truth About Expansive Soil

And how it could be the reason you're having foundation problems.

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Straight Talk About Foundation Soils

The soils around your foundation can put a lot of pressure on your foundation walls! The amount of pressure will vary depending on three factor:

  • the types of soil around the home
  • how much moisture is in the soil (hydrostatic pressure)
  • how deep underground the foundation is built

Expansive Soil Can Cause Foundation Problems

Expansive spoil is distinguished by the presence of swelling clay minerals that can absorb a significant amount of water molecules. When expansive soils obtain moisture, they expand or swell up. Likewise, when expansive soils lose moisture, they begin to shrink.
Since foundation walls are designed to support loads from above rather than lateral (sideways) bearings, expanding soil can cause foundation problems.

Hence, when rain or improperly channeled water enters too quickly and oversaturates your backfill soil, that excess water will exert immense pressure against your foundation walls. This is known as hydrostatic pressure.

The Problem with Hydrostatic Pressure

Water is heavy! And it can build up underneath the floor, pushing upwards against your foundation. This is known as hydrostatic pressure and will enter the home through any weak point it can find.
When that pressure bearing down becomes greater than your below ground basement or crawl space walls can handle, the affected walls will begin to crack, bow, and push inwards.
As pressure continues to build over time, what starts as a hairline crack will worsen and can eventually result in extreme wall failure, typically in the form of buckling, shearing, or even complete collapse.
In addition to hydrostatic pressure caused from heavy or steady rains, factors such as expansive clay (which all homes in Georgia reside on) and water thawing too quickly after a winter freeze can also create too much stress on basement walls, causing them to crack, bow, and deteriorate.

Backfilled Soils & Virgin Foundation Soils

When your home was being built, contractors had to dig a big hole in the ground. This was created to make space for your basement. They dug up mounds of the hard-packed earth that were there — some of which may have laid there untouched for hundreds of years beforehand.
As foundation walls and house framing were completed, the empty space around the foundation needed to be filled. Contractors typically backfill foundation walls using some of the excavated soil that was removed to make room for the basement. This is known as the clay bowl effect because a clay bowl is carved out from the virgin soil to make room for the house.
The excavation process breaks up and loosens the soil before it is eventually poured back into its original place (or backfilled). Because of this, backfill soils will always be more permeable, or water-absorbent, than the hard-packed earth beyond. When it rains, the water collects in backfilled soils. That water rushes through the soil and presses down in the form of hydrostatic pressure against foundation walls.

Signs of Expansive Soils

Not sure expansive soil is the source of the problem? There are a number of ways to identify that your home may be having issues directly or indirectly related to expansive soils including:

  • Cracks in your foundation or basement walls
  • Sloping or spongy floors
  • Doors and windows that stick
  • Gaps at the top, bottom, or side doors
  • Drywall or stucco cracks
  • A sagging roof

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