Soils with high concentrations of expansive clay are common in many parts of the Boulder County and Denver Metro real estate markets. When wet, the clay in these soils can swell to several times their normal volume, creating forces that can easily lift the concrete slabs in driveways and basement floors several inches. In extreme cases, these forces can result in extensive damage to foundations and structures, pushing a foundation wall inward a foot or more.
Builders are now required to test for expansive soils and a wide range of construction practices are used to mitigate the potential effects of expansive soils. Many experts contend that the impact of expansive soils on most homes will have already manifested themselves on homes more than three to five years old. Experienced inspectors are well versed in looking for signs of such damage. An important caveat, however: If you or your neighbors do anything to change the landscaping, or otherwise cause more water to accumulate near the home, you may create new problems. With new homes, you should try to obtain a copy of the builder’s soils report and verify that the builder has followed the engineer’s recommendations on construction practices. Be very cautious if you are considering finishing a basement in a new home, since movement of the basement slabs could be extremely costly. The Colorado Geological Survey (303-866-2611) has several useful publications on expansive soils and construction practices.