Soil is an essential component in the construction and stability of a house that is often underappreciated by homeowners and homebuyers. Serious structural damage to a house can occur if the soil expands, contracts or slides.
Expansive Clay Soils
In Colorado expansive clay soils are known to cause damage to homes and commercial property. Expansive soil expands and contracts due to changes in the moisture content of the soil, causing structural problems through differential movement of the structure. If the moisture content and or soil type differs at various locations under the foundation of a home, localized or non-uniform movement may occur and can cause damage to the foundation and framing, evidenced by cracking of the slab or foundation, cracking in the exterior or interior wall covering, uneven floors and/or misaligned doors and windows. This type of movement can be associated with slab on grade construction and in structures with basements and crawlspaces.
Expansive soils can also apply horizontal pressure to foundation walls. If the foundation walls do not have sufficient strength, cracking, bowing or movement of the wall may occur and serious structural damage to, or failure of, the wall may occur.
Prior to building a home, the builder must obtain a soil test of the specific site to ensure the soils are stable or to determine the approximate effect the soils will have on the home. Information on the soils can ensure that the foundation is designed to withstand the effects of the existing soil conditions. If the soils conditions are not property considered in the design and construction of a home, the home may be destined to fail.
Floor Systems: In an effort to account to the effects of expansive soils, builders will often install a "floating slab" or a "structural" floor system for the basement floor. The "floating" floor system is a concrete floor, the "structural" floor can be wood or concrete. The builder may decide to employ a structural floor system, dependent on recommendations from an engineer based on the site and soil conditions. The structural floor is by definition, a "structural" element. The floor is suspended from the concrete foundation wall, and supported by a system of beams and floor joists. The floor is designed to achieve "isolation" from the normal movement of soil material underneath by means of a voided area directly underneath. Failure to design such a system appropriately, or the failure to construct such a floor system as designed, can lead to serious damage to the home.
For structures affected by expansive soils, further movement may be able to be prevented by providing additional strength and support to the foundation. This may include various methods of underpinning to prevent vertical movement and/or sliding and/or reinforcing of the foundation walls to withstand lateral pressure. Such modifications and repairs can be expensive.