It’s no secret that builders have one chance to properly build a home. However, even the most experienced and conscientious builders can run into foundation issues. Soil movement surrounding a home’s foundation causes more than 80% of structural defects, and framing-related issues cause the remaining 20%. Since a surprising number of all homes in the U.S. will experience structural damage throughout their lifetime, it’s worth understanding why and how that damage occurs.
The Main Causes of Structural Damage
Soil movement beneath a home’s foundation is the leading cause of structural damages. There are two types of soil movement that damages homes: heave from expansive soils and settlement from consideration of fill or native soils. Active soils blanket more than 50% of the country and are responsible for more property damage to homes than floods, earthquakes, hurricanes, and tornadoes combined. The clay in active soils expands when exposed to moisture and shrinks when conditions are dry. With these changes occurring regularly as seasons and drought conditions change, it’s easy to understand why active soils are highly problematic. Industry construction standards suggest that homes should be designed to move no more than half to one inch as they settle. However, swollen soil underneath a home can move an entire house six inches or more, and basements have moved as much as 12 inches. As movement under the home’s foundation is generally not uniform, this can cause serious damage to the structure.
Conversely, consolidation of settlement or native fill soils is the second main cause of structural claims. Fill material needs to be compacted properly to support a home’s foundation in the same way that natural soils typically do. Fill material is generally made up of a composite of soils specified by the geotechnical engineer. If not properly compacted, the weight of the home will compact the material and cause settlement. Failure to follow geotechnical recommendations or improper supervision during fill-soil placement can result in settlement damage. Native soils can be problematic, as well, if footings are underlain by a layer of soft materials at a depth not visible at excavation. Hydro-collapsible soils may also result in settlement, and hydrostatic pressure may base lateral foundation wall damage.
A thorough understanding of the soils on the site is the best way to avoid encountering foundation problems from active soils and fill materials. A geotechnical investigation is one quantitative way for builders to know precisely the types of soil they are dealing with. However, even a thorough geotechnical investigation can miss critical data about a particular plot of land, as one builder in New Mexico experienced.