Originally Published: October 9, 2015 6 a.m.
We are looking at a lot in unincorporated Yavapai County and our realtor told us we need a soils report. Why?
A: In Arizona our biggest worry is our soil, which can cause problems with the foundations of our homes. Fortunately, most problems caused by bad soil can be repaired. A lot of soil-related problems arise because homeowners assume living in a dry climate means the soil is dry, sandy and stable, so they do not think twice about planting and watering near the house. In many areas of the state, the soil contains a high percentage of clay, meaning it is neither sandy nor stable. In fact, clay-based soil expands when it gets wet and shrinks when it dries. Soil is moisture-sensitive, and as long as it is dry, there is no problem. Water changes everything. As soon as moisture fluctuates, during a monsoon storm or if you plant a yard full of thirsty greenery, the problems begin. When clay-rich soil comes in contact with water, it expands, causing the soil particles to push upward. If that happens right under your house, it can damage your foundation. Expansive soil is among the most expensive geologic hazards and causes $300 million a year in damage to homes.
Building codes do not assure long-term performance (settlement or heave values within industry standards) of the fills, footings and floors. We can only assume that you all want to build a good, well-performing building.
Due to often substandard soils conditions, Geotechnical reports are required on lots in the unincorporated areas of Yavapai County upon applying for a permit to construct a house or addition over 400 square feet in size. The report is prepared by a licensed geotechnical engineer and will address the conditions of the soil where development is proposed. This information is imperative when considering the foundation design of the structure, as depending on conditions, significant foundation engineering may need to be performed.
All too often, substandard soils have been discovered upon inspection of foundation footings, requiring a builder to cease construction until the soils issue can be mitigated. Typically this result in unexpected costs to the builder and homeowner and results in unnecessary delays in the project. Failure to mitigate substandard soils can result in complete failure of a structure. Buyers of vacant lands in the unincorporated areas of Yavapai County should be encouraged to investigate soils conditions upon considering purchase of property in order to adequately project development costs.
It would be beneficial to anyone building a new home to investigate, sample and test the soils prior to permit and construction to determine their physical and engineering characteristics of the soil. You should know what you are building on!
Problems associated with expansive soils include: foundation cracks, cracks in floor slabs and walls, jammed doors and windows, ruptured pipes and cracks in sidewalks and roads. Not all soil is Arizona is expansive. Some is collapsible, which means it is loose and dry, and will collapse and compact when it gets wet. This kind of soil can cause your home to settle rather than heave, but the symptoms are similar to the heaving brought on by expansive soils, cracked foundations, floors and walls.
Recently a 4-year-old home started to heave such that there were more than three inches of differential floor movement from one side of the house to the other. Subsequent remediation revealed that the soils consisted of a medium to high plasticity clay soil. The maximum soil movement occurred under the bearing footings on the southerly side of the house where exposure to rain and snow water was the highest.
Remediation efforts consisted of: installation of helical piers under house footings, removal of the entire floor slab, addition of temporary support of interior non-load bearing walls, removal of two feet of the clay soils from within the entire building footprint, removal of 8 inches of clay soil from below the base of the foundations, installation of a low-density foam between the clay soil and the footing base, installation of non-expansive floor fill, and replacement of concrete floors. Cost to repair: $250,000 as compared to a soil investigation report at approximately $1,600 if one had been performed prior to building on the lot.
As the population continues to move into the outer reaches of the communities, many times project sites become more and more marginal. These sites can be built upon, but it is critically important to address the long-term performance of your home on the lot and build to a "higher" industry standard by obtaining a Geotechnical Engineering Report on your lot before you build.
A soil engineering report will present a picture of what the intended project will consist of; recommendations to be used by a structural engineering for footing depth, width, bearing pressure, estimated settlements, heave potential, etc. A soils report also presents to civil engineers site grading requirements, minimum ground slopes, minimum permanent cut and fill, etc. The report contains a description of the site and soil conditions so the builder will know what they will have to contend with.
In short, a soil report is the "how to design and build recipe for the first structure" that goes on the site. If followed, it will result in a successful, long-term performance of the home.
Remember to tune in to YCCA's Hammer Time twice each weekend Saturday and Sunday morning 7 a.m. on KQNA 1130 AM/99.9 FM or the web kqna.com. Listen to Sandy and Mike talk about the construction industry and meet your local community partners and contractors.
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