Soil Types and Foundation Systems
The soil type where you are planning to build a home can have a dramatic impact on your project. Every house has a foundation which must be built skillfully and safely so it will endure, because as we all know…you can’t build a solid structure on a weak foundation.
The materials that make up this building block are as critical to its success as the process of its construction, and part of the material is the soil that supports the foundation. Every soil type has unique properties that can affect a foundation’s stability and integrity of your home for years to come.
If you aren’t sure of the soil type in the construction area, you can consult local geological survey experts before building. An experienced engineer can usually determine the texture of soil material fairly accurately by the visual method as well as by feeling the soil.
This post offers some advice on how to distinguish various soil types:
THE SQUEEZE TEST
To do this test, be sure your soil is damp, but not soaking wet. Grab a small handful of the soil in your hand. Rub some of the soil between your fingers. If it feels gritty, it’s mostly sand. If it feels slick and slimy, it’s mostly clay.
THE RIBBON TEST
Take a handful of damp soil and make a ribbon by rolling the soil between your hands.
If you can form a ribbon and hold it vertically without it breaking, you have mostly clay soil. If you can make a ribbon, but it breaks off when you try to hold it up, you probably have somewhere between 25 and 50 percent clay in your soil. If you can’t make a ribbon at all, chances are your soil is more than half sand.
See more here: Urban Farmer: How To Determine Your Soil Type
In the above article, they offer a third method that is a little more scientifically based but in general, your soil type will be fairly obvious once you start digging in.
One of the worst types of soil for any foundation to be built on is clay, also known as expansive soil. Depending on how much moisture is in the ground, expansive clay soil with experience changes in volume of up to 30% or more.
Sometimes called shrink-swell soil, during periods of high moisture it will swell, which can cause lifting of a structure. Once the soil dries out, it will shrink and cause the building to settle.
This can cause problems not only with the foundation, but the walls and ceiling can shift, bow, and crack causing extensive damage, which is why soil types and foundation systems are studied so extensively.
In Colorado, this type of soil is a real problem for building contractors. It is imperative that a geotechnical engineer is involved to access that the proper foundation system is constructed. In the following video, the contractor explains why they used a pier and beam foundation:
As he mentioned, because that home is being built in the south where there is no frost line or code regulating that it be a full in-ground foundation.
Types and Costs of Foundations
The cost of any foundation is substantial, but because of the importance of this piece of the puzzle, you don’t want to skimp on getting the right foundation for your soil type. The typical range nationwide is from $4,000 to $12,000.
If you choose to put in a crawl space or basement, then your price goes up considerably. For a crawl space, the cost is generally $7 per square foot and with a basement, it is $10 to $25 per square foot. This post offers more on the expenses included in foundation work: