Why Soil Type Matters for Foundations

All homes and buildings have a foundation. The type of foundation that is chosen is important to the safety and stability of the home or building, but there is also something else to take into consideration: the type of soil supporting the foundation. The soil and the foundation work together to support a building. Here’s what you need to know about why soil type matters for foundation.

Why does soil type matter?

You can have the best, most sturdy foundation, but if the soil isn’t strong enough to support it, it won’t be able to do its job effectively. Each type of soil has its pros, cons, and special requirements. These can depend on where you live, the size of the building, and the properties within the soil itself.

Different Types of Soils

As mentioned there are different types of soils. Clay soils are made up of small particles, which means they store water well. Clay soil will expand when moist and shrink when dry. This is not ideal for all foundations as the constant shifting of soil will cause pressure to the foundation. The foundation will move up, down, even side to side, and in time be damaged. Sand and gravel soils have large particles. Large particles mean the soil will not hold as much moisture, which is good. When this type of soil is moist and compacted well, it holds together well and supports the foundation as needed.

Unfortunately, when moist, these larger particles can lose their friction, which allows them to be washed away leaving gaps in the soil beneath the foundation. A soil that contains more sand and/or gravel and is compacted well will help the foundation to stay stable. Another type of soil is loam. Loam soil is ideal because it contains clay, silt, and sand. This combination allows for more balanced moisture, which is more suitable for helping to support a foundation. Rock soils, which include limestone, granite, shale, or sandstone, have a high bearing capacity.

Choosing a Foundation

Before you choose a foundation, you need to know what kind of soil it will be placed over. Failure to determine this can result in choosing a foundation that isn’t compatible. This will cause not only foundation damage, but to the home or building as well. If the soil is weak or expansive, such as clay or peat, you will want to choose a foundation with reinforced concrete. If working with a peat soil, a pad and beam foundation is a good choice for a smaller project. A larger project should use a raft foundation. A soft clay soil is more compatible with a raft foundation, wide strip footing, and for smaller projects a pier and beam foundation (that goes down to firm strata).

The type of soil used to help support the foundation of a home or building is more important than you might think. Structural failures can often be linked to soil and foundation chosen for that type of soil. Knowing the type of soil you’re dealing with gives you the upper hand in choosing the perfect foundation.


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