The Best Types of Soil for Building Foundations

That home you cherish sits on soil, but not all soil is the same. Some soils are strong enough to support a skyscraper, while others can't even support a person’s weight. 

Here are a few of the most common soil types and how they affect a home’s foundation.

1. Clay Soil

Clay is an expansive soil. When exposed to moisture, clay can greatly expand, but it will shrink significantly when it’s dry. A drought impacts a home’s foundation significantly if the house sits on clay.

These extreme changes can cause a foundation to shift and eventually crack, making clay a less appealing foundation soil.

Best For: Drilled pier and slab-on-grade foundations

2. Sand and Gravel Soil

Sand containing gravel has large particles that drain easily. When mixed with gravel and other materials, sand does not retain water. This means there is less risk for the building to shift around. Compacted sand and gravel offer even more stability and are a great option to build a foundation.

Best For: Helical piers

3. Rock Soil

There are many rock types, such as bedrock, sandstone, and limestone.

Rock soil makes for an excellent foundation thanks to its stability, its high bearing capacity, and its resistance to water damage. It’s ideal for supporting residential or commercial buildings.

Best For: Strip, pad, and raft foundations

4. Loam Soil

Loam contains sand, silt, and some clay. Loam has a dark color, soft, dry, and crumbly to the touch.

Loam generally doesn't shift, expand, or shrink. It drastically handles the presence of water very well. It incorporates the best qualities, making it ideal for supporting a foundation.

Best For: Isolated pad footings

5. Peat Soil

Peat is usually dark brown or black, often found in bogs and wetlands. It consists of decaying or organic matter.

Peat may be the worst soil to build a structure on. It is highly compressible and can absorb a lot of water, but it also dries out easily, causing it to shift and move, risking the stability of the foundation.

Best For: Concrete piles and raft foundations

6. Silt Soil

Silt is poor soil for building a foundation due to its poor ability to drain water. This causes silt to shift and expand, which does not provide the building any support and puts it under repeated, long-term stress, causing structural damage or failure.

Best For: Concrete piers

Why Considering Soil Type Before Construction Is Important

The strength and stability of the soil depend on its physical properties. It's important to obtain a soil report, which will help better calculate the soil's bearing capacity. Determining the soil type before starting a project can make the job more efficient.

Failing to pick the best foundation type for the soil can cause immediate or future foundation issues. Even if your house was built using the wrong foundation, it's never too late for a foundation repair. Contact a local foundation contractor to assess the situation and suggest a solution that will protect your house and save you future costly repairs.