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The Best Types of Soil for Building Foundations
Know your soils to keep your home stable
Photo: Iriana Shiyan/ Adobe Stock
Photo: Iriana Shiyan/ Adobe Stock
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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.
| Pros | Cons |
|---|---|
| Drought-resistant | Difficult to work with when wet |
| Holds water well | Can shrink and expand |
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.
| Pros | Cons |
|---|---|
| Stable | Absorbs heat quickly |
| Durable | Prone to sinking |
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.
| Pros | Cons |
|---|---|
| Very stable | Can be tricky to level |
| Strong |
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.
| Pros | Cons |
|---|---|
| Stable | Presence of undecomposed materials |
| Handles moisture well |
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.
| Pros | Cons |
|---|---|
| Easy to replace | Doesn’t hold moisture well |
| Prone to shifting |
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.
| Pros | Cons |
|---|---|
| Easy to replace | Doesn’t drain well |
| Poor support |
Best For: Concrete piers
Why Considering Soil Type Before Construction Is Important
Photo: Lev / adobe stock
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.
Pro Tip
"The type of soil your home sits on is crucial for foundation stability. Clay soils expand and contract with moisture changes, which can lead to foundation movement. Sandy or well-drained soils are generally more stable. If the soil isn’t ideal, you might need to take extra measures like soil stabilization or proper drainage systems to prevent shifting and settling."
— Tim O'Shea, The Build Pros
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