You probably don’t spend much time thinking about the dirt under your home in Wake Forest, NC, or a surrounding area in our beautiful state. But that ground is the single most important factor for your home’s long-term health.
Knowing the different types of soil can save you from major headaches and costly foundation repairs down the road. In fact, you can spot trouble before it starts because you understand the types of soil and how they behave.
The ground beneath your house isn’t static. It moves, swells, and shrinks with the seasons. Getting familiar with what you’re dealing with puts you in more control of your biggest investment.
Why the Dirt Under Your House Matters
Your concrete foundation is strong, but it relies completely on the soil supporting it. If the soil is unstable, your foundation will also be unstable. This simple fact is critical for every homeowner to understand.
So, what type of soil is best for a solid foundation? Good construction soil must have excellent load-bearing capacity. This lets it support the immense weight of a house without compressing or sinking over time.
The soil should also handle water well. You need it to drain properly without washing away or causing huge shifts. According to the U.S. Geological Survey, groundwater is always moving and interacting with the Earth, which directly impacts your home.
Man-Moved Soils: A Special Case
Sometimes the soil at a construction site isn’t the original, native dirt. Builders often move earth around to level a property. This relocated material is called fill dirt or backfill.
This creates a big variable for your foundation’s stability. If this fill dirt wasn’t implemented with proper soil compaction, it can cause serious issues. Poor compaction leaves behind air pockets that slowly collapse under your home’s weight.
This process is called settlement, and it leads to sticking doors and windows. You might also see cracks in your drywall or brickwork. This settlement is a slow, quiet problem that can lead to significant structural damage over the years.
An In-Depth Look at Native Types of Foundation Soil
Most homes are built on native soil layers that have been there for thousands of years. These natural soils have very different personalities. Knowing which one you have is the first step in preventing serious foundation issues.
Expansive Clay: The Problem Child
Clay soil is a very common soil type in many parts of the country. It’s made of tiny, fine particles. Its structure allows it to soak up a lot of water.
When clay gets wet, it swells up and expands dramatically. Then, during a dry spell, it shrinks and cracks. This constant cycle of swelling and shrinking creates expansive soil problems and puts tremendous stress on your foundation. This movement can cause your foundation to heave upward or settle downward unevenly.
Expansive soils are a leading cause of foundation damage. The pressure can easily crack concrete slabs and walls, often requiring professional drainage solutions to manage moisture levels.
Sand and Gravel: Usually a Safe Bet
On the other end of the spectrum is soil made of sand and gravel. The particles are much larger and coarser. This means water drains through it very quickly.
This excellent drainage makes sandy or gravelly soil very stable. It doesn’t expand or contract much with changes in moisture. This removes one of the biggest threats to a foundation.
Because it doesn’t shift, it gives consistent support year-round. Compacted sand has a high bearing capacity and is one of the best materials to build on. This is why it’s often used as a base for roads and other structures.
Loam: The “Just Right” Soil
If there were a perfect soil for construction, it would be loam. Loam is a balanced mixture of sand, silt, and clay. It takes the best qualities from each component.
Loam can hold some moisture, which is good for stability. But it also drains well enough to avoid becoming waterlogged. This balance means it doesn’t shift or shrink in any extreme way.
A home built on loam soil is very fortunate. It experiences far less soil-related stress. This translates to fewer structural problems over the life of the home.
Bedrock: The Ultimate Foundation
Bedrock is the layer of solid rock found deep within the Earth. As you can imagine, it’s the most stable material possible. Building directly on bedrock is the gold standard for construction.
It has an extremely high bearing capacity. It won’t shift, settle, or swell no matter the weather. A foundation on bedrock isn’t going anywhere.
But there’s a catch. Bedrock can be located very deep underground. Excavating down to it can be incredibly difficult and expensive, so it’s not a practical option for most residential construction projects.
| Soil Type | Water Drainage | Bearing Capacity | Common Foundation Issues |
|---|---|---|---|
| Expansive Clay | Poor | Variable (Low when wet) | Heaving, settlement, and wall cracks. |
| Sand and Gravel | Excellent | High | Erosion is possible if it’s not contained. |
| Loam | Good | Good | Low risk, very stable. |
| Bedrock | N/A (Solid Rock) | Very High | None, if built upon directly. |
How Do You Know What Soil You Have?
This is probably the question you’re asking yourself right now. How can you find out what kind of ground your house is sitting on? You have a few options for identification.
You can start with some simple observations. Look at the ground in your yard during a very dry period. Do you see large, deep cracks forming? That is a classic sign of clay soil.
Another simple do-it-yourself method is the jar test. Fill a clear jar about halfway with your soil, add water until it’s nearly full, and shake vigorously. Let it settle for a day, and you will see layers form with sand at the bottom, silt in the middle, and clay on top.
For a definitive answer, you’ll need professional soil testing. A foundation repair expert or a structural engineer can evaluate your property and diagnose the soil conditions with accuracy. They can provide a geotechnical report that details the soil composition and its properties.
This report is invaluable for understanding your home’s specific risks. If problem soils are identified, the professional may recommend solutions. These can include drainage improvements or even soil stabilization techniques to improve its load-bearing capacity.
Our Conclusion
That dirt beneath your home is more than just dirt. It’s a complex, active material that directly affects your home’s structural integrity. Being aware of the different types of foundation soil is a powerful tool for any homeowner.
Whether you’re dealing with troublesome clay or stable loam, this knowledge helps you protect your home. Understanding the types of building foundation soil ultimately empowers you to maintain your home’s value for years to come.
