No home foundation is without its risk factors for damages. However, several things specific to the Raleigh area can be more problematic for the structural integrity of your house.
North Carolina has a distinct section of exotic soil, commonly referred to as the Carolina terrane and the Triassic basin. These areas are known for their high instance of clay. The basin encompasses Durham, Chapel Hill, Cary, Garner, Apex, and many other surrounding cities. It also includes a portion of Raleigh, but the rest of the city and much of the nearby area has a high concentration of red clay in the soil as well.
Clay makes soil expansive, which means it more readily absorbs water and expands to take up more volume when it gets wet. This is problematic for foundations because expanding soil puts additional strain on your crawlspace or basement walls. Since concrete cannot flex with earth movement, it tends to crack under the pressure. Depending on where the stress is applied, a foundation crack can lead to structural instability and even potential collapse.
Expansive soil is also dangerous because it presents issues with water intrusion. As it expands from runoff or groundwater, it pushes against your foundation and holds the moisture there. Water from the soil can wick through the porous concrete or seep through natural settling cracks, creating a water or moisture problem and the resulting damage under your home.
Expansive soil is one of the most common causes of foundation damage, and unfortunately, Raleigh has an abundance of expansive red clay.
Above-Average Rainfall & Drought
Raleigh experiences over 45 inches of rain each year, which is about 50% higher than the national average.
Rain poses a threat to foundations for two primary reasons. First, runoff that soaks into the ground around your home can easily seep through cracks in your concrete. It can drip into your basement or crawlspace, causing direct water damage and serving to increase humidity. Second, it can soak directly into concrete and evaporate into the area under your home, increasing humidity and leaving the space prone to mold or mildew growth.
Excessive runoff can be detrimental for foundations in any area, but the danger is compounded in Raleigh because of the city’s expansive soil.
Despite having an above-average annual rainfall, Raleigh also experiences drought more regularly than many other places in the U.S. Drought can mean damage specifically for foundations supported by expansive soils.
The clay soil in Raleigh not only expands when it gets wet but it shrinks when it dries. During a period of drought, the ground around your home can shrink away from your concrete, potentially leaving portions of your foundation unsupported. This places undue stress on the concrete and can create cracks or sinking portions of the foundation.
Multi-level foundations, including partial basements, are more common in Raleigh and the surrounding cities than they are in many other parts of America. They increase your living space along with your home’s value.
The potential issue with them is that they rely on two different levels of soil to support your home. Since the ground can settle at different rates depending on depth, these types of split foundations leave your structure open to differential settling.
Differential settling can be a severe issue for foundations if the concrete loses the support it needs to hold up your home. Sections may move at different rates, leading to cracks and structural integrity loss in some cases.
High, Year-Round Humidity
Raleigh, along with much of North Carolina, experiences relatively high humidity levels year-round. Since basements and crawlspaces naturally have humidity problems, Raleigh homeowners typically experience more of a risk of elevated humidity under their houses, given the climate in the area.
Whether moisture comes in through vents, foundation cracks, windows, or directly through the concrete, high humidity levels lend themselves to mold growth. Mold thrives in dark, moist conditions, so humid basements quickly become breeding grounds for spores if the air is conditioned and dehumidifier.
Mold can damage the construction material on which it grows, leaving crumbling concrete or rotted floor joists in its wake. It can also make its way up to your living space in a process called the stack effect. It can trigger allergic reactions and respiratory problems for those living in your home.
In addition to damaging your property, high humidity under your home can also affect the comfort level of your living space. It can seep into your other floors and make it feel colder in the winter and hotter in the summer.