Washington, D.C residents deal with foundation problems regularly, primarily due to the soil composition and climate in the area. We’ll talk about each underlying cause of foundation damage in D.C. below and how each contributes to problems with your under-home area.
The soil on which a home is constructed plays a significant role in the stability and persisting integrity of the structure. Much of Washington, D.C. is built on expansive soil, meaning it has a high concentration of clay particles. Clay can pose a severe risk for home foundations for several reasons.
First, clay particles absorb water in more significant volumes than typical dirt and retain it for more extended periods. Several soil associations in Washington are considered poor bases for construction, and many other soil types in the city are far less than ideal.
The inadequate drainage of these soils means they hold runoff against your concrete for days or weeks following rainfall, exposing your home to water intrusion and moisture build-up.
Second, clay soil expands when it gets wet, as the tiny particles attract water through capillary action and swell as they accumulate moisture. Expanding soil grows laterally and upward, placing undue stress on your basement walls and concrete slab.
Concrete is rigid and cannot flex in response to the hydrostatic pressure, so it typically cracks to relieve the stress. This leaves you with a structurally compromised foundation.
Lastly, expansive clay soil shrinks when it loses moisture. After the runoff suspended in the ground around your house drains or evaporates, the soil shrinks and can provide less support to your concrete. This process is typical in most areas, but the clay concentration in the soil can cause the drying and shrinking to occur at varying rates under and around your home.
The uneven shrinking around your home is called differential settling, which finds sections of your foundation losing support from dry soil while others remain braced by moist soil. This can quickly lead to structural damage that compromises the integrity of your foundation.
Expansive soil is hazardous to foundations, but the danger is only present when moisture changes occur in the soil. Unfortunately, Washington, D.C. experiences above-average and frequent rainfall, contributing to varying moisture levels in the ground.
The city sees approximately 43 inches of rain annually, which is nearly 30% higher than the national average. The above-average rainfall leaves the soil saturated more often, increasing the chances of it expanding to dangerous levels and extending the interaction time between moisture and your concrete.
Additionally, the rain falls about two days a week, creating an unideal wet-dry cycle for the soil. The rapid swelling and shrinking of the earth leave home foundations at higher risk of uneven settling.
The frost depth in Washington, D.C. – which is the depth to which the water in the ground freezes – is just 2-1/2 feet. For homes built on slab-on-grade foundations, this means that the ground will likely freeze below the lowest part of the cement.
When the water in the ground freezes, it expands and places additional pressure on your concrete. The upward force of the freezing water can heave portions of your foundation, leaving you with structural damage.
Homeowners with crawlspaces, basements, and D.C.’s more common English basement are at less risk of frost heave, but the expanding water suspended in the clay-rich soil can have some dangerous consequences for concrete block walls.
D.C. residents are, unfortunately, very aware of the risk of flooding. There are multiple potential causes for floods in the city, including heavy rainfall from storms, snowmelt, and flash flooding. Tidal rivers are also commonly to blame, especially the Potomac and Anacostia Rivers, which can overflow during rainfall or with rising tides.
Flooding can not only cause significant water damage, but it contributes to the already-present problems with expansive soil.
Floods saturate the ground completely, increasing the volume to which it swells and leaving your foundation prone to leaking moisture intrusion.
Lastly, earthquakes can contribute to foundation problems in D.C. The area itself isn’t considered a seismic zone, but there are several zones nearby that can cause ground shaking in the city.
Even the small earth movements that are more common in Washington can wreak havoc on your home’s foundation, contributing to differential settling over time and causing shifts in the soil that put excessive pressure on your concrete.