Erosion beneath a home’s foundation is a critical structural red flag. It means that the soil supporting the structure has been displaced, typically by water, leaving parts of the foundation unsupported or under-supported. This can result in cracking, settlement, tilting, or even structural failure if left unaddressed. This article explores why erosion below a foundation happens, how to identify it, and what actions homeowners should take.
What Is Foundation Erosion?
Foundation erosion refers to the removal of soil or sediment beneath or around the footings or slab of a home. This void or gap compromises the load-bearing capacity of the soil, potentially destabilizing the entire structure.
Common Causes of Erosion Below Foundations
Poor Site Drainage
Downspouts, gutters, or landscaping that direct water toward the home instead of away from it can cause water to wash out soil below the foundation.
Broken or Leaking Pipes
Sewer, water, or irrigation line leaks near or under the foundation can erode soil slowly over time.
Improper Grading
If the yard slopes toward the home instead of away from it, runoff during storms or irrigation events can flow directly under the foundation.
High Water Table or Flooding
In some areas, fluctuating groundwater levels or storm surges can wash out soil under slab-on-grade or raised foundations.
Animal Activity
In rare cases, burrowing animals like gophers or ground squirrels can cause localized erosion near foundation piers or footings.
Signs That Erosion Is Affecting the Foundation
Even if the erosion isn’t visible, some of the following signs may indicate a problem:
Visible gaps beneath footings or piers
Cracking in foundation walls, floors, or exterior stucco
Sagging floors or uneven interior surfaces
Moisture intrusion in the crawlspace or basement
Drainage trenches or ruts leading toward the foundation
Vegetation loss or sinkholes near foundation edges
Risks of Unaddressed Foundation Erosion
Foundation Settlement: Portions of the home can sink unevenly, leading to structural distortion.
Wall Cracking and Door Misalignment: Uneven load paths often cause drywall and framing shifts.
Structural Failure: In extreme cases, if the foundation loses support, it may fail—leading to catastrophic consequences.
Decreased Property Value: Active erosion is a major concern for buyers, insurers, and appraisers.
Moisture and Pest Entry: Gaps under the home can allow water, air, and pests to enter.
Recommended Actions and Repairs
1. Professional Evaluation
Hire a structural engineer or geotechnical engineer to assess the extent of erosion and design an appropriate remediation plan. It’s critical to understand why the erosion occurred before taking corrective steps.
2. Improve Drainage Immediately
Extend downspouts and install splash blocks or drainpipes to redirect water far away from the home.
Regrade the surrounding soil to create a minimum 6-inch slope over the first 10 feet away from the foundation.
Install French drains or surface drains to intercept runoff.
3. Repair the Foundation (if needed)
Depending on the extent of damage:
Pressure grouting (slab jacking) may be used to fill voids beneath concrete slabs.
Helical piers or push piers can be installed to transfer the home’s load to deeper, stable soil layers.
New concrete footers or underpinning may be necessary in crawlspace homes.
4. Fill Voids and Stabilize Soil
Soil stabilization may involve injecting polyurethane foam, grout, or compacted soil into eroded areas to fill gaps and restore support.
Erosion control mats, retaining walls, or vegetative stabilization may be used for slope areas.
5. Ongoing Monitoring
After repairs, regularly monitor:
Soil moisture near the home
Structural movement (with elevation readings if available)
Drainage performance during heavy rains
Conclusion
Erosion below a home’s foundation is not just a drainage problem—it’s a structural hazard. Even small voids or washouts can undermine the integrity of the building over time. Fortunately, with early detection, proper drainage improvements, and structural reinforcement where needed, homeowners can correct the problem and protect their investment. If this condition is observed during an inspection, it warrants prompt attention by both structural and drainage professionals.