Quick answer
Soil erosion around foundations is the loss of soil from beside or beneath a house when moving water, such as roof runoff or flood flow, carries it away, leaving walls and footings with less cover and less support.
It ranges from a shallow gully under a downspout to scour that undermines a footing in a flood. The cause is nearly always water that is not led away from the house.
Quick facts
The key facts about Soil Erosion Around Foundations, with sources:
- Plants as protection
- Illinois Extension calls plants the best erosion control 1
- Code grade rule
- Lots graded to drain away from walls; not fewer than 6 inches of fall in the first 10 feet 2
- Hard surfaces near the wall
- Impervious surfaces within 10 feet slope at least 2 percent away from the building 2
- Flood scour
- Shallow foundations can be undermined by scour and erosion; deep foundations naturally resist it 3
- Repair path for undermined footings
- Geotechnical engineer checks soil, structural engineer designs underpinning 3
Key takeaways
- Erosion is water moving soil. Fix the water and the erosion usually slows.
- Splash under a downspout, a gully along the wall and a flood scour hole are three versions of the same process.
- Plants are the best erosion control, according to Illinois Extension. Bare soil beside a wall loses out.
- The model residential code asks lots to be graded to drain away from foundation walls and sets a minimum fall near the house.
- Undermined footings are an engineering problem. A geotechnical engineer checks the soil and a structural engineer designs any underpinning.
What soil erosion around a foundation is
Water is a strong mover of soil. Rain falling from a roof lands in a concentrated spot.
Runoff from a yard or a driveway picks up speed as it flows toward a low area.
If that flow reaches the foundation, it can carry soil away from the wall, from a footing or from under a slab edge.
General information, not a diagnosis of your house. The result is less soil cover on the footing, a trench along the wall that fills with more water, and less side support for the foundation.
In a flood, fast water can do the same thing to shallow foundations at larger scale. FEMA says shallow foundations are vulnerable to moving floodwaters and can be undermined by scour and erosion 3.
Erosion is different from settlement. In erosion, soil leaves the site or moves away. In settlement, soil stays but compresses. Read foundation settlement for the second case. Both can leave a foundation with less support, and a house can have both.
Erosion vs. soil settling
If the dirt beside the wall is gone, think erosion. If the dirt is still there but has sunk, think poor compaction or settling. The fixes differ, and a licensed engineer can tell which applies when the cause is unclear.
How erosion develops beside a house
A typical sequence, built from the extension and FEMA descriptions:
- Water arrives in one place: A downspout with no extension or a gutter that overflows drops roof water at the wall. Colorado State Extension advises keeping downspout extensions in place 4.
- Bare soil loses grains: Rain hitting bare soil dislodges particles. Illinois Extension notes that plants protect soil and that bare ground is exposed 1.
- Flow picks up speed: On a slope or along the wall, runoff concentrates in a channel and carries soil downhill.
- A trench forms: The channel deepens beside the foundation and more water collects there.
- Support is reduced: Soil cover over the footing thins, and in severe cases the soil under it is undermined 3.
- Movement may follow: Reduced support can show up as cracks, tilt or sticking doors, which are clues for an engineer to read.
House with ground sloping away from the wall, a gutter downspout and an extension carrying roof water away from the foundation. A dashed line shows the wrong slope toward the house for comparison.
Illustrative drawing of surface water leaving a house on a good slope and reaching it on a wrong one. It is not to scale and not a design for any house.
Common forms of erosion around a house
| Form | What you see | Usual water source |
|---|---|---|
| Splash erosion | A bare dip or a bare ring under a downspout or eave | Roof runoff striking bare soil 1 |
| Surface channel | A shallow gully along a wall or down a slope | Concentrated runoff from the yard or paving |
| Washout under paving or a slab edge | A gap or void where soil has left | Water entering at an edge or joint |
| Gully in a graded slope | A deep cut in a slope near the house | Unprotected slope with fast runoff |
| Flood scour | Soil removed from around and under shallow footings | Moving floodwater 3 |
Local rules on discharge apply
Where you send water can affect neighbors and may be limited by local rules on drainage and discharge. Check with your building or public works department before regrading or adding drains.
Example: reading the grade rule against a sample yard
An example with invented measurements checked against the model code’s fall rule. IRC R401.3 asks for a fall of not fewer than 6 inches within the first 10 feet from the wall 2.
| Yard | Fall in first 10 feet | Meets the 6-inch rule? | What it suggests |
|---|---|---|---|
| A | 8 inches | Yes | Surface water should leave the wall; check the downspouts |
| B | 3 inches | No | Water may linger near the wall; regrading or a swale may be needed 2 |
| C | Slopes toward the wall | No | A reverse slope sends water to the foundation; seek advice |
| D | Barrier prevents 6 inches | Code allows drains or swales | The code allows drains or swales where barriers block the fall 2 |
These measurements are invented. To check your own, run a long straight board and a level out from the wall and measure the drop. Do not dig to do it.
Where erosion shows up on a lot
Look first at roof drip lines, downspout outlets and gutter corners. Then look at low spots along walls, steps, window wells and the edges of patios and driveways. Slopes that run toward the house, and slopes above a wall, also concentrate flow.
Mulch can hide a problem. Illinois Extension says wood or rock mulch and organic ground cover do not compact well, and that removing them exposes the actual soil surface before regrading 1. A planting bed against the foundation may be sitting over a washout.
In flood-prone areas, erosion and scour can remove soil around shallow foundations such as crawl space foundations, stem walls and slab-on-grade foundations 3. Penn State engineers note that a footing drainage system is usually required to minimize lateral loads on foundation walls 6. See foundation drainage for water control around the house.
What controlling erosion gives you, and its limits
What good control does
Where it falls short
- It cannot restore soil already lost under a footing.
- It does not fix settlement, expansive clay or poor original compaction.
- Big slopes and taller retaining walls need an engineer, as Illinois Extension says for walls over four feet 1.
- Regrading near a wall can send water to a neighbor, so local rules matter.
What we cannot tell from a washed-out spot
A hollow beside the wall does not show how much support is missing. A small gully can be only surface loss. A void under a footing can be hidden. Only an engineer’s review, sometimes with a probe or test pit done safely, can tell.
A crack near an eroded spot is not proof that erosion caused it. Cracks come from movement history, moisture, loads, construction details and site conditions. A pattern is a clue, never a diagnosis.
We also cannot say any particular amount of soil loss is safe. The effect depends on the foundation type, how deep it is, the soil and the loads.
What drives the cost of fixing erosion
We print no prices, because fair numbers need dated local quotes. The cost drivers are how much soil is gone, access for machines, whether gutters and downspouts need work, whether drains or swales are needed, plants or stone to protect the surface, permits, and whether any structural repair is involved.
Simple fixes such as downspout extensions and clean gutters sit at one end. Underpinning an undermined footing sits at the other and needs engineering. See the foundation cost guide and the cost calculator for how quotes are built.
How to deal with erosion beside a house, safely
Dealing with erosion stays at the surface and follows extension guidance. Anything deeper belongs to a professional.
- Fix the water first: Clean gutters and add or reconnect downspout extensions so roof water leaves the wall area 4.
- Clear mulch and plants from the washed strip: Illinois Extension says to remove wood or rock mulch so the real soil surface shows 1.
- Add soil in thin layers: Place and pack soil in lifts, and finish with a slope away from the wall. Illinois Extension recommends at least 4 percent 1. See soil compaction.
- Protect the surface: Plant ground cover or add mulch. Illinois Extension says a 2 to 4 inch layer of coarse woodchips helps protect newly planted slopes 1.
- Watch the next storm: See where water goes and adjust.
Stop if you see a void or a moving wall
Do not dig beside a footing, probe under a slab edge or enter a trench or pit. If you see a void under a footing, a bowing wall or standing water with electrical or gas hazards, step back and call a licensed engineer.
Keeping soil in place year after year
- Clear gutters in spring and fall, and after big storms.
- Check downspout extensions and splash blocks, and reattach any that have moved.
- Walk the house after heavy rain and look for new channels, ponding and bare patches.
- Keep ground cover or mulch on bare areas near the wall. Illinois Extension notes layered plantings slow rainfall so it soaks in gradually 1.
- Keep about 18 inches of foundation wall exposed above soil where possible, and avoid piling soil against siding, as Illinois Extension advises 1.
The drainage and grading guide goes deeper on slopes and water paths.
Warning signs and when to call a structural engineer
Erosion matters most when it reaches the footing. Call a licensed structural or geotechnical engineer when you see:
- Soil washed out so that a footing or the base of a wall is visible or hollow beneath.
- New cracks, widening cracks or a wall that bows or leans near an eroded spot.
- Doors and windows that stick along with new cracks.
- A slab edge or patio that has dropped over a void.
- Repeated flooding or fast flow along the foundation.
- Any safety doubt.
FEMA says to consult a geotechnical engineer to find whether stronger soils are present, and a structural engineer to design underpinning if soil strength is adequate 3. See the structural engineer guide.
What the model code says about drainage and erosion
IRC R401.3 says surface drainage shall be diverted to a storm sewer conveyance or other approved collection point that does not create a hazard, and that lots shall be graded to drain surface water away from foundation walls with a fall of not fewer than 6 inches within the first 10 feet.
Where barriers prevent it, drains or swales shall be built, and impervious surfaces within 10 feet of the foundation slope not less than 2 percent away from the building 2.
Seattle’s R401.5 is a local amendment, not model IRC text. It requires protection of adjoining property during construction, including control of water runoff and erosion during construction or demolition, and sets limits on the slopes of altered grade 2. Other cities may have different rules.
These sections are quoted from Seattle’s 2021 residential code, which reproduces the 2021 IRC with local amendments. Editions and local drainage rules vary, so check what your jurisdiction adopted.
Erosion vs. other reasons soil goes missing near a wall
| Cause | What happens to the soil | Where to read more |
|---|---|---|
| Erosion | Water carries soil away 1 | This page |
| Settling or poor compaction | Soil stays but sinks 1 | Fill soil and foundation settlement |
| Soil shrinkage in drought | Soil pulls away from the wall 5 | Expansive clay soil |
| Groundwater piping or leaks | Water moves fine soil underground | Plumbing leaks and foundation damage |
| Negative grade | Water runs toward the house | Grading around a foundation |
Common myths about erosion near foundations
- Myth Erosion only happens on steep land.
- Reality Roof runoff on flat bare ground can erode a strip beside a wall 1.
- Myth Piling soil against the wall fixes the washout.
- Reality Soil piled against siding invites other problems, and new soil must be placed in packed lifts and graded away 1.
- Myth Gravel alone stops erosion.
- Reality It can help the surface, but water control and slope come first.
- Myth Deep foundations never erode.
- Reality FEMA says deep foundations naturally resist scour and erosion, but the rest of the site can still erode 3.
- Myth A tall retaining wall is a DIY job.
- Reality Illinois Extension says walls over four feet often need an engineer 1.
Where climate and flood risk change the problem
Erosion risk follows rainfall intensity, slope, soil and flood exposure. Heavy-rain and flood-prone areas see more scour, and FEMA’s handbook is written for hurricane and flood zones 3.
Dry regions with clay soils face a different issue, soil shrinking away from walls, as NDSU and Colorado State describe 54. Drainage discharge rules also differ by city. Ask your building department what applies before regrading.
When erosion matters, and what to do next
Erosion matters once soil is gone from a spot that supports the house. Start with the cheapest and safest facts: where the water comes from and where it goes. Gutters, downspouts and a slope away from the wall fix most surface erosion.
If a footing is exposed, a void is under a slab or cracks are changing, call an engineer. The water intrusion tool helps you sort out where water is entering.
- If Bare dip under a downspout or along the wall
- Then Fix the downspout and gutters, then regrade in packed lifts
- If Footing or wall base exposed, or a void under a slab edge
- Then Stop, keep clear and call a licensed engineer
- If New cracks near the eroded spot
- Then Record them with dated photos and ask an engineer to read them
Questions about Soil Erosion Around Foundations
What causes soil erosion around a foundation?
Moving water: roof runoff with no downspout extension, surface flow along a wall, and flood flow. Bare soil is the most exposed. Illinois Extension calls plants the best erosion control, and good grading and gutters keep water from reaching the wall at all.
Can erosion damage a foundation?
It can if enough soil is lost to reduce support. FEMA says shallow foundations can be undermined by scour and erosion. A small surface gully is usually just a drainage fix, but exposed or hollow footings call for an engineer.
How do I stop soil washing out next to my house?
Fix the water first with clean gutters and downspout extensions, then clear mulch, add soil in thin packed layers, slope it away from the wall and plant or mulch the surface. Do not dig beside the footing. Local discharge rules may apply.
What slope should the ground have next to my foundation?
The model residential code asks for a fall of not fewer than 6 inches within the first 10 feet where space allows, and Illinois Extension recommends at least 4 percent. Your jurisdiction’s adopted code and any amendments apply.
Is a gap between soil and my foundation wall erosion?
It may be erosion, settling or soil shrinking in dry weather. NDSU says clay soil can pull away from a basement wall in drought. Do not fill the gap with soil, since wet soil expands. Find the cause first, and ask an engineer if cracks appear.
Do I need a retaining wall to stop erosion?
Not always. Plants, grading and drainage solve many cases. Illinois Extension says walls under four feet can usually be built by a landscape contractor and taller ones often need an engineer. A wall near a foundation should be designed, not guessed.
What is foundation scour?
Scour is erosion by moving water that removes soil from around and under a foundation, most often in floods. FEMA says shallow foundations are vulnerable to it and deep foundations naturally resist it. Repair of an undermined footing needs a geotechnical and a structural engineer.
Are downspout extensions really worth it?
Yes. Colorado State Extension tells homeowners not to remove downspout extensions, because they carry roof water away from the foundation. Illinois Extension also pairs good grading with water control as the first fix for water at the wall.
When should I call an engineer about erosion?
Call when a footing or the base of a wall is exposed, soil is missing under a slab edge, cracks are new or growing, or a wall bows. Surface washouts can be handled with drainage and regrading, but anything touching support is engineering work.
Sources
- University of Illinois Extension, Landscape Drainage for Homeowners (February 12, 2020), retrieved .
- City of Seattle, 2021 Seattle Residential Code, Chapter 4 Foundations (2021 IRC text with Seattle amendments), retrieved .
- FEMA, Hurricane and Flood Mitigation Handbook for Public Facilities, Fact Sheet 3.1: Foundations (March 2022), retrieved .
- Colorado State University Extension, PlantTalk Colorado 1617: Expansive Soils, retrieved .
- NDSU Extension, Ken Hellevang, Dry Soil May Cause Building Problems (June 30, 2017), retrieved .
- Penn State, Singh and Scanlon, Concrete in Residential Construction, 1st Residential Building Design and Construction Conference (2013), retrieved .
Expert review
Written by the HyreFoundation Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Grading, mulch, plant and wall-height guidance comes from University of Illinois Extension. Scour, shallow and deep foundation facts and the engineer sequence come from FEMA Fact Sheet 3.1.
Code text comes from Seattle’s 2021 residential code, which reproduces the 2021 IRC with city amendments. Soil shrinkage and downspout advice come from NDSU and Colorado State extension. Yard measurements in the example are invented and labeled. No prices.
Suggest a correction. We fix errors and say what changed.