When rain washes soil away from the foundation, you may see exposed slab edge, gullies under downspouts or beds sinking. This is erosion right where you need soil to stay in place and slope away from the house.
The cause is almost always concentrated water: roof runoff with no gutters, a downspout or a valley that dumps a lot of water on one spot.
What you may be seeing
- Exposed slab edge or foundation
- Trenches or gullies under the roof edge
- Holes at downspout outlets
- Mulch and soil washed onto walkways
- Beds sinking along the house
- Soil splashed onto siding
First question: where is the water hitting the ground?
Look up. Erosion directly below a roof edge means no gutter or an overflowing gutter. Erosion at a downspout means it needs an extension or an underground line.
If erosion is under the roof edge
Water sheets off the roof and digs a trench.
Possible causes:
- No gutters
- Overflowing or clogged gutters
- Roof valley concentrating water
If erosion is at a downspout
The downspout outlet is too close or has no splash protection.
Possible causes:
- Missing extension
- Displaced splash block
- Underground line backing up
If erosion follows a slope along the house
Water running along the foundation is carrying soil with it.
Possible causes:
- Grade running along the house instead of away
- Neighbor runoff
- Irrigation runoff
What you can check yourself
Only check these safely and after rain has stopped. Do not dig near marked utilities, and do not go near electrical equipment that is standing in water.
- Watch the roof edge during rain
- Check that gutters and downspouts flow freely
- Measure how much slab is exposed
- Look for soil on walkways after rain
- Check for irrigation spraying the area
Answer 20 quick questions → to get a preliminary drainage assessment.
What a drainage professional may evaluate
- Roof runoff and gutter assessment
- Downspout line testing
- Grade measurements
- Soil restoration and erosion control plan
Most common causes
Missing or overflowing gutters
Roof water hits the soil at the drip line.
Short downspouts
Concentrated discharge at the foundation.
Roof valleys
Two roof planes funnel water to one spot.
Grade along the house
Water runs parallel to the foundation.
Irrigation runoff
Spray hitting the soil and walkways.
Possible solutions
The right fix depends on where the water comes from, where it collects and where it can legally and physically go. These are the solutions most often considered:
Gutters and downspout drainage
Capture roof water and carry it away.
Regrading and soil restoration
Rebuild soil to slope away from the house.
Erosion protection
Rock, mulch or plantings to protect the soil surface.
Surface drains
Collect water before it runs along the foundation.
When to call a drainage professional
- Slab or foundation footing is exposed
- Erosion returns after you fill it
- You see foundation cracks
- There's a valley that dumps heavy water
Frequently asked questions
Should I add dirt around my foundation?
Adding soil to restore the slope away from the house is common. Fix the water source first or it will wash away again, and keep soil below siding and weep holes.
What kind of soil should I use?
A soil that matches or is slightly heavier than the existing soil, compacted and sloped away from the house. Avoid pure sand against the foundation.
Do gutters stop foundation erosion?
Gutters plus downspouts that discharge away from the house solve most roof-caused erosion.
Bottom line
Soil washing away from the house is a water-concentration problem. Capture the roof water, carry it away, then restore the soil.
This page is educational and does not replace an onsite evaluation. Conditions, codes and HOA rules vary by property.