Backfilling a foundation
The soil against your foundation wall decides where rain goes. Done badly, it settles and sends water straight at the house.
Backfill is the soil placed back against a foundation wall after the hole is dug. And it needs to be compacted in layers and sloped away from the house. When it is loose or poorly shaped, it settles. The dip that forms collects water right at the wall.
This page prints no prices. It explains what good backfill does, so you can tell when yours has failed.
Why backfill matters more than it looks
Every foundation starts as a hole bigger than the house. Once the walls are up, the gap around them is filled in. That fill is the first thing rain meets after it leaves your roof.
Soil dug out of a hole is fluffy. It holds air that slowly squeezes out over a few years. The ground sinks as it does, and the sinking is worst right beside the wall, where the hole was deepest.
What good backfill looks like
Good work is boring to look at. The soil goes in as layers, and each layer is packed down before the next one goes on. The finished surface falls away from the house.
- Layers are compacted as they go, not dumped in one pass.
- Large rocks, lumber and construction debris stay out of the fill.
- The top layer is a denser soil that sheds water rather than soaking it up.
- The finished grade slopes away from the wall.
Pay attention to that last point. A slope that looks right on day one can disappear in a year.
Signs your backfill has settled
Look along the foundation after a heavy rain. A shallow trench of standing water against the wall is the clearest sign. Cracks in a patio or walkway that tilt toward the house tell the same story.
Soil that has dropped below the top of the foundation, or a gap between the soil and the wall, means the same thing. The soil pulling away from the foundation page explains why the gap opens and what it lets in.
Fixing a dip is usually small work
Adding soil to rebuild the slope is a reasonable first step. Use a dense, clay-bearing fill and pack it in thin layers. Do not use mulch or loose topsoil against the wall, because both hold water.
Keep the soil below your siding and below any wood framing. Soil piled against those invites rot and insects. Then make sure gutters are not dumping into the same spot. The grading and downspouts page covers the pair of changes that matter most.
When the dip keeps coming back
Soil that sinks again and again may be settling into a void or washing away underground. Check where the downspouts empty first. A buried line that has cracked, like the one described in buried downspout drain, can wash soil out from beside the wall.
If the wall itself is cracked or leaning, stop. That is not a landscaping question, and it belongs to a licensed structural engineer. An independent one has no repair to sell you.
Where to stop and call someone
Do not dig deep beside a wall you suspect is damaged. Removing the soil can take away support the wall was relying on. Rules about excavation and drainage are set locally, so ask your building department what applies before any large job.
Frequently asked questions
What is backfill around a foundation?
It is the soil placed back against the foundation walls after construction. It should be compacted in layers and sloped away from the house.
Why does soil sink next to my foundation?
Soil dug out of a hole holds air. It compacts over a few years, and the sinking is greatest beside the wall where the excavation was deepest.
What soil should go against a foundation?
A dense, compacted fill that sheds water, topped with a slope that falls away from the house. Avoid mulch and loose topsoil against the wall.
Can I fix a settled backfill myself?
Adding and compacting soil to rebuild the slope is a reasonable first step. Deep digging next to a cracked or leaning wall is not.
How far should backfill slope away from the house?
Rules and recommendations vary, so ask your local building department. The key point is that the ground should fall away from the wall, not toward it.
Sources
What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.
- US EPA. What You Can Do to Soak Up the Rain
- US EPA. Soak Up the Rain. Managing stormwater around a property