I'm looking to regrade the soil around my shed so water doesn't continue to damage the sill plate. The concrete slab is barely above grade, so I'm looking to remove soil to expose it another 2-3 inches. I'm concerned about potentially undermining the concrete slab by removing soil around it - Is it safe to remove the soil and expose the slab another couple of inches? Will this cause any issues with the foundation seeing as it's been this way for 18 years?

On the opposite side of the shed which is the last picture, the slab is exposed a good amount and there's no water damage to the sill plate. The shed is on a sloped hill, hence why that side is higher above grade.

Any input would be greatly appreciated.

Close up of sill plate and concrete slab

Area to excavate and re-grade

Opposite side of shed

  • 1
    That's not undermining. That's un-butrersssing. Which isn't a concern unless the whole thing is a literal A frame. You can dig all the way down to the footing. "Is it safe to excavate soil next to concrete slab?" Yes. and leave it that way? uh.... not if rain will then actually begin undermining it.
    – Mazura
    Commented Feb 15 at 5:39

1 Answer 1


The only issue would be if the regrade created a soil erosion problem that eventually removed soil from below the slab. As long as the compacted soil stays below the slab, you're fine. Assuming that the image's slab is level to the horizon and assuming that the soil conditions shown apply downstream (especially at any corners), your grade shouldn't be steep enough for an erosion problem. Something like grass with many shallow roots to stabilize things would be nice insurance.

For bridge piers in rivers, erosion vulnerable river bends, etc., "riprap" (a pile of boulders) is used to prevent soil erosion. It's a fun word to say. I seize any opportunity to utter it. If soil erosion seems to be developing after your regrade and you want bare soil for your landscape, then the solution is some kind of riprap. Don't freak out over any tiny sign of soil erosion, though. If your soil is a little silty, then some silt may wash out and leave behind a coarser soil that will suppress further soil erosion.

  • Start off by digging a small hole to determine the thickness of the slab. Commented Feb 15 at 8:26
  • This is roughly what I was going to say - dig out a trench, then retro-fill with gravel.
    – MikeB
    Commented Feb 15 at 10:38
  • @MikeB I would not backfill with gravel, unless you line with geotextile first.
    – Huesmann
    Commented Feb 15 at 11:44
  • @popham I would think an erosion control matting would be a better solution here than riprap. But since the OP doesn't give us a lot to work with in terms of pics, who knows? Certainly, my first step would be to put some actual topsoil and turf there, but it's not clear why water is a problem.
    – Huesmann
    Commented Feb 15 at 11:47
  • @Huesmann, my intuition for matting is that it's for very steep slopes, where you stake the stuff down and then plants can establish with roots tangled with the matting. Maybe you have something else in mind, though. I could see a weed-barrier type geotextile with decorative rock? (By riprap, I meant some kind of gravel that performs the same function as riprap, not literal boulders.) (I remember photos of this same office-on-top-of-a-slab from an earlier question.)
    – popham
    Commented Feb 15 at 19:44

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