My two-and-a-half story house has an ordinary inverted T strip foundation (no slab). I’m digging out some of the (heavy clay) soil in the crawlspace under the house to try to get some standing room under there, and simultaneously digging on the other side of the foundation walls for a French drain. So I’m wondering, does the soil I’m digging out, the soil either side of the foundation above the level of the bottom of the footing, play any role in supporting the house? I would imagine that when the clay under the footings gets wet it looses much of its bearing capacity and begins to act like mud, squishing out from under the weight of the footings. Does the soil I’m digging out counteract this by pressing down right beside the footing to keep that presumably squishy soil in place?
The code here in California (’97 Uniform Building Code, Table 18-1-C) requires that the bottom of my footings be 24″ below grade (“below undisturbed ground”), but then says (in footnote #2) that I can excavate the soil in the crawlspace to the depth of the top of the footing. That leaves 8″ of “overburden” above the level of the bottom of the footing on the crawlspace side and 24″ on the outside. I’m not seeing what sense this makes. The soil here never freezes, so frost heave is not an issue.
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Does the soil I’m digging out counteract this by pressing down right beside the footing to keep that presumably squishy soil in place?
Maybe a little bit. More importantly, the soil that remains beside the footer, and beside the foundation wall, keeps the footer and wall from moving sideways. If the foundation wall is concrete, this won't be an issue for the wall.
And if your local codes say not to dig beyond the top of the footer, then don't. Those codes exist for good reasons. Since I've never lived in your area, I have no idea what those reasons are -- but I'd bet they're good reasons.
Proud parent of a terriffic kid, who sells term papers to honor students.
Codes exist for good reason? Well, perhaps most of the time and this is likely one of those times. However, there are hundreds of codes which I believe exist to line the pockets of various manufacturer, and to save insurance companies money (but not necessarily result in a net savings for society). Then there is just plain old arrogance. Cities and counties want to be seen as independent and just change the code to be seen as not just buying off on generally accepted national codes.
Tons of politics here. Just a little side note.