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Depth of 1940s Granite block foundation wall

johns3km | Posted in General Questions on

I have a 1940s home outside of Boston that has granite block basement foundation with concrete slab, current unfinished ceiling height is 80”. I’m thinking of digging down, and I’m curious if anyone knows typically how far below the slab the foundation wall might be?

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  1. Expert Member


    It's a complete guess, but probably not far below the slab. I can't think of any circumstances that would have lead to digging a deeper excavation, but then back-filling much under the slab.

    1. johns3km | | #2

      Thanks, that’s what I figured.

  2. Expert Member
    NICK KEENAN | | #3

    It's a complete guess until you dig a test pit. And even then I've encountered foundations that weren't the same depth all the way around.

    But so long as we're guessing: if the house was finished in 1940 the foundation was probably dug in 1938 or so. At that time it was unlikely they used a machine, they probably dug by hand. Hand digging it's hard to imagine anyone overdigging and then filling, the stones are probably even with the bottom of the slab. I'd guess they went down 36" or so to get the bottom below the frost line and piled the spoils up around the outside to get the rest of the depth. Does the house look like it's on a little hill? It's really common for houses of that era.

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