What is the minimum depth of slab on grade

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catour
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What is the minimum depth of slab on grade

Post by catour » Sat Sep 14, 2019 8:27 pm

My old shed is built on an 8" concrete slab and I wonder how much I can lower the grade around the shed before the slab is exposed too much? E.g. is it okay if the bottom of the slab is just 3" below ground and the top of the slab is 5" above ground?

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Shannon
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Re: What is the minimum depth of slab on grade

Post by Shannon » Sat Sep 14, 2019 8:33 pm

Sure that is fine. You just want to avoid being so low with the grade that the gravel fill under the pad can sluff out from under the edges.
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A. Spruce
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Re: What is the minimum depth of slab on grade

Post by A. Spruce » Sat Sep 14, 2019 9:19 pm

Yup, so long as the slab cannot be undermined by natural runoff, it can sit directly on top of grade.
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catour
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Re: What is the minimum depth of slab on grade

Post by catour » Sun Sep 15, 2019 9:24 am

Thanks so much. Although it's another topic, but still relevant to regrading: if grade around house foundation is lowered by 5" do you think the basement will become noticeably colder in winter?

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A. Spruce
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Re: What is the minimum depth of slab on grade

Post by A. Spruce » Sun Sep 15, 2019 9:41 am

I wouldn't think so, but I'm not a basement guy. Why would you lower the grade by 5", and are you absolutely certain that by doing so that you're not creating a negative grade that will cause water to pool at the house?
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Shannon
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Re: What is the minimum depth of slab on grade

Post by Shannon » Sun Sep 15, 2019 7:17 pm

Ya it should not effect temp in basement. But as Spruce mentioned be sure this is not creating a negative grade back towards house
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catour
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Re: What is the minimum depth of slab on grade

Post by catour » Mon Sep 16, 2019 7:35 am

Thanks for your answers. I'm re-grading my whole backyard, so the proper slope will be preserved.

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