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Thickened edge slab climate 4C

joenorm | Posted in General Questions on

I am wondering if anyone can shoot from the hip and recommend a footing width and depth for a shed building that will be built on a slab foundation with thickened edge.

The building will not be getting permits or any engineering. The slab will get 2 inches of foam underneath and foam on the sides and well. 

Climate is 4C near Seattle

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  1. jollygreenshortguy | | #1

    "Shed", if you're talking about something like a garden shed, under 120+- sq. ft. I wouldn't worry about it. I'd aim for a trench a shovel's width wide and deep. But if you're talking about something the size of a garage then I'd go with the requirements of IRC2021 R403.1 and aim for the bottom of the footing to be 1' below final grade and for the footing to be 1' wide.

    1. joenorm | | #2

      thanks. This will be more like a garage. And the kicker that I did not mention is I would like to plan to build 2-story onto it in the future. Assume good bearing soils. Building size is 16x24

  2. Expert Member
    Michael Maines | | #3

    No, but I can give you the code reference so you can figure it out: Regardless of permits or engineering, the IRC is a good baseline for minimum building standards.

    1. joenorm | | #4

      Thanks. I am surprised that footing widths when doing a slab on grade are allowed to be significantly narrower

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