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Thickened slabs for Interior load bearing walls?

Discussion in 'Residential Foundation Codes' started by rktect 1, Oct 18, 2011.

  1. rktect 1

    rktect 1 Gold Member

    Oct 20, 2009
    Likes Received:
    Is there anywhere specifically in the 2006 IRC that requires a thickened slab for an interior load bearing wall?

    Generally, I don't have to ask DP's to provide these. They just do. No rhyme or reason for sizes but generally noted somwhere on the set. So where is the requirement located? If anywhere? IRC or ACI 318?

    The IRC does provide a figure R403.1(1) in the upper right hand corner. But no other information. Or am I to assume that this figure goes along with section 403.1 which requires 12" in width minimum, then tie that section into 403.1 requiring a minimum depth of 6 inches?
  2. mn joe

    mn joe Silver Member

    Jan 5, 2010
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    The requirement is not necessarily for a thickened slab. Section R403 is titled footings, but figure 403.1(1) is titled concrete and masonry foundations. The 2 terms seemed to be interchangeable. Figure 403.1(1) shows W(width) as a variable dependent on the load imposed by the bearing wall above. If it was not a bearing wall it could be posts supporting a beam. Any load bearing point or wall will require an adequate foundation. The IRC is not specific on how to support these bearing points. You can always fall back on section R106 and say that the foundation design is part of the required construction documents.

  3. mtlogcabin

    mtlogcabin Registered User

    Oct 17, 2009
    Likes Received:
    Interior bearing walls will support different loads and the foundation for that wall needs to be designed accordingly. It may carry the same loads as the exterior walls or substantially less.

    R401.2 Requirements.

    Foundation construction shall be capable of accommodating all loads according to Section R301 and of transmitting the resulting loads to the supporting soil. Fill soils that support footings and foundations shall be designed, installed and tested in accordance with accepted engineering practice. Gravel fill used as footings for wood and precast concrete foundations shall comply with Section R403.

    R403.1.4.2 Seismic conditions.

    In Seismic Design Categories D0, D1 and D2, interior footings supporting bearing or bracing walls and cast monolithically with a slab on grade shall extend to a depth of not less than 12 inches (305 mm) below the top of the slab.
  4. gbhammer

    gbhammer Platinum Member

    Aug 1, 2011
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    mt has got it.

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