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Footing in garage conversion

Discussion in 'Residential Foundation Codes' started by zigmark, Apr 16, 2012.

  1. zigmark

    zigmark Silver Member

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    In the typical scenario of an owner wanting to convert an existing garage to livning space I was asked the following question;

    Could posts supporting beams at the floor joist midspan bear directly upon the existing garage slab if it were 6" thick?

    If yes, is this a perscriptive allowance?

    If not, why? and would you allow a pier footing, precast or otherwise, to be placed on top of the existing slab?

    Just curious how the rest of you deal with this stuff.

    ZIG
     
  2. Francis Vineyard

    Francis Vineyard Registered User

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    ZIG too many unknowns; what size column; tributary load and soil bearing Table R403.1 Precast see R402.3 Then there's moisture barrier for the slab and insulation, etc.

    Francis
     
  3. ICE

    ICE Moderator

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    It shouldn't be a problem to support a floor girder on a 6" garage slab. If you are concerned, add more posts. I have a truck that has weighed 8000# loaded and a 4" slab handles the point loads.

    You ask about a pier footing. A footing would work if what you mean is to cut the slab and dig out a footing. I don't think that that's what you meant. A pre-cast pier would not work just sitting on the slab because whatever you do must be secured to Earth.
     
    #3 ICE, Apr 16, 2012
    Last edited by a moderator: Apr 17, 2012
  4. Mark K

    Mark K Platinum Member

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    While this might carry some significant load I do not believe that this is consistent with the building code provisions. The cost of installing a new spread footing should be minor given the overall project costs.
     
  5. brudgers

    brudgers Platinum Member

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    A garage with a 6" slab isn't typical. Regardless, it doesn't meet code.

    It would not be surprising if there was no vapor barrier under the garage slab.

    And no footing under the area where the door will be infilled.
     
  6. ICE

    ICE Moderator

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    Yes but would it work?
     
  7. KZQuixote

    KZQuixote Sawhorse

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    OH My GAWD! Ice and I agree on something!

    I'd use a pony wall instead of a beam to avoid any point loads and even a 4" slab would support a residential floor system.

    Foggy
     
  8. Architect1281

    Architect1281 Gold Member

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    A 6 inch thick slab with a 2x 6 cripple wall will provide equivalent of 18" wide strip footing and at per thousand pound of assumed soil capacity would provide 1500 pounds of capacity per linear foot?

    IF the under floor area is considered conditioned space not subject to frost then most likely acceptable. point loads would need to be addressed by DRP provided calculations.
     
  9. zigmark

    zigmark Silver Member

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    Francis- I'm talking about general code requirements not about a specific job. With or without all of the information you requested, what about the code requirements?

    Brudgers- 6" slabs may not be common where you are and in our seismic zone there is always a footing under the door opening Addittionally if the slab is 4" or thicker no vapor barrier is necessary per this states energy code. So why exactly don't you feel it meets code? I do appreciate the input.

    ICE/KZQ- I'd agree that it seems to work and I'm not addressing a current project I am just curious about other jurisdictions out there and how they are dealing with the scenario.

    How about the provision of R403.1.1 that states "Footing projections, P, shall be at least 2 inches (51 mm) and shall not exceed the thickness of the footing."

    Thanks for all the input.

    ZIG
     

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