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Footing width table Q.

Discussion in 'Residential Building Codes' started by Pcinspector1, Nov 7, 2018.

  1. Pcinspector1

    Pcinspector1 Platinum Member

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    Q. The IRC 2012 Table R403.1

    What would the footing width be for a 2-story on 2,000 lb soil using poured foundation walls? Light frame construction for the walls above the foundation.

    Is 12 inches correct?

    We typically see 16-inch wide footings here, I think its for the goof factor?
     
  2. Builder Bob

    Builder Bob Sawhorse

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  3. Pcinspector1

    Pcinspector1 Platinum Member

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    Has a 20 snow load.

    Does the table indicate 12-inches minimum? It would be conventional light frame construction.

    Not sure if I understand what 8-inch solid masonry means on the table which leads me to believe it should be 21-inches?
     
  4. Ty J.

    Ty J. Sawhorse

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    12x6 is the minimum required.

    Check with the AHJ, some jurisdictions require that 1500psf be assumed unless supporting geotech indicates a greater bearing value may be used, which would require 15x6 footings..


    As a cautionary note, the minimum footing widths established under Table R403.1 are only based upon 20-ft of roof tributary at 50-psf snow load, 16-ft of floor tributary, 10-ft first story walls, and 8-ft second story walls. If your design uses spans imparting greater tributary, footings may need to be increased.

    This is reflected in the 2015 IRC by footnote "b" of Table 403.1(1). Per the 2015 IRC, footings follow the table, then are increased at a prescribed rate of 2-in to width and 1-in to depth for every 2-ft of building width over an assumed width of 32-ft.

    As an example, a 40-ft wide home with a center load bearing wall of conventional 2-story construction would require 24x10 footings (16x6 typ. + 8-ft adjustment [8x4] = 24x10).

    Generally speaking, following footnote "b" of the 2015 IRC will greatly oversize footings because it is based upon a floor and roof system bearing on a center load bearing wall. Thus, this footing is sized for 50% of all roof and floor loads. Given the 40-ft example home, it is infeasible to assume that the floor system would clear span 20-ft to the center wall, whereas roof system is manageable with trusses.
     
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  5. Ty J.

    Ty J. Sawhorse

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    Masonry built home.

    Conventional light frame includes a typical concrete foundation.
     
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  6. JBI

    JBI Sawhorse

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    Don't forget the footnotes... tables are based on a 32' wide home with center bearing wall, adjustments for wider or narrower home in footnote b.
    The 2015 IRC for 2 story light frame above a basement is 16" minimum for 20# snow load and 2,000# soils.
    Remember these are 'prescriptive' provisions, not the be all and end all. They can always go above code minimum.
     
  7. HForester

    HForester Member

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    2 foot excavator bucket...get it done with some safety factor
     
  8. Pcinspector1

    Pcinspector1 Platinum Member

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    Any inspectors using a pocket penetrometer probe to check soil pressure?
     
  9. Pcinspector1

    Pcinspector1 Platinum Member

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    [​IMG] pocket Penetrometer
     
  10. Keystone

    Keystone Sawhorse

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    To anyone using a penetrometer, STOP. These devices are not to be used in determining soil bearing in a structural application. These devices are an industry joke that is another greatly marketed play item. I suggest anyone contact the manufacture of the device and they will tell you the penetrometer is not to be used in a structural application...

    At plan review we assume soil bearing to be 1500PSF.
     
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  11. Pcinspector1

    Pcinspector1 Platinum Member

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    I don't have a penetrometer or have I seen a turd party inspector use one but couldn't believe they are very accurate. With that said, I still do a footing inspection and was taught to use my heal of my boot, maybe this is for show?

    Which would you trust more?
     
  12. HForester

    HForester Member

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    Incredible.....
     
  13. Keystone

    Keystone Sawhorse

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    When I started in the direction of building inspector I spent some time with a engineering company, training and field work of soils, concrete and asphalt so I know enough to be dangerous but not smart. Ill visually look, use my foot and ball it in my hand.
     

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