Thickness of wall sheathing

Discussion in 'Building Construction' started by Mark Smigel, Aug 17, 2005.

  1. Mark Smigel

    Mark Smigel Guest

    What thickness of =plywood= is typical for wall sheathing on
    residential construction? (for those builders who use plywood,
    not OSB)

    I have heard 1/2" is common, but I recently used this on a chicken
    coop and it seems to have marginal strength even for that application.
    I can't imagine it helping all that much with structural strength
    on a large house.

    MJ
     
    Mark Smigel, Aug 17, 2005
    #1
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  2. Mark Smigel

    Bob Morrison Guest

    In a previous post Mark Smigel wrote...
    > I have heard 1/2" is common, but I recently used this on a chicken
    > coop and it seems to have marginal strength even for that application.
    > I can't imagine it helping all that much with structural strength
    > on a large house.
    >


    1/2" (actually 15/32") is the most common. Its lateral strength depends
    on the size of nailing, nail spacing and the type of wood to which it is
    attached.

    From IBC2003, the typical design value for 1/2" nominal sheathing nailed
    to Douglas Fir framing with 8d commons at 6" o/c at the edges and 12"
    o/c in the field and all panel edges blocked = 260 lbs/ft for loads
    applied parallel to the wall. For example, a 4-foot wall panel will
    carry 1040 pounds of shear.

    If you decrease the nail spacing to 4" o/c at the edges, the design
    value jumps to 380 lbs/ft, or 1520 pounds for a 4-foot panel.

    So, as you can see 1/2" nominal plywood is pretty strong if nailed
    properly. BTW, 7/16" OSB has the same shear values when applied to
    studs that are 16" o/c.

    --
    Bob Morrison, PE, SE
    R L Morrison Engineering Co
    Structural & Civil Engineering
    Poulsbo WA
     
    Bob Morrison, Aug 17, 2005
    #2
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  3. Mark Smigel

    Bob Morrison Guest

    In a previous post P. Fritz wrote...
    > You imagine wrong......even gypsum board (if properly nailed) can be used
    > for shear walls
    >


    Paul:

    FYI

    Under IBC2003, the structural penalty for using GWB for shear walls in a
    seismic zone is severe. First, the R value used computing seismic
    forces must be decreased from 6.5 to 2.0. Since R is in the
    denominator, this has the effect of increasing the design force by a
    factor of 3.25. In addition, for seismic forces the capacity of a GWB
    shear wall must be reduced by half. This has the effect of increasing
    the design load to 6.5 times larger than if one uses plywood or OSB
    shear walls.

    So, for seismically controlled design, GWB shear walls are no longer
    practical.

    However, for wind controlled design GWB shear walls are still a viable
    and often practical alternative.

    --
    Bob Morrison, PE, SE
    R L Morrison Engineering Co
    Structural & Civil Engineering
    Poulsbo WA
     
    Bob Morrison, Aug 17, 2005
    #3
  4. Mark Smigel

    Bob Morrison Guest

    In a previous post P. Fritz wrote...
    > I've only used gyp. bd. shear walls occasionally and not in the last couple
    > of years....mostly in low rise (3 st) wood framed hotels and nursing
    > homes......there are always plenty on long solid interior walls
    > :)........that and I am in a lower siesmic zone than you.
    >


    Paul:

    I know. It seems a shame to not be able to use those nice long corridor
    walls that you have to cover with 5/8" GWB anyway for fire code reasons.

    I've taken to selectively sheathing the room side in those situations.
    Every other room or so has a slightly thicker wall because of the
    plywood on the room side. No one notices and it helps keep the cost
    down. The only real problem is that often that wall is also a plumbing
    wall, which I do not like to use for a shear wall because of all the
    holes that get punch in it.

    --
    Bob Morrison, PE, SE
    R L Morrison Engineering Co
    Structural & Civil Engineering
    Poulsbo WA
     
    Bob Morrison, Aug 18, 2005
    #4
  5. Mark Smigel

    RicodJour Guest

    Bob Morrison wrote:
    >
    > I've taken to selectively sheathing the room side in those situations.
    > Every other room or so has a slightly thicker wall because of the
    > plywood on the room side. No one notices and it helps keep the cost
    > down. The only real problem is that often that wall is also a plumbing
    > wall, which I do not like to use for a shear wall because of all the
    > holes that get punch in it.


    I think you've got that backwards, Bob. Ask any plumber, _you_ put
    that stupid structural crap in the way of _his_ plumbing! You should
    have known better.... ;)

    R
     
    RicodJour, Aug 18, 2005
    #5
  6. Mark Smigel

    Bob Morrison Guest

    In a previous post P. Fritz wrote...
    > Design is always a compromise. ;-)
    >
    >


    Indeed! A true statement that those of use who design stuff for a
    living must heed.

    --
    Bob Morrison, PE, SE
    R L Morrison Engineering Co
    Structural & Civil Engineering
    Poulsbo WA
     
    Bob Morrison, Aug 19, 2005
    #6
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