Deck Joist Span Length?

Discussion in 'Building Construction' started by Bubba Bean, Sep 14, 2004.

  1. Bubba Bean

    Bubba Bean Guest

    i seem to recall from my old deck building days that you can
    canitlever a joist 33% of the length of the joist. I want to build a
    12 foot wide deck and have the beam at 8 feet with 4 feet of the joist
    extending past. Is my memory still accurate? Thanks in advance.
     
    Bubba Bean, Sep 14, 2004
    #1
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  2. It wouls work as long as the 8' part is fastened to the house.
    And I would put the crowns DOWN on the joists.

    --
    JerryD(upstateNY)

    "Bubba Bean" <email> wrote in message
    news:...
    i seem to recall from my old deck building days that you can
    canitlever a joist 33% of the length of the joist. I want to build a
    12 foot wide deck and have the beam at 8 feet with 4 feet of the joist
    extending past. Is my memory still accurate? Thanks in advance.
     
    JerryD\(upstateNY\), Sep 15, 2004
    #2
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  3. Bubba Bean

    BP Guest

    The distance any beam can cantilever (a joist is a beam) is determined by 1)
    the size of the beam, and 2) the loading on the beam. There is no "rule"
    about 1/3 the span. There are "conventions" such as a second floor
    cantilever on a garrison home being 18" for a 2x8 and 24" on a 2x10, but
    these are just "the way we've always done it" rules. And the loading is less
    on the second floor of a garrison cantilever. Best to get that cantilever
    calculated by an engineer. Many full service lumberyards have someone who
    can calc simple cantilevers for you.
    And the crowns do not go down and would have no effect on the strength of
    the cantilever. It would just make a poorly built deck look "right" longer.

    "Bubba Bean" <email> wrote in message
    news:...
    > i seem to recall from my old deck building days that you can
    > canitlever a joist 33% of the length of the joist. I want to build a
    > 12 foot wide deck and have the beam at 8 feet with 4 feet of the joist
    > extending past. Is my memory still accurate? Thanks in advance.
     
    BP, Sep 15, 2004
    #3
  4. Why would you want the crowns up ?
    The part of the deck cantilevered out would run downhill right from the
    start.
    And it will only get worse as time goes by.

    --
    JerryD(upstateNY)
    "BP" <> wrote in message
    news:...
    The distance any beam can cantilever (a joist is a beam) is determined by 1)
    the size of the beam, and 2) the loading on the beam. There is no "rule"
    about 1/3 the span. There are "conventions" such as a second floor
    cantilever on a garrison home being 18" for a 2x8 and 24" on a 2x10, but
    these are just "the way we've always done it" rules. And the loading is less
    on the second floor of a garrison cantilever. Best to get that cantilever
    calculated by an engineer. Many full service lumberyards have someone who
    can calc simple cantilevers for you.
    And the crowns do not go down and would have no effect on the strength of
    the cantilever. It would just make a poorly built deck look "right" longer.

    "Bubba Bean" <email> wrote in message
    news:...
    > i seem to recall from my old deck building days that you can
    > canitlever a joist 33% of the length of the joist. I want to build a
    > 12 foot wide deck and have the beam at 8 feet with 4 feet of the joist
    > extending past. Is my memory still accurate? Thanks in advance.
     
    JerryD\(upstateNY\), Sep 17, 2004
    #4
  5. Bubba Bean

    BP Guest

    This "rule" is as old as framing with wood. It applies to all joist framing,
    in or out. The crowns go up because the weight of the materials tends to
    press down on the beam and "deflect" it. In theory the natural crown would
    be pressed flat. This does not happen immediately in most cases but happens
    gradually over time. If you put the crowns down the depression in the middle
    would grow deeper over time. When you buy glue-lam beams you can have them
    engineered and built with a designed crown that will flatten to level once
    it is fully loaded. They do it with steel also. You see this much more in
    commercial structures where loads and spans are much greater (and the money
    for structural engineering is much more plentiful).

    "JerryD(upstateNY)" <> wrote in message
    news:ehp2d.232670$...
    > Why would you want the crowns up ?
    > The part of the deck cantilevered out would run downhill right from the
    > start.
    > And it will only get worse as time goes by.
    >
    > --
    > JerryD(upstateNY)
    > "BP" <> wrote in message
    > news:...
    > The distance any beam can cantilever (a joist is a beam) is determined by

    1)
    > the size of the beam, and 2) the loading on the beam. There is no "rule"
    > about 1/3 the span. There are "conventions" such as a second floor
    > cantilever on a garrison home being 18" for a 2x8 and 24" on a 2x10, but
    > these are just "the way we've always done it" rules. And the loading is

    less
    > on the second floor of a garrison cantilever. Best to get that cantilever
    > calculated by an engineer. Many full service lumberyards have someone who
    > can calc simple cantilevers for you.
    > And the crowns do not go down and would have no effect on the strength of
    > the cantilever. It would just make a poorly built deck look "right"

    longer.
    >
    > "Bubba Bean" <email> wrote in message
    > news:...
    > > i seem to recall from my old deck building days that you can
    > > canitlever a joist 33% of the length of the joist. I want to build a
    > > 12 foot wide deck and have the beam at 8 feet with 4 feet of the joist
    > > extending past. Is my memory still accurate? Thanks in advance.

    >
    >
     
    BP, Sep 17, 2004
    #5
  6. I have framed many many houses and realize that you put the crown up on
    floor joists and rafters.
    With any joist/rafter fastened at each end, when the it settles, it becomes
    straight.
    With the cantilever floor joist on the deck, I would still put the crown UP.
    The cantilevered part of the deck will never go up.
    Because it will have the weight of the railing on it, it will go down.
    When it goes down, it will be level with the rest of the deck.

    --
    JerryD(upstateNY)

    "BP" <> wrote in message
    news:...
    This "rule" is as old as framing with wood. It applies to all joist framing,
    in or out. The crowns go up because the weight of the materials tends to
    press down on the beam and "deflect" it. In theory the natural crown would
    be pressed flat. This does not happen immediately in most cases but happens
    gradually over time. If you put the crowns down the depression in the middle
    would grow deeper over time. When you buy glue-lam beams you can have them
    engineered and built with a designed crown that will flatten to level once
    it is fully loaded. They do it with steel also. You see this much more in
    commercial structures where loads and spans are much greater (and the money
    for structural engineering is much more plentiful).

    "JerryD(upstateNY)" <> wrote in message
    news:ehp2d.232670$...
    > Why would you want the crowns up ?
    > The part of the deck cantilevered out would run downhill right from the
    > start.
    > And it will only get worse as time goes by.
    >
    > --
    > JerryD(upstateNY)
    > "BP" <> wrote in message
    > news:...
    > The distance any beam can cantilever (a joist is a beam) is determined by

    1)
    > the size of the beam, and 2) the loading on the beam. There is no "rule"
    > about 1/3 the span. There are "conventions" such as a second floor
    > cantilever on a garrison home being 18" for a 2x8 and 24" on a 2x10, but
    > these are just "the way we've always done it" rules. And the loading is

    less
    > on the second floor of a garrison cantilever. Best to get that cantilever
    > calculated by an engineer. Many full service lumberyards have someone who
    > can calc simple cantilevers for you.
    > And the crowns do not go down and would have no effect on the strength of
    > the cantilever. It would just make a poorly built deck look "right"

    longer.
    >
    > "Bubba Bean" <email> wrote in message
    > news:...
    > > i seem to recall from my old deck building days that you can
    > > canitlever a joist 33% of the length of the joist. I want to build a
    > > 12 foot wide deck and have the beam at 8 feet with 4 feet of the joist
    > > extending past. Is my memory still accurate? Thanks in advance.

    >
    >
     
    JerryD\(upstateNY\), Sep 17, 2004
    #6
  7. Bubba Bean

    BP Guest

    I'll have to take your word on that.

    "JerryD(upstateNY)" <> wrote in message
    news:qUI2d.3141$...
    > I have framed many many houses and realize that you put the crown up on
    > floor joists and rafters.
    > With any joist/rafter fastened at each end, when the it settles, it

    becomes
    > straight.
    > With the cantilever floor joist on the deck, I would still put the crown

    UP.
    > The cantilevered part of the deck will never go up.
    > Because it will have the weight of the railing on it, it will go down.
    > When it goes down, it will be level with the rest of the deck.
    >
    > --
    > JerryD(upstateNY)
    >
    > "BP" <> wrote in message
    > news:...
    > This "rule" is as old as framing with wood. It applies to all joist

    framing,
    > in or out. The crowns go up because the weight of the materials tends to
    > press down on the beam and "deflect" it. In theory the natural crown would
    > be pressed flat. This does not happen immediately in most cases but

    happens
    > gradually over time. If you put the crowns down the depression in the

    middle
    > would grow deeper over time. When you buy glue-lam beams you can have them
    > engineered and built with a designed crown that will flatten to level once
    > it is fully loaded. They do it with steel also. You see this much more in
    > commercial structures where loads and spans are much greater (and the

    money
    > for structural engineering is much more plentiful).
    >
    > "JerryD(upstateNY)" <> wrote in message
    > news:ehp2d.232670$...
    > > Why would you want the crowns up ?
    > > The part of the deck cantilevered out would run downhill right from the
    > > start.
    > > And it will only get worse as time goes by.
    > >
    > > --
    > > JerryD(upstateNY)
    > > "BP" <> wrote in message
    > > news:...
    > > The distance any beam can cantilever (a joist is a beam) is determined

    by
    > 1)
    > > the size of the beam, and 2) the loading on the beam. There is no "rule"
    > > about 1/3 the span. There are "conventions" such as a second floor
    > > cantilever on a garrison home being 18" for a 2x8 and 24" on a 2x10, but
    > > these are just "the way we've always done it" rules. And the loading is

    > less
    > > on the second floor of a garrison cantilever. Best to get that

    cantilever
    > > calculated by an engineer. Many full service lumberyards have someone

    who
    > > can calc simple cantilevers for you.
    > > And the crowns do not go down and would have no effect on the strength

    of
    > > the cantilever. It would just make a poorly built deck look "right"

    > longer.
    > >
    > > "Bubba Bean" <email> wrote in message
    > > news:...
    > > > i seem to recall from my old deck building days that you can
    > > > canitlever a joist 33% of the length of the joist. I want to build a
    > > > 12 foot wide deck and have the beam at 8 feet with 4 feet of the joist
    > > > extending past. Is my memory still accurate? Thanks in advance.

    > >
    > >

    >
    >
     
    BP, Sep 18, 2004
    #7
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