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  1. #1
    Join Date
    Dec 2011
    Posts
    24

    Default Deck framing question

    I will be rebuilding our deck in a few months and have a challenge. Currently, the deck is 10' deep from the house to the rail. It's constructed with joists hanging from a ledger board on the house, to a double 2x12 resting across steel columns set into the ground. The columns are about 5' tall. Pretty standard construction for a deck (I think). I want to rebuild the deck with an extra three feet of depth (13' from house to rail). I want to avoid pulling out the old columns and setting new columns, there are six of them, it's soft ground so they go deep, it's a lot of work. I don't want to cut them shorter and fix a new plate on them- it's require welding and who knows what to cut. Obviously I can't just lay joists across the top and cantlever them because the deck will be too high. So- here's my crazy idea: I want to run a double joist (probably 2x12) from the house out over each column- cantelevered to 13'. Then I'd attach a double 2x12 to the outside end and secure it with nails and upside down double joist hangers. With that framed- I'd just fill the rest in, hanging joists as you normally would from the house out to the double 2x12 on the end.

    I wasn't able to attach a drawing, hopefully this description is clear. Maybe the idea I have makes sense. But what I really wonder is, is this a totally stupid idea? It seems like this would carry load just as well as traditional construction... I'd like to think of this as a creative solution.

  2. #2
    Join Date
    Mar 2008
    Location
    nova scotia, canada
    Posts
    1,522

    Default Re: Deck framing question

    you will have to consult your local building authority and more than likely an engineer to see if your plan will work

    regarding cantilever.. the codes in most areas wont allow a cantilever of more than the equivalent of the width of the joist material.. meaning if you use 2x12 your cantilever can be no more than 11 - 1/4"
    fire up the saw and make some dust

  3. #3
    Join Date
    Jan 2009
    Location
    Needham, MA
    Posts
    559

    Default Re: Deck framing question

    codes do vary state by state but i believe you can do what you want to do. if i'm not mistaken you can cantilever a 2x12 floor joist up to 3' if the part that attaches to the existing joist overlaps the existing joist by 4'. basically what you have to do is to shorten the laly columns by 11 1/4 inches so that you can fit a double 2x12 on top of the columns and they will support the bottom of your existing joists. then you can cantilever out over the double 2x12 being sure to use carrriage bolts to secure the joists together. without me getting into all the fine details that's it in a nutshell. you can youtube a video on "how to cantilever deck joists".

  4. #4
    Join Date
    Jul 2010
    Location
    SoCal
    Posts
    6,472

    Default Re: Deck framing question

    Draw a plan and go to your building dept. They will tell you if you can do it or not.

    They can also tell you the length of cantilever you can do in your city.

    As a rule of thumb, I thought you could go about a quarter of the length of the joists, for joists 2x8 and higher. That's 2'6" for a 10' span. But as you can see, these numbers differ by location.

  5. #5
    Join Date
    Sep 2009
    Location
    florida
    Posts
    598

    Default Re: Deck framing question

    Quote Originally Posted by jkirk View Post
    you will have to consult your local building authority and more than likely an engineer to see if your plan will work

    regarding cantilever.. the codes in most areas wont allow a cantilever of more than the equivalent of the width of the joist material.. meaning if you use 2x12 your cantilever can be no more than 11 - 1/4"
    The distance your joists can safely cantilever or overhang a drop beam is determined by 3 factors.

    1) The size of the joists
    2) The type of material the joists are made from.
    3) The spacing between joists.

    Many building departments limit joist cantilevers to 2' or 3' maximums. At the end of the day the Licensed Engineer's calculations are the deciding factors.

    What size/height are your joist? 2x12?
    Gizmo

    Cut it 3 times & it's still to short.
    Inventor of the Miter Master Plus.

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  6. #6
    Join Date
    Dec 2011
    Posts
    24

    Default Re: Deck framing question

    Thanks everyone. I will have to check local codes on the cantilever. My support joists will be 2x12...

    I was hoping to avoid cutting the lally columns and supporting the joists off an end beam that was suuported on doubles that cross over the columns at their current height.

    ...I guess I would hire a welder to come in, cut the columns and affix a new plate on top. That's a little beyond my DIY skills.

  7. #7
    Join Date
    Jan 2010
    Location
    Northern Virginia
    Posts
    1,165

    Default Re: Deck framing question

    Is it a hollow steel lally column or structural steel (box or I)?
    If it's structural steel, simply attach a 2x12 on either side of it by drilling 1/2" holes through the steel and through-bolting with nut/bolt/washers. The steel will be trapped between two halves of the beam. You can add ripped blocks of wood at regular intervals between the columns so that the 2x12's can be attached to each other with more bolts.
    If you wanted to do a super job, have 4 pieces of 3x3x14 angle iron cut and bolt them beneath each 212 as solid bearing to the steel.

    If you have hollow steel columns with thin walls, you can proceed the same way, but to guard against crushing the circular-section post, you will need to fill them with cement before giving the bolts the final tightening. You could also box the lallys in with 2x4 and 2x8 to give solid bearing to the 2x12's. But they would need to bear of the footer unless you through-bolt.
    Casey
    Remove not the ancient landmark, which your fathers have set.

  8. #8
    Join Date
    Dec 2011
    Posts
    24

    Default Re: Deck framing question

    Thanks all! I like the bolt through idea- I hadn't thought of that. They are round steel columns- 4" diameter. I don't know if they're already filled with concrete, I'll need to check that out. They're pretty beefy though, it looks like the prior owner used the same kind of lally columns you use to support a center beam of a house in the basement.

    I appreciate all the help! Thanks!
    Dave

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