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rotted joists on a cantilevered 3rd story deck

tow | Posted in General Discussion on April 1, 2011 11:08am

We have an 8 foot deep cantilevered deck on the upper (3rd ) floor on one side of the house.  The deck runs a total width of 28 feet (outside the living room and main bedroom).  The house is 64 yrs old, and some of the deck joists had rotted on the outer ends.  We sistered each of the joists along the full outer 8 feet.  (the rotted ends were cut off and the joists were reverse sistered, if that makes sense).  

The joists measure 1 1/2 x 11 1/2, and are now (sistered) approximately 12 inches apart.  We’re not sure how far into the room the joists run.  But their length in the room cannot be more than 8 feet, since a staircase leading downstairs begins 8 feet from the (deck) edge of the house. 

We’ve used the deck over the years and eat dinner and sit out on it regularly.  The only issue we’ve noticed is that when someone walks on the deck, the living room floor vibrates somewhat. 

Should we be concered about the extra weight now that we’ve sistered the joists?  If so, any recommendations as to how we can increase its soundness?

Many thanks in advance.

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Replies

  1. junkhound | Apr 02, 2011 07:16am | #1

    Full 8 foot cantilever!!

    Is there a beam out toward the end for support, or is it really a full cantilever as implied?

    2x12 12" OC -- OK, that would allow for about a 35psf loading, but a 'little' bouncy at the end, which translates into the LR - can believe the floor vibration!

    Extra weight of the sistered joists is trivial compared to other factors.

    E.G, -- How much was cut off the ends?? The moment connection is the critical part. Did you glue with waterproof glue? Bolted vs simply nailed with a few 3" NG nails?

  2. DanH | Apr 02, 2011 07:50am | #2

    Yeah, the extra weight is negligible, and has nothing to do with the bounce you experience.

    How much of each joist was cut off?  If not more than 2-3 feet worst case then there should be no problem with the sistering.

  3. warrenblack1 | Apr 02, 2011 09:14am | #3

    cantilievered joists

    If the ceiling below the living room is drywall then I would cut out the  the drywall 4 ft from outside wall and extend the sistering of the joists back into the 4 ft area inside. The addition of some full blocking between these ceiling  joists at the end of the deck joists can held also.

    1. tow | Apr 02, 2011 01:20pm | #4

      thanks!

      for the replies.

      Yes, this is essentially a full 8 ft cantilever, with no vertical beam support for the 28 ft width. Tthe right-most 8 foot stretch of the cantilever consists of  3 ft deep exposed decking (sort of becomes an outside walkway) with the remaining 5 ft depth consisting of the enclosed (walled) outer left-most part of the main bedroom (hope this makes sense).  I say "essentially" an 8 ft cantilever because at the right-most edge of the cantilever, the two lower stories of the house jut out 3 feet farther than the left-most part of the lower stories.  So there is a 3ft deep vertical wall that provides some vertical support at the right-most 3ft inner edge of the cantilever, beneath the bedroom.

      No more than 3 ft of the joists were cut off, and the sistering was done using bolts. 

      We'd like to inspect and possibly strengthen the living room joists.  We have to bit the bullet and replace the living room flooring and were thinking of inspecting the joists from the top, rather than from the downstairs bedroom.  Hoping this would work?

      1. sapwood | Apr 02, 2011 10:02pm | #5

        Personally, I cannot visualize your situation at all. Your description is somewhat lacking. You mention vertical beams where you probably mean column so I'm left to wonder what other terms you are mixing up. Additionally, you probably have an overhanging deck and not a cantilever. The terms are often used interchangeably but shouldn't be. Some photos would be helpful.

        1. DanH | Apr 02, 2011 10:31pm | #7

          Additionally, you probably have an overhanging deck and not a cantilever.

          How does an overhanging deck without vertical supports differ from a cantilever?

          1. sapwood | Apr 03, 2011 10:37pm | #8

            I've always understood a cantilever to be affixed by a moment connection. A cantilevered member originates at the point of connection. An overhanging member can originate and be affixed in a number of places... it extends away from that point and is supported at an additional point from which it extends into unsupported space.

      2. Piffin | Apr 02, 2011 10:14pm | #6

        can you hear me whistle?
        I wouldn't touch that without consulting an engineer first.

  4. warrenblack1 | Apr 09, 2011 07:55pm | #9

    Inspecting of modifying from above (thorough the floor as you desire) is not a problem. I suggested the ceili9ng because drywall is cheaper than flooring, but not if you already intend to remove flooring.

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