Bouncy floor - repair from top?

jennifwAugust 23, 2010

I have a 1930's cottage with a 2nd story addition that was done in 1990. The 2nd floor has always been bouncy. We had some water damage and found what I think is the problem.

The floor joists are 2x6 on 16" centers. The span is about 13 feet in one place and more than 15' on the other side of the room.

I can't afford to pop the roof right now, but I am wondering if we can sister the joists from the 2nd floor down instead of the bottom up? (most of the notes on this board seem to be about repairing/reinforcing from the basement or under the house). The floor decking is particle board that is going to be ripped up anway (due to the water damage). If we do sister the joists, do you think another 2x6 or should we sister with a 2x8?

My simple water leak got expensive all of a sudden!

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If you use 2x8's you have to consider the height difference and if it will affect anything upstairs,( such as door openings ) as well as the top riser of the stairwell. You might want to consider decking it off with tongue & groove sturdi-floor 3/4" plywood.

    Bookmark   August 23, 2010 at 7:19PM
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If you can find manufactured I beam floor joists in the same size as the existing 2x6's, adding one of those every other space between the existing joists might be the best way to fix the bounce.

    Bookmark   August 24, 2010 at 12:05AM
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For the 15 ft span adding 1 3/4" x 5 1/2" LVL joists next to the existing 2x6 joists would meet the code required strength in bending but it would miss the required deflection limit. However, the maximum deflection at full design load would be reduced by half so the floor would feel much stiffer.

For the 13 ft. span you could probably get away with sistering with 2x6's or use the LVL's for a very stiff floor in that area.

If the added joists ends don't actually sit on the support walls, they must be very well nailed/bolted near the ends. Blocking to support joist hangers is usually a good idea. The added joists don't have to be touching the existing joists if the ends are well supported and braced. At these shallow depths blocking or bridging will not help much but it can't hurt.

    Bookmark   August 24, 2010 at 12:39PM
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Thank you for the replies. I hope this is just a temporary solution and we can do the full remodel next summer. I just don't want to put everything back together "broken."

    Bookmark   August 24, 2010 at 2:16PM
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