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I want to level my first floor dining room.

The joists supporting the floor is 2x8", 13' long on that side of the main support beam.

They are spaced between 16 to 19" apart, there was some moisture that softened some of the joists.

I want to put a beam on each side of the main support beam, about 6 feet out, so it'll be in the middle of the 13' joists.

I do not know what size I should use to triple up the wood with 1/2" thick plywood between, 2x6, 2x8 or 2x10?

Also, what should I use as support columns for the beams?

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  • What's your specific question?
    – The Evil Greebo
    May 14, 2013 at 13:20
  • Do I triple up 2x6 or 2x8 to help level the floor?
    – Brad
    May 14, 2013 at 13:32
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    It's not clear what you're trying to do. Rephrasing the question, and/or adding pictures might help folks understand what you're asking.
    – Tester101
    May 14, 2013 at 14:29
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    Beams are usually used to correct overspanned joists. A beam is not a finesse tweak to a floor system. What are you ultimately trying to to with the room?
    – HerrBag
    May 14, 2013 at 14:46
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    Note that if you are installing a beam, you'll likely need a footer under the beam posts--unless you can span the beam to be carried by the foundation walls (which will take some retrofitting of the walls).
    – DA01
    May 14, 2013 at 15:24

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Beam jacking is as much art as science. It is a close cousin to house moving. The rate of increase must be gradual to prevent floor covering damage, wall damage and water and gas pipe damage.

The absolute amount you wish to lift will determine what is safe.

It may be that sistering new joists alongside the "water softened" ones is what you really need. A temporary jacking beam can be used to place the new joists and removed after they are lagged in place. Hopefully you can span from beam to side wall.

Beam construction design is based on material used (steel, glulam, fir), span distance (beam support to beam support) and load (the weight transferred from the joists above. As commented by DA01, a permanent beam will likely need footer support under your slab, because 2 beam supports represent 2 point loads that a 3" slab is not rated to support.

You would do well to research beam design and estimate loading, make a sketch and talk to an inspector about your design. Most inspectors I know will honor your research and give you general advice. Specific advice will come once you submit a permit request.

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