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  1. #1
    Join Date
    Sep 2007
    Location
    East Aurora, NY
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    3

    Post 2"x8" joists 20' span

    I recently purchased a home and began interior finishes demo. After removing the plaster and lath I found that the second floor joists are true 2x8s with 1x6 T&G sub-floor above making up the second floor. The house is 20 wide and currently has a partition wall running down the center breaking the 2x8 joists' span in half. The partition wall has no base plate and in some areas has no studs for up to 8 leaving simply the 2x4 top plate to support the joists above. I would like to eliminate the partition wall and open the full 20 span however I dont have enough head room to create a beam. Do you think I can get away with sistering 2x8 LVL beams onto every other joist (joists are 16 OC). The second floor will be bedrooms. The house is balloon framed therefore the sistered joists will be resting on a let in ledger at each end. Thanks for the advice.

  2. #2
    Join Date
    Aug 2007
    Location
    The Great White North
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    4,045

    Default Re: 2"x8" joists 20' span

    This sounds like you will need to have a professional evaluate the situation. There are too many variables to consider over the internet. For example the center bearing wall ( though from your description of being questionable ) helps with displacing the point load from the perimeter ledger ( or ribbon board ). If the floor joists are beefed up to handle the span there is the consideration of the ledger boards' integrity and ability to adequately handle the point loads.

    A professional would be able to offer solutions such as a flush mount beam midspan of the joists. This would replace the center support wall currently in place. This would be accomplished by installing temporary walls on either side of the center of the joists. Then cutting the joists in the center and inserting a properly engineered beam flush with the tops of those joists. The joists would then fastened to the beam with joist hangers. The depth of this beam would depend on how long the span is and what the calculated loads would be. For example if the depth of this beam is 10 inches ( hypothetically ) and your joists are 8 inches then there would only be 2 inches that would encroach into the ceiling space on the lower floor.

    There may also be other methods like the sistered LVLs you mentioned or sistering engineered floor trusses.

    Either way you will definitely need some professional input.

    Good luck.

  3. #3
    Join Date
    Sep 2007
    Location
    East Aurora, NY
    Posts
    3

    Thumbs up Re: 2"x8" joists 20' span

    I decided that it was a good idea to consult a professional. The following is an abbreviated version of the response I received.

    my approach: the max. span for a 2x8 2nd floor joist is 14' (of course thats for a Doug Fir #2 kiln dried..) so it is inadequate & technically can only support 70% of the 2nd floor load therefore we need to add additional members to support the remaining 30%+/- (or 10 psf of the total 30 psf live load). To do this I designed each LVL as a simple beam. And the short answer after running through options is this:

    Yes, your proposed solution will work BUT the new LVL's would have to be spaced @ 16" O.C. (tributary load spans of .67') AND they have to be high quality (see the Fb- 2.0E this is the determining factor some LVL's are only 1.8E) other factors are the LVLs need to be continuously braced by nailing thru the floor deck and this assumes there are NOT any 2nd floor load bearing walls (VIF), 1" bearing length should be fine although I would suggest running past the ledger & fastening to studs, plus these will only be 7-1/4" LVLs

    This goes to show its always better to consult a professional.

  4. #4
    Join Date
    Aug 2007
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    The Great White North
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    Default Re: 2"x8" joists 20' span

    This goes to show its always better to consult a professional.
    Yep ... especially in cases like yours.
    Sounds like the recommendation is to have the specified LVL sistered to each joist.

    Good luck.

  5. #5
    Join Date
    Sep 2007
    Location
    Long Island, NY
    Posts
    269

    Default Re: 2"x8" joists 20' span

    and when you go to do your new subfloor you might want to use T&G 3/4" Advantech glued and screwed to your joists for a real solid squeek free floor...
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  6. #6
    Join Date
    Jun 2007
    Location
    New Hampshire
    Posts
    13

    Default Re: 2"x8" joists 20' span

    Good idea on talking to a professional. There may be a cheaper solution however and this is something that you'd have to run by an engineer as well. But you might be able to install one large beam "flush" mounted where that old partition was located. You'd have to temporarily support the existing joists and cut them out at center span, install the beam and then use hangers at each joist. again, this solution might be cheaper but it MUST be designed by an engineer.

    Good luck,
    Todd Fratzel

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