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  1. #1
    Join Date
    Apr 2009
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    3

    Default Leveling i-joists to install subfloor

    I am installing laminate flooring in the upstairs of my home. In one of the rooms, the subfloor was both unlevel and wavy. Also in some spots it would depress about 1/8" to 1/4" depending on where you stepped. I tried to screw it down tighter in those spots, but it didn't seem to help. Finally I pulled it up to find out what was going on. Under the floor are pre-fab OSB i-joists. None of are level with each other. I'm trying to figure out a way to get them level so that I can install a new subfloor. I was thinking about trying to sister 2x4s alongside them, but I don't know the best way to attach anything along the sides.


  2. #2

    Default Re: Leveling i-joists to install subfloor

    When we did addition we had these installed.

    They have markings on them with codes you can look them up and find out from the manufacturer what vintage they are and get the specification guides from the manufacturer.

    The stamped writing on them is directional so you can usually tell right away if they were installed upside down. The ways to stiffen and support them is different then regular lumber.

    Maybe its just an illusion but the edge on the top I think its called a flange looks wider than the bottom one. If they were installed upside down thats really bad. Our contractor did install some upside down and failed the middle inspection. When he removed the subfloor which was glued and screwed it hacked the edges up too much and they couldn't be removed and reinstalled according to the inspector they were too damaged since it was more expensive for the contractor to get a manufacturer rep or engineer to inspect on site to argue in his favor he was forced to replace the ones that the inspector didn't like and flip the remaining upside down ones and reinstall. We were lucky we didn't have to pay for his mistakes but from that point on we hired an independent home inspector and had him come by frequently to check on status of things he caught a LOT of mistakes and forced the contractor to do things right. The independent home inspector cost us all told $900 for his many visits and reports with full documention but saved us thousands and a botched addition. We were lucky we didn't get stuck with any of that nasty chinese drywall either our inspector was wise to the problem long before it was on the national news.

  3. #3
    Join Date
    Apr 2009
    Posts
    3

    Default Re: Leveling i-joists to install subfloor

    Quote Originally Posted by jkirk View Post
    how out of level are the i-joists, if its by an 1/8" thats do to manufacturing. the plys on the top and bottom chords arent always dead on the same they can vary from one to the next, if its only minor i wouldnt worry about it too much. however if they are out by 1/4 or more then deal with it. the easiest way is to make thin strips ripped out of 2x4 to make them even, glue these down with construction adhesive to the tops of the tji's and then more construction adhesive on top of that for the new sheathing


    My problem starts in the upper corner. That part of the wall is adjacent to a bathroom and there appear to be extra supports for the bathtub which extend into the floor area of the room where I'm working. Those supports are 1/2" to 3/4" higher than the lowest section of the floor and the drop off is too steep to ignore. If not for this section, the variations in the floor wouldn't be "that" bad.

  4. #4
    Join Date
    Apr 2009
    Posts
    3

    Default Re: Leveling i-joists to install subfloor

    Quote Originally Posted by jkirk View Post
    can you plane them down to be flush with the rest of the floor
    Good question. I don't know how much I can shave off the top of those things. I don't see any labeling on them to let them me know where to look up a spec sheet. If I could shave that corner down, it'd sure save me a lot of work.

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