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Activity Feed Forums Floor Prep Flattening very uneven subfloor Reply To: Flattening very uneven subfloor

  • Andy

    July 6, 2023 at 10:51 am

    It’s been months, but I’m still slowly at it. Then kids came home from college & didn’t want me ripping up their rooms, etc. Anyway, to continue with uneven subfloor issues:

    To recap: I have engineered truss floor joists, as seen in a photo above. These trusses are supposed to be strong, but they are not straight/flat. Putting a long level on the visible ones in the basement shows how they go up and down over their lengths; they are not only bowed down from weight sitting on them.

    Example: the latest room where I removed the carpet has a 1″ drop from one outside wall to the other inside wall, and a 1/2 inch drop the other direction. And it isn’t a flat drop; the floor curves in various ways.

    1) Q: Do I need a structural engineer to come inspect my house?

    There are gaps under wall base plates that are 1/8 to 1/4 inch in some places – I can slide thick cardboard under the wall from one room to another. Even some exterior walls have gaps under them. I think the house is structurally sound & this is just because of the truss variation. There are no cracks in walls where things have settled/changed over the years, so I’m guessing this is because the pre-built wall sections were put up & the “wall box” didn’t touch in some places along the length of the base plate.

    Part of this was found when a floor squeak remained after screwing all the subfloor down & removing popped nails. The squeak was under the wall base gap. Oh, and also squeaks in spots where tongue & groove subfloor was not used, so the edges moved against each other. Some plywood is marked on top: “other side up”. The builders of my house were lazy and slapped it together in 1983. Tract housing.

    2) I was originally going to try flattening the entire 2nd floor so I could have an unbroken floor, but there is so much variation, I think it would be better to flatten each room and the hallway separately. Each doorway might have a slight height transition, but I can’t see trying to flatten it all into 1 single plane. The hallway at the top of the stairs will already add 1-1.5 inches to the top step/landing as it is, so trying to flatten it to other rooms would mean it would be even higher.

    Q: Does all this separate flattening sound bad? The doorway transitions should be no more than 1/4 inch or so, so it isn’t like they would have huge steps like a couple places in the 1st floor.

    3) The biggest height variations will be into rooms that I’m not redoing, such as the hall bathroom. Since the hallway will now be higher, I believe I’ll have to remove the marble threshold and add some new threshold when done to do the height transition. I guess there is no real question on this one; just commenting in case you read it & have something to say about it.

    This house is a bit frustrating, in case that wasn’t obvious. I’ve had a few choice words in some of the empty rooms.