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Tops of Floor Joists Peaked

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  • Tops of Floor Joists Peaked

    I'm remodeling the bathroom in a 1950's home. After ripping out the old cracked and crumbling tile floor to replace with a new 3/4 ply sub floor, 5/16" cement board underlayment, and ceramic tile, I discovered that the tops of the floor joists had been chiseled or hacked to form a peak (see pictures).

    I'm not sure whether it would be ok to simply lay the new 3/4" ply sub floor on top of the floor joist with the tops peaked like that or whether something needs to be done to provide a broader surface.

    I've contemplated whether to sister 2x4 or 2x6s to each floor joist, or perhaps cut back the tops of each joist to just remove the peak then laminate a furring strip on the top, using an adhesive and fasteners, to restore the top plane of the floor joist without compromising the structural integrity of the joist.

    Your thoughts, comments, or suggestions would be greatly appreciated.

    Thanks,
    Tom
    Attached Files

  • #2
    Re: Tops of Floor Joists Peaked

    No idea why that was done. There may be a clue in your first pic. Do you know why the 2X material was added between the joists? This material seams to be newer than the surrounding wood structure and you can see that some of the hack marks translate onto the new material. Also looking closely the peaking was only done in the area that you ripped up, just beyond the boards that are torn up the joists appear to be flat. Since this is a bathroom perhaps it was done to remove rotted wood caused by a leaky fixture. I would likely rip them flat and add furring strips, it does not appear that there is room to sister in most areas.

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    • #3
      Re: Tops of Floor Joists Peaked

      That was a very common practice when installing ceramic tile back in the 30's to 60's. All ceramic was set on a concrete base (as you probably found out when you ripped it out) and the joist were tapered at the top to reduce the wood surface that would have a very thin layer of concrete over it. You haven't compromised the structual strenght of the jois, so I would recommend nailing a one by two or wider to the side of the joist to give an even surface to fasten your plywood floor.

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      • #4
        Re: Tops of Floor Joists Peaked

        was the tile set in a mortar bed directly on top of the wood just separated by some felt?

        If I remember correctly I have a 1950's book showing similar so the mortar bed would not crack as easily, by rounding the top of the joist, (or removing it)

        If the peak of the joist is there and the ply will set flat, I think one could just put the ply wood on top, of the peaked joist, and fasten it down, but it would not hurt to sister new up to it if there are doubts,
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        • #5
          Re: Tops of Floor Joists Peaked

          Originally posted by Pipestone Kid View Post
          That was a very common practice when installing ceramic tile back in the 30's to 60's. All ceramic was set on a concrete base (as you probably found out when you ripped it out) and the joist were tapered at the top to reduce the wood surface that would have a very thin layer of concrete over it. You haven't compromised the structual strenght of the jois, so I would recommend nailing a one by two or wider to the side of the joist to give an even surface to fasten your plywood floor.
          Learned something new again today, thanks

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          • #6
            Re: Tops of Floor Joists Peaked

            Thanks everyone for the replies. Looks like I'll sister up some new wood in spots, lightly plane a few high spots to get the floor level (currently about a 1/2" drop from one side of the room to the other with a slight rise in the middle). Then I'll be able to lay down a nice new level sub floor.

            Wayne, wasn't sure which picture you were referring to about the newer wood between the joists. In the first picture, that is all original material, except for the bit of new ply showing (sitting on top of the joist) in the upper right corner of the picture. In the second picture, The new material showing toward the bottom middle and also on the bottom right side of the picture is actually under the floor joists and part of a finished basement the previous owner did.

            BHD, the tile was set in mortar poured directly on the wood. No felt there whatsoever. Just some wire mesh around the perimeter of the room on the bottom of the mortar and tacked to the base plate of the walls.

            I've attached a few more of the several pictures I've taken during the demo. The first one shows the initial tear out of the floor and how boards were set between the joists which supported the mortar. The top of the boards were below the top of the joist by about 1" or so (the exception being where the tub was set to the left in the pics). Considering how thick this stuff was, I'm surprised they needed to recess it below the subfloor like that.

            The second picture shows all the tile and mortar removed, as well as the boards between the joists removed. You can also see the furring strips nailed to the side of the joist that supported the boards that were set between the joist.

            The last picture shows two large sections that I was able to lift out. You can see how the joist set in the mortar with the underside of the piece closest to the wall showing. Judging by the color and consistency of the mortar in these sections, it looks like the mortar might have been poured in a two step process.

            Thanks again for everyone's input and I hope you found the additional info and pics interesting and/or informative.

            Tom
            Attached Files

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            • #7
              Re: Tops of Floor Joists Peaked

              From what I was told is that this wasn't just done from the reducing the wood foot print, but it also created "Keys" that helped hold the concrete in place and kept it from settling. By tapering the joists, the concrete would be wider at the top than the bottom and would help hold it in place keeping the concrete from sliding down in the back and breaking the bond from the tile as the wood joists were now higher than the concrete.

              Hope that makes sense.

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