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I am in the process of replacing 4 floor joists and the new 2x10s are 1/4" taller than what was previously there. I understand that as the lumber dries out it will shrink but how do i handle the 1/4" difference to have a level subfloor and not crack the tile i put on top.

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  • How are your old joists hung? If you can hang the new ones using metal hangers then they might be hung a bit lower and so match the old joists. A photo of the arrangement would help.
    – meld51
    Jan 30, 2020 at 7:20
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    Jan 30, 2020 at 13:09
  • The joists are sitting on the sill plate and center beam
    – Alex
    Jan 30, 2020 at 13:50

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I doubt your lumber will shrink 1/4" in width; it might shrink that much in length, but that won't affect your floor. Lumber has been cut differently over time. Just cut out a notch where the joist sits on the sill plate and center beam. If your lumber was too small, you would shim it, notching is just the opposite.

Once your subfloor is screwed or nailed with ring-shank nails(and glued to prevent squeaking) to the joist, there is little chance that there will be shrinking in a direction that causes any problems. Make sure you use quality flexible mastic under the tile and you will be fine.

I renovated an old house that had a variety of different thickness and width boards. You just notch and shim as much as you need to.

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    Be exceptionally careful with recommending notching a support beam of any sort. You'll probably get away with only 1/4", but any notching of a beam effectively makes the whole beam smaller. Where the beam sits on a support might (I'm not a structural engineer, so I don't know for sure) be OK, but people tend to hear "notch it" and forget that it applies only to certain areas, so they think they can notch any beam anywhere.
    – FreeMan
    Jan 30, 2020 at 18:43
  • Lumber doesn't shrink along the grain (in length), only across the grain (width and thickness).
    – tilde
    Jan 30, 2020 at 19:02
  • @tilde I'm sorry, but that's quite wrong. The simplest way to understand this is if you look at a hardwood floor. The wood flooring is installed with space between the flooring and the wall (lengthwise), in case of expansion. You will also note that gaps occur between the boards, lengthwise. I'm not saying it won't shrink in the other directions as well, but there is a lot less distance to shrink in thickness and width.
    – michael
    Jan 30, 2020 at 19:23
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    @FreeMan - Notching the end of a beam by 1/4 inch or so causes almost no loss of strength in the beam. The beam needs the most strength near the middle of the span.
    – Hot Licks
    Jan 30, 2020 at 19:33
  • @FreeMan As Hot Licks notes, there's no issue with this specific recommendation. But I agree it's important to understand what is OK and what' not: qis-tx.com/newsletter.0605.asp
    – JimmyJames
    Jan 30, 2020 at 19:47
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In my experiences there in no way to control how much a given piece of wood shrinks, that is if it has enough moisture content (MC) to shrink. If you could get it tested with a moisture meter for MC and it is around 6-8% preferably less, you can cut the joist to size for it will not shrink anymore. If the MC is 10% or more it will shrink and it will take a few weeks to get it to loose enough MC to not crack your tile. If you have kind of time to install the joists and wait for them to shrink in place in a heated environment, all the better. If you don't have that kind of time, then you will be better off purchasing LVL or other engineered lumber that does not move that much at all, unless it is really saturated.

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Unfortunately when dealing with replacing old lumber (or really any lumber with mismatched dimensions) you may have to buy kiln-dried new lumber and rip it to match the old dimensions.

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    A lot of times the problem is the opposit of what OP described. For example, old 2x4's really were 2" x 4" as opposed to the 1-1/2" x 3-1/2".
    – SteveSh
    Jan 30, 2020 at 12:53
  • Yes, and I'd leave the new ones 1/16" larger than the existing to allow for some shrinkage without causing flatness problems.
    – isherwood
    Jan 30, 2020 at 18:47

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