Levelling Joists

Started by rothbard, May 31, 2024, 10:34:37 AM

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I am about to put subfloor in.  I used the crawlspace design with 2x12 20' long joists (select structural).  Curious if anyone here did any levelling techniques on their joists.  I discovered after I already finished framing the floor that the crowning and warps in such long joists can lead to quite significant different from one to the next.  I think since I used SS lumber I can get away with planing them down quite a bit if needed (up to 3/4" or so), but also curious if anyone has just scabbed segments of smaller lumber on the sides to level the tops or shimmed them.

This is my first time working with subflooring.  But I have no interior load bearing walls.  Honestly don't care if it's not level, just curious just how bad I can get away with on uneven levelness of joist tops with 3/4" plywood.


I would leave it. Glue and ring shank nails to hold down 3/4 subfloor will go a long ways to pulling everything tighter. If you put a wood floor down it will hide difference even more.

If you feel like you have a gap between plywood and joist somewhere, you could draw it together with a screw, then glue will hold it once it's set, I doubt you will need to do that but could have it handy just in case.

My second floor 2x12 joists had a fair bit of variance to them - actual dimensional variability. I can subtly tell where the midspan beam is, but I am sure no one else can notice.


Sweet, thanks for sharing. 

I've already put some plywood in and now they're level within 1/4".  I threw some plywood on it and it had no trouble conforming.

Of course the next nightmare was toenailing the 2x12s into the sill.  I started with 4" of bearing on the sill and just from a single toe-nail half of it was lost, a pretty consistent outcome from any joist I tried it on...  seems when doug fir is dry it's about impossible to toenail into it.  Debating on whether it's worth the risk of more splitting to add hurricane ties.  I'm thinking if the joist runs out of bearing due to toenailing I guess I will just cut out a notch on the bottom eliminating the split and rest it on a doubled sill plate.

Edit:  Came up with new plan, will go back and measure bearing on plates.  Calculated minimum bearing for 16" o/c 19'1" 2x12 is  0.55 in of full 2x or ~0.825 in^2.  Seems incredibly unlikely any splintered to the point that only that much is left of the 4" bearing (6 in^2) but if so I will drill through the concrete blocks, bolt through them into a ledger board and rest the offending joists on 1.5" of bearing on a ledger attached to the CMU wall.