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Unread 01-28-2021, 04:58 PM   #45
nmeyers
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Join Date: Jun 2020
Location: Lenexa, KS
Posts: 36
subfloor concerns after sistering/between joist deflection

I'm finally done fixing the joists in my bathroom (originally 2x10 DFir/16OC/L416 deflecto), ended up double sistering each joist (the full length of room) with a 2x10 and a 2x6. I also added full height blocking midspan and at each wall. I don't know what the true new deflection is, I'm guessing somewhere between the original L/416 and the L/1249 I got by adjusting the thickness to 4.5".

I was going to go with 3/4" BCX plywood/membrane/tile but am now having some misgivings thanks to posts I've run into on here by CX and others indicating they don't tile over a single 3/4" plywood subfloor.

If I add a 1/2" underlayment as I've learned is optimal, I'll end up with a 7/8" transition between rooms (I had to raise the joist height in sistering).

It seems that large format tile is what is trending, and I just get a little queasy reading about between joist deflection causing failures...

Is there anything I can do to minimize deflection issues between the joists, aside from building up the floor with the second plywood layer? I was thinking that adding a couple more rows of blocking (flush with the joist tops) in between the 3 I just did would reduce the chance of any plywood deflection between joists, but I haven't seen that described anywhere on here.

Or am I overly concerned given the sistering I've done?

Thanks as always for your guidance.
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