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Unread 01-17-2019, 08:15 AM   #8
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Join Date: Sep 2018
Posts: 210
I don't like taking chances. Just wish I'd realized my mistake sooner. The tile isn't down yet but the tub is set in a layer of cement and I'm afraid messing with the joists is going to crack that base. I can't remember how I figured that the floor was good enough, might've only used the span of the bathroom floor instead of span between supports or figured that 3/4" plywood and ditra would do it. The user name and pic are appropriate.

Luckily, what's below the bathroom is the basement and I have access to the entire span of the joists from sill to the support beam running down the middle of the house. I'll have to get around a bunch of plumbing and electrical and tare out a plaster and metal lath ceiling but I hate having a finished ceiling in a utility-type space anyway.

So the plan is (and tell me if I'm planning something stupid, please) sister the two single joists in the main span of the floor with 2x8 doug fir lumber. You can see them in the photo above. There's one about under the right wall but it's more out of the way and there's a heater pipe next to it. Use the full 12' of lumber and lay the ends on the sill and support beam like the original joist. Glue and screw the new lumber to the old, 3" construction screws in pairs top and bottom 1.5" from edge of beam every 8" and PL Premium adhesive or similar. This thread is my reference: The floor is planks with plywood glued+screwed over them so I can't screw the planks to the new joists without taring it all up but I'll try to get some subfloor adhesive at the top to keep it stable and fill the void.

The sisters will need to rotate upright and I don't want to disturb the existing floor (and everything on top of it) too much so I might notch them so they're loose between the bottom supports (beam and sill) and the floor then shim them up to hold them in place. They're not supporting the floor, they're reinforcing the old joist. Does that sound reasonable?

If I go out today and buy the 2x8 doug fir lumber today from a place that keeps them indoors, how long do I have to keep it in my basement aclimatizing before I can use it?

Thank you for your help.
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