help with sistering joists!


Old 07-16-05, 08:20 PM
Thread Starter
Join Date: Apr 2005
Posts: 42
help with sistering joists!

hello everyone

doing a complete gut-rehab on the second level of my home, and am now in the process of sistering the floor joists under the BA. these joists are 2x8, 16" oc, and the distance from the the rim board to the interior LB wall where they end is 11' 6". however, there is another interior wall (LB? i'm not sure) 8' from the rim board. so i'm not sure if the span is the 8' to what may be the first support, or if the span is the complete 12' to the end of the joist.

in either case, the prior owner notched these joists to run plumbing, so i needed the sister them. i went out and bought full-length sisters (12' cut down to 11' 6"), and glued them to the existing joists, then used 2 rows of 1/4" by 4" hex bolts with 1/4", 3/8", and 1/2" washers under both the bolt and the nut, spaced every 16".

however, after i sistered 2 of these joists (there are 5 total, so 3 left undone), i noticed that the crown in the lumber made the middle 8' of the new 11'6" joist about 1/2" higher than the old joist. so i stopped my work, and am hoping for some suggestions as to what to do.

can i plane the new joist 1/2" to bring it level? or is that compromising too much strength? i had planned on laying 3/4" t&g osb subfloor over the joists, then laying ditra right on the subfloor, then ceramic tile.

what do i do about the un-sistered joist, given that the new lumber also has a crown? i had bought several 2x8s, and it seems that even the "straightest" of them still has a crown of approx. 1/2" over the 12' length. just to see, i had tried toenailing a new joist into the old one to see if that pulled the new one level - however, that didn't work.

all the joists are supported at either end by a top plate of the 1st floor framing. one end by the top plate of the exterior wall, the other end by the top plate of the interior LB wall 12' from the rim board.

thanks anyone for their help with this...i'm really stuck
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Old 07-18-05, 07:40 PM
Join Date: Dec 1999
Location: South Dakota
Posts: 3,140
Sistering joists

All lumber has a crown in it. That is what gives it the strength. However, in your case, it is working against you. I would probably try to flip the over and put the crown down. Secure it in the middle first so they are level, then pull each end down and nail in place then put in your bolts last. Give this a try.
Good Luck.

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