Sistering To Correct Warped Joist... - Building & Construction - DIY Chatroom Home Improvement Forum

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Old 03-12-2013, 05:56 PM   #1
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Sistering to correct warped joist...

So... I have a joist under my bathroom that is warped for some reason. I guess it's possible that it warped due to moisture but it is not soft at all. I suspect it was just warped prior to installation and they installed it with the crown upside down. Most of the other ones are pretty true and level. The problem is, the floor sags about 3/8" over a 16" span from the good joists to the sagging one. I have some questions about correcting this. I was going to sister a new joist in to correct the sag.

Here are a few questions I have:

1) Should I jack up the existing joist in question before attaching the new joist or leave the existing one in place and knock the new joist in place?

2) What sort of fasteners should I use? I read I need to glue the new joist to the existing with wood glue and fasten every 16" O.C. Should I use nails, screws or bolts?

3) How should I remove the nails protruding through the decking/sheathing that are currently in the way of where the new joist will go? Cut them flush wish a sawzall?? Bend them flush with the underside of the decking?

4) I assume I need to remove my bridging...?

5) There isn't much running with the joists. There are two copper supply lines and some romex. Can I just detach these temporarily while I install the new joist? Maybe have my "assistant" guide them over the lines until I am clear to the foundation?

6) Do I need to go PT or just good ole fashioned kiln dried SYP?

Any other issues I am leaving out?


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Old 03-12-2013, 07:42 PM   #2
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Assuming that the original joist is not cracked and has no unusual up and down give to it (it's only warped) you could sister a straight 2x4 to it to establish a straight top edge, and that would be enough.

Use a sledgehammer to separate the subfloor from just the joist in question so to be level and to touch only the sister once that is in place.

I would use 3 inch ordinary nails every six inches, plus glue.

I would snip off the nails protruding down from the subfloor above.

The sister 2x4 can be cut into pieces to fit between the bridging without having to remove the bridging.


The good conscientious technician or serviceperson will carry extra oils and lubricants in case the new pump did not come with oil or the oil was accidentally spilled, so the service call can be completed without an extra visit.

Last edited by AllanJ; 03-12-2013 at 07:49 PM.
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Old 03-12-2013, 08:04 PM   #3
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Long Sawsall metal cutting blade and at least a 2 X 6 is the way I'd go.
No need for pressure treated.
Use constrution adhesive not wood glue.
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