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Sistering Joists Effectively

Sistering Joists Effectively

Sistering Joists Effectively

I am renovating a couple balconies because the existing 2x10 joist from ext to int are decaying. I plan to sister a joist in and am having a difficult time determining how to connect the joist effectively. I can't connect the joist directly to the decaying joist because I cant assume the "bad" joist will transfer the load. However, I also have an issue nailing directly to the diaphragm because I have an 1 1/2" of concrete above the 1/2" plywood. Any ideas on how I can connect the new 2x10 joist and get any values???

RE: Sistering Joists Effectively

If you have a bad joist and want to leave it in place, do not rely on it at all for strength. Just install a new joist full length if you can do that. Make sure that the new ones are PT.

But, more importantly, correct the reason for the deterioration of the joists in the first place. With a 1.5" concerete overlay on top with plywood underneath, I would expect venting problems or the total lack of it (Have seen a lot of this in Apt buildings). I would also expect the plywood over the joists to be aqs deteriorated, if not more. Check it out if you haven't done so already.

Mike McCann
MMC Engineering

RE: Sistering Joists Effectively

Do the old joists perhaps go through the exterior wall???

If so, the repair can be complex or easy.

1. Complex - you will need to te tear out the ceiling and re-install.
2. Simple - cut them off, install a ledger and posts

Good luck. Done a bunch of them either way!!

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