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Sistering a rotten floor joist

468 Views 1 Reply 2 Participants Last post by  Nealtw
Hi there. I have identified a floor joist that is pretty badly rotten - it's also nearly completely cut through at one point by a duct (thanks HVAC guy!). I don't think it's providing nearly any structural support for these two reasons, so I would like to sister it.

I may not be able to properly remove the rotten sections of the existing joist due to accessibility issues.

My question is: would the sister beam begin to rot (or rot prematurely) when in direct contact (bolted, glued) with the existing rotten joist? I'm just wondering if the fungi might still be present and able to invade the sister beam. The house is over a hundred years old so I'm not sure at which point the joist started to rot, and if its deterioration has stopped or is still progressing.

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Any time we leave questionable wood we paint it with the same copper treatment as treated lumber and in your case I would use a treated timber for the sister.

I would not glue it with what ever you use, there will be a moisture difference and shrinkage. Glue can prevent that movement and cause cracking in the new timber.

3 nails 16" OC is all that is required.
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