Hello to all. I have a question regarding sistering floor joists? I currently have 2×10’s running 13′ between supports. I would like to add additional support for a slate tile floor, in particular where the refrigerator and oven are placed. I plan to finish my basement, and this is more piece of mind for me. My question is do the sisters have to be supported at both ends to be effective? There is about 4 inches on both ends that I can not access, however the other 12’8″ is good to go. Of course the 4 inches that I cant reach is where the supports are. The Joists are in great shape and this is probably overkill. Also what is the best fastening method. Thanks.
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What you are trying to do is add stiffness and limit deflection--for that you don't need to get all the way to the supports. I would be nice if you could, but you should be ok if you install through-bolts every 16 to 24", with an extra pair of bolts at each end. I would use 5/16" or 3/8" bolts. You can glue with some PL Premium if you want, too.
The existing floor joists may have a bit of a sag in them, so you might need to attach one end of your sister joist and work your way down the length, jacking as you go.
Note: I would not do this kind of engineering if your existing joists were in any way undersized. I'm just suggesting one way to increase the stiffness for joists that are properly sized and installed.
Unless the joist spacing is greater than 16"OC, you`re definetly going the overkill route....and this from the "king of overkill".
So long as you can spare the added height, I`d add another layer of 3/4" ply down for the subfloor and proceed as normal.
Just my two cents.
J. D. Reynolds
Home Improvements
"DO IT RIGHT, DO IT ONCE"
I agree with the Jaybird, I would add a load of polyurethane glue and 2 1/2 inch robertson srews.
Have a good day
Cliffy