Sistering joists to increase live load

[mykcuz]

I'm sorry, but the screws aren't simply holding two pieces of lumber together, they are creating a beam and sharing shear loads as weight is added and removed above. (Live load)

If using framing nails, you would have to glue and then nail rows of 4 nails every 16" from both sides, typically on a triple(yes I know he's discussing a double), whereas a structural screw would be installed in pairs of 2, sometimes 3, with spacing varying from 16-24" from inky one side.

So yes, you could substitute deck screws and use 4 times as many plus washers(which aren't actually spreading the load properly, or you could simply pickup a box of the correct fasteners with washer heads, and have the proper strength for the life of the floor.

Again, speak to an architect/ engineer for 30 seconds and you'll have your answers.

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[cx]

Mike, if the two pieces were not to be glued together I'd be more inclined to agree with your argument, but I don't recommend anyone ever do any structural sistering without using and adhesive between the pieces. The mechanical fasteners serve as gluing clamps as well as adding some structural value after the glue has cured. Not only does the glue provide the majority of the structural value in that application, but also virtually eliminates the problem of creep experienced with mechanical fasteners alone.

The decking screws are also more prone to breaking than are nails or some other structural fasteners, but I've never experienced that when using them for joist sistering.

My opinion; worth price charged.

[PC7060]

Again, speak to an architect/ engineer for 30 seconds and you'll have your answers

As one of the engineers you reference, the word I would use if someone recommended SDWH screws for this application would be “overkill”. Many would argue my approach with screws and glue is also overkill.

The OP is simply sistering a second joist to improve stiffness of the floor to meet requirements of TCNA so we are recommending a cost effective method to meets that requirement.

Agree with you completely if we were specifying fastening schedule for main beams but that’s not the case here.

And in line with CX tag line....

Disclaimer: I am a structural engineer, but I'm not your structural engineer. Check with a local PE before you try anything I suggest.

(On this we agree, Mike! )

[ranchopedro]

Originally Posted by Damon

What do you recommend?

Start here and read a few of these
https://www.eng-tips.com/search.cfm?...earch&q=sister
I will guess a few LVLs are in your future
Dont go blindly ...get yourself a structural engineer to cast an eye (wont cost much)

If you dont know fasteners well GRKs are awesome, come with a bit, and will not cam out
For your task R4s may suffice ...with a nice impact
https://www.grkfasteners.com/

[PC7060]

Originally Posted by Pedro

If you dont know fasteners well GRKs are awesome, come with a bit, and will not cam out. For your task R4s may suffice ...with a nice impact

Them’s some nice screws, Pedro.