I just hung a new porch swing (porch ceiling is finished). I was wondering if you would suggest reinforcing the attic joist as a precaution. If so, will screwing a few 2x4's perpendicular over 3 joists (the center joist being the one that the swing is on) suffice? Or is that a waste of time? Should I instead sister a joist to the affected joist? Any suggestions are welcome...it is a 5 foot, heavy swing so I'm a bit paranoid. thanks!
If the swing goes back and forth perpendicular to the joists then do the right angle brace. The brace is very strong horizontally in compression or tension but I doubt that sistering will add much rigidity in the horizontal direction.
A person swinging I guess counts as an impact load so use screws.
You could also put a plank along the top of the joist so you make a "T" cross section.
Or, using 1x3s 22-1/2" lg, put something like bridging at the bottom of the joist that extends to each of the two joists alongside the swing one. That way sideway forces on the bottom of the joist will be shared between three joists.