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I'm working on my first big project, a 10x16 pergola. The long side includes three 6x6 posts 8 ft away from each other. There is another row of 3 posts 10 ft away parallel to those posts. All posts are set below the deck on concrete footers and deck posts. Posts are notched on top to receive 2x8 beams.

I have 2x6's running the 10 ft length underneath the beams to give some stability. My wife was wanting to hang a rather large swinging day bed from the pergola on the side where the grill is next to the fence. It will be about 5ft 6in wide and weigh about 75lbs. I would want to make sure 3 people will be safe on it just to be safe. So the overall load would be around 650-700 lbs. It would be attached at two different points across the length of the rafter above where the bench armrests would be. I can either make it hang from two ropes on one rafter or four ropes attached to two different rafters like the pictures I included, whatever is necessary. I was wondering what size rafters I would need to support that kind of weight if it's spanning 10 ft. I currently have 2x6's bought for the rafters but from what I read I will need something bigger.

I would prefer to avoid 2x8's just so the top doesn't get taller. Would 4x6's work as rafters? Thanks for the help. Pictures attached in link of ways I'm looking to attach the swing.

More photos

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  • What is "that kind of weight"? Please revise to list the expected weight of the device and occupant(s) as well as information about mounting locations, etc. It matters whether you have two anchors 6 feet apart or one in the middle.
    – isherwood
    Sep 27 '20 at 18:39
  • What is the spacing on the 2 X 6s ? 16" is pretty typical . Sep 27 '20 at 20:32
  • Updated the post to approximate weight and mounting. I also attached a couple of screenshots to the link of different ways I could attach the swing. Havnt decided on spacing but was either going to do 12 or 16. Sep 27 '20 at 21:11
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    So unrelated to your question, did you consider any kind of diagonal bracing for this? Sep 27 '20 at 21:14
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I think you'd be fine hanging the swing from both 2x6's. (I don't see any reason you wouldn't use both.) Southern pine 2x6's are OK up to 9'11" for joists if spaced 12" on centers. But those numbers are based on limiting the amount of deflection of the joist, so the floor isn't springy. In this way, a little deflection isn't going to be a big deal, in fact a lot of those swings have a spring in the support so they have some give.

If you sink four eye bolts into the bottom of the 2x6's, two at each end, and put say 1' of chain on each eye bolt, and use a threaded link to connect that to the chains that the swing hangs from, it should be more than strong enough.

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  • Something like knee braces? Or something larger going diagonally across the top of the structure? Was going to add knee braces to corners posts at some point, just havnt figured out exactly how to do it yet. Wasn't planning on any diagonal bracing across the top though. Sep 27 '20 at 21:17
  • It looks like the whole thing is rectangular and could be prone to racking, which could be really bad. I was thinking some braces between the posts and beams and between the posts and the rafters. Sep 27 '20 at 21:30
  • Yeah I think I will do that. When I push the posts towards the grill it doesn't budge, but when I push the direction going towards the gravel below the deck it moves a little, not a lot though. Sep 27 '20 at 21:36
  • Any recommendations on how to attach rafters? Pocket screw/toe nail or put long structural screws through the top all the way through to the beam? Sep 27 '20 at 21:53
  • I like long structural screws for rafters. Use a crazy long drill bit to predrill with two pieces of ply sandwiching the 2x so that you start centered and stay dead plumb. Sep 27 '20 at 22:00

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