# swingset beam, 4x6 or sister'd 2x8's?



## D270 (Mar 27, 2011)

Hi,
I see many playsets with a 4x4 across the top and holding 3 swings, a 12' span.

This doesn't seem like enough....so I was looking into a 4x6 beam out of cedar (mainly due to not worrying about the hardware reacting with the PT).

Instead of a 4x6, would two 2x8's or heck, 3 2x8's be stronger and not twist?

I would imagine if I went way over the top and put 2x10's up there, pretty soon I'd have to start worrying about the actual beam weight!

Thanks for any opinions!
D


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## D270 (Mar 27, 2011)

any opinions? Thanks


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## preacher01 (Aug 13, 2011)

I built one with 2---2x8's pressure treated 12' long 20 years ago and just took it apart because the girls have grown up and I needed the wood elsewhere and I never had any trouble with it. I had 3 swings on it with a slide. Hope this helps you out.


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## Daniel Holzman (Mar 10, 2009)

It is a common concern that using larger dimension lumber will "weigh more", and this will cause sagging, or some other concern. This is never the case. The strength of a structural element increases as the cube of the depth, so a 6 inch deep member of the same material, with the same width, is 8 times as strong as a 3 inch member. The weight of the material is never a problem in residential construction. The reason that larger structural members are not used is higher cost, and the greater depth can interfere with ceiling height or other dimensional constraints.

As for a swingset, the actual physics of swinging cause surprisingly large forces on the structural elements. In particular, if a 100 lb person swings, it is possible to exert up to 200 lbs of force on the supporting beam. In additional, you get twisting forces which can affect the connection design between the swing and the beam.

It is for this reason that I generally recommend that you "borrow" a proven design from a swingset manufacturer rather than wing it with your own design. When you "borrow" the design, make sure you look at everything, including the hardware (should be hot dipped galvanized or stainless steel), the connection details, and the species of lumber used, in addition to the size of the structural elements. I know this sounds like nerdy engineer geek talk, but you are not going to find a handy code book to walk you through this project, so it is a good idea to use someone else's proven design.


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## D270 (Mar 27, 2011)

Thanks, all good opinions. I have seen both a 4x6 and even 2, 2x6's....I would like to increase the saftey margins that's all. 

For the beam I'm planning to use cedar so as not to worry about the hardware and the possible affects of PT wood....3-4x the cost though.

All suggestions are welcome!


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