Best wood variety for long, outdoor beam

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  #1  
Old 12-18-15, 05:28 PM
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Best wood variety for long, outdoor beam

I'm looking to make a swing set by hanging a beam between two, large trees. I've already been brought up-to-speed on how to secure the beam to the trees without restricting sway or having it break the beam.

The trees are about 18' apart. I was really hoping for something like 14', as 16' beams are easy to find. I've got four types of wood available nearby that should do OK outside:
  1. Pressure treated pine. For this one it's no big deal that I can't find it longer than 16" because I already planned on joining 2-3 layers of 2x6 or 2x8 to control the warping. since I'll already be gluing and screwing, I could just splice together the layers with shorter boards at staggered spots.
  2. Cypress. I found a mill nearby that I can get 2x6s, 2x8s, 4x6s or 4x8s from and they may be able to give me a 20' piece depending on what they've got. Otherwise, I can do the same as the PT pine and splice together a couple layers of 2x?s.
  3. Kiln dried cypress. Longest length is 16' so I'd have to do the spliced 2x? layers here to make a longer beam.
  4. White oak. Another mill, same situation as the cypress - availability of one, solid beam would depend on what they have.

So what's the best material for this application? Best way to build the beam? Consider that the hardwoods won't likely be old growth so I'm probably not getting good heartwood. Should I worry about them warping or rotting? For that span, considering the light, intermittent load, would a 6" beam work or should I go to 8"? Should I add additional support with cables and turnbuckles holding up closer to the center of the beam?
 
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Old 12-18-15, 05:37 PM
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Absolutely do not splice anything. Call a real lumber yard and get longer length lumber. Its readily available at any good lumber yard. SYP is probably what you should use.
 
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Old 12-18-15, 05:42 PM
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By that, I take it you mean not to use a length of board that can't span the trees. Would you advise against joining a few layers of 2x to make the beam to control warping as I mentioned with the pressure treated SYP?
 
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Old 12-18-15, 06:12 PM
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I'm not going to advise anyone to make their own glulam, no. I hope what you are doing is going to be safe. Peoples lives will depend on it. That thing comes down and hits someone in the head and it'll be all over.
 
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Old 12-18-15, 06:21 PM
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Splicing looses strength. You really need to special order something.
 
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Old 12-18-15, 07:52 PM
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I appreciate the thought. That's why I'm here.
 
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