Replies

1. 
   florida | Dec 06, 2019 12:43pm | #1

   The 6 x ^ each have a capacity of about 13,000 psi straight down so no worries there. You'll need to pour concrete around them to stop the lateral loads though. Two 2 X 10" s should be fine but if not just add another one.

1. 
   rpm2522 | Dec 07, 2019 07:45pm | #3

   Ok thanks

2. 
   ktkcad | Dec 07, 2019 05:13pm | #2

   My last lumber swing set had two main posts (5" logs) per end. These 'clamped' around the beam log and lagged through it. Then they were buried in 30"-36" x 12" dia. of concrete and still managed to crack those footings. Good thing we had heavy clay soil to hold them together. Just saying your beam to post connection will be critical because of the lateral loads. And the longer the beam, the higher the lateral loads. Don't let 'moment' bring you down.

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   rpm2522 | Dec 07, 2019 08:01pm | #4

   Ok thanks, today I dug two 4’ Holes for the vertical 6x6 support posts. I have concrete to fill them with tomorrow. I’ve also read that spreading roofing tar on the part of the post in the ground allows the concrete to stick to something better than wood and also protects the wood longer. I’m also going to drill a few lag bolts partially in the bottom of the post so the concrete hardens around screws attached to the post.
   I’m putting two 2x10x16s together for the main beam. I’m going to cut the tops of the 6x6 posts halfway in at the top (half-lap joint?)so the horizontal beam can sit on the post. I’ll also add 45 degree supports.
   Do you think any of this sounds unsafe/unreasonable? Thanks

1. 
   florida | Dec 09, 2019 08:44am | #6

   Sounds fine. I'm assuming you're using treated wood? I would not put tar between the beam boards though unless you want it eternally dripping on your kids.

3. 
   suburbanguy | Dec 08, 2019 05:39pm | #5

   Those two 2 x10's fastened together are going get water between them and rot.--from the inside!! I fear that no one will notice until it fails. I'd spread roofing tar on the adjoining surfaces before bolting them together (or to the posts, depending on how you're constructing it). ....and just for good measure, I'd caulk the joint with a professional grade caulk. Mulco caulking comes to mind here in Canada. It is amazing and so easy to use. Find what window installers or aluminum guys use in your area.
   Alternatively, you could cut some roll roofing or ice and water shield and lightly tack it over the built up 2 x10's so that they shed water. (I did that on my deck joists and beams, so at least the supporting structure will never rot.)

4. 
   suburbanguy | Dec 09, 2019 09:55am | #7

   Looks like someone posted and then deleted it.
   Pressure treated wood does rot and surprisingly quickly sometimes. Don't worry about dripping tar. A thin coating of Wet-Stick dries by evaporation and won't drip on your kids. (I used it on the end cuts of my deck joists... in addition to the liquid treatment that keeps the inspector happy.) I store stuff under my deck and I'm in under it all the time.
   Too many people comment based on their speculation.

1. 
   rpm2522 | Dec 09, 2019 06:04pm | #10

   Thanks, I didn’t think of that as a potential weak spot.

5. 
   florida | Dec 09, 2019 11:02am | #8

   I posted not to put tar on the beam and my 50 years experience backs me up. It s a dumb idea that wouldn't work anyway. Creosoted post are impregnated with it and they rot just fine. I didn't delete my post either, FH has decided it doesn't like me anymore so my posts disappear at random or take a day or so to appear.

1. 
   rpm2522 | Dec 09, 2019 06:13pm | #11

   Thanks for your input. Is 16’ too far of a span for the horizontal swinging beam? That’s the two 2x10x16s.

6. 
   suburbanguy | Dec 09, 2019 12:07pm | #9

   I have no idea about roofing tar on the posts that are anchored in the ground. My suggestion was strictly about its use between the two 2 x10s to prevent rot. ...and my experience says that it will DELAY moisture from rotting that interface. Its a liquid, containing volatile compounds that flash off, leaving a flexible coating. It would become tacky even during the time that he stopped for lunch. It will definitely NOT drip on his kids. You're thinking of a much different product than Wet-Stick roofing tar, perhaps something that is troweled on, rather than brushed.

7. 
   suburbanguy | Dec 09, 2019 07:06pm | #12

   I have no idea what a "surfer swing" is. (I originally commented because of my concern with the development of hidden rot and the potential for failure.) No idea about the location or number of chains (or rope) that holds whatever swings to the 2 x10s. No idea of the number of kids (or adults) that might end up horseplaying on it at a party. No idea about the end connections (beam to posts). All sorts of lateral forces... ...For example if you through bolt the 2 x10s on either side of the posts, that is a completely different situation than a built up beam 2 x (2 x 10s). There are many ways something like this can fail. I was a P.Eng before retiring and really don't want to make structural recommendations on something I know nothing about. There's an old engineering saying. "When in doubt, make it stout, out of things you know about". Best to copy one that you've already seen that has been "well used".