This is really a 1.5 part question. The first half has to do with whether it's okay t use single post for one side of a swingset (the other side will be attached to a play structure). I've seen some designs with 6x6s and maybe that's beefy enough when sunk 3' and concreted in. Any thoughts about that would be appreciated. It seems like the top might swing a little and the forces (especially if an adult is swinging) could loosen the concreted block in the ground even if the post doesn't sway.
The 2nd and primary question is whether I can save money on a 6x6 post and make build one up with 4 2x4s. It will also be easier to handle (bring home from home depot) and cut and I can get pressure treated 2x4s in lots of lengths including 10ft so I can sink it into the ground far. I realize it won't be 6x6 (5.5" x 5.5") but it'll be 5x5.
And because it's hollow it won't be as strong as a 6x6 but should be much stiffer than a 4x4. I guess I'd need to cover the top so water doesn't get in. I guess I could stiffen it up by putting a few blocks internally as well.
Any guesses on the strength of this approach and downsides?
Another set of options is (1) attaching the post to the garage so that it is more stable to the back and forth motion when swinging or (2) attaching the horizontal beam directly to the corner of the garage.