High there. I’m building a fort for the kids. I’ve sunk 4 treated 6×6 posts that are 10 ft in length. 5 foot deep holes, gravel on the bottom, then set in concrete, with about 6 feet of the post sticking out. Distances between posts are 11 feet on center by 8.5 feet to hold a platform that will be roughly 10×12. My question is this: will double 2x10s beams be strong enough to span the 11 foot distance (plus 6 inch cantilever on each side) between the posts?
many thanks
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Replies
Honestly the only person that needs to answer this is a architect or a engineer. a majority will depend on lumber size, grade of lumber and a fastening system. Their is a lot of liability for someone to say "doubled up such an such ought to be good nuff". Not trying to sound like a jerk here, just remember it's KIDS that will be playing on it. the only advice I'll give is this, over build it. They're could be a lot of dead load and live load up their after everything is said and done. You do not want the floor system to be "close enough".
No.
Ok, that seems like a fairly resounding "no". I would rather just use the 4 posts rather than any more. How about 2 or 3 2x12s?
There is plenty of enginerring already available out there.
If you look at the deck span tables they would say a pair of 2x10 SYP in a beam is enough for a 40 PSF load in a 11x11 deck.
Our deck (fully stamped and inspected) is 12x18, supported by 3 doubled 2x10s in the 12-foot direction. Been standing about 25 years now and no sign of problems.
For a 50 psf load you need double 2x10s run in the short direction with 2x10 joists run in the long direction at 2' oc.
Or you need double 2x12s run in the long direction with 2x8 joists run in the short direction at 2' oc.
I would consider 4x lumber all around with the edges rounded or beveled to minimize splinters. With the beam run the short way, you'd need 4x8s all around. With the beam run the long way you'd need a 4x10 beam with 4x6 joists.
Great- thanks so much. If 2 - 2x12x12's are good, should I just run 3 of them the long way over the 11 foot span? I guess then if I do 3 on top of the 6x6 posts, I will be using a Simpson connector vs notching the post......
The short answer is, "yes, "
The short answer is, "yes, " that will be plenty for a play structure.
The Cantilever helps..
The cantilever helps offset some of the load on the span between the beams.