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shadow700

Treehouse on a free-standing 10'x10' deck 8' off the ground

shadow700
13 years ago

I am thinking of building a freestanding 10'x10' deck and "treehouse" about 6-8' off the ground and am looking for any special considerations I'll need to take into account. Below is the basic narrative for the project and the questions that I an looking to determine answers for. If anyone can provide some insight into any of the questions, I would appreciate it.

On top of this deck will be a ~6' high treehouse (while we have a nice treed area, none of them are candidates to support a treehouse on their own, so am I just going to build one on a raised deck).

I think I am going to use four 6"x6" posts set in an 8'+ square to support two 10' sistered 2x8 beams. The piers will be 12" across, 36" deep (below frost line here) and have bolts placed when the concrete is poured or wedge anchors placed after curing. Metal brackets will be bolted to the concrete.

Question: What is the appropriate method for connecting the posts to the brackets? Do I use nails or screws? I've always used nails, but I've also never done a tall, free-standing structure like this and didn't know if it called for something else.

Question: Is there a preferred bracing member configuration between the post and beams for this design?

One top of the beams will be a 10'x10' platform built of 2x8" joists.

Question: Assuming 12" oc install, it's 11 joists. 16" oc, it's 9. For the cost of two extra joists, is there any reason not to go 12" oc?

On top of that, a 6' tall house will be constructed. I am still working on the design, but it not going to be anything too "out there" (else the kids will be fully grown before I finish it!). If anyone has any thoughts on a design or design elements, I would love to hear them.

Thanks in advance for any comments.

Comments (3)

  • fnmroberts
    13 years ago

    I don't entirely follow your description. But, understanding what you are planning and having built a free-standing pergola, can offer some comments.

    Are you setting the posts in the ground surrounded by concrete or pouring a concrete footing, then attaching the posts? My pergola is done the later way. I have no bracing between the posts and rafters. There is slight movement atop when it becomes necessary to go there. So, I would advise sinking the posts and bracing the corners for maximum stability. A 45 or 30/60 (4x4) would be fine unless you want to create a solid bracket.

    I'm sure 16" oc will be fine - your house is built that way.

    I used hardened screws plus galvanized carriage bolts and lag screws

    My pergola is for an entirely different purpose but design considerations are similar. The last photos are schematics of mine.

    Check local building codes too. Good luck.

    Here is a link that might be useful: Freestanding Pergola

  • builtbymac
    13 years ago

    Q: What is the appropriate method for connecting the posts to the brackets?

    A: Use the fastening hardware specified by the bracket manufacturer. For ex, a Simpson AB66 requires (8) 10d nails, whereas a Simpson CBSQ comes w/ it's own SDS screws. Whatever brackets you buy, research their fastening specs.

    Q: Is there a preferred bracing member configuration between the post and beams for this design?

    A: If you're not going to run the posts down into the concrete - For stability, I would run 2x4 cross bracing in both lateral directions. From the top of one post down to the bottom of the adjacent one and alternate the other side. You end up w/ a giant 2x4 'X' between each set of posts. (5) 16d nails per end, staggering them to avoid splitting the end of the 2x4.

    Q: Assuming 12" oc install, it's 11 joists. 16" oc, it's 9. For the cost of two extra joists, is there any reason not to go 12" oc?

    A: It depends on the flooring system of your tree house. If the flooring can safely span 16", there's no need to go 12". No reason "not to go 12" except for it's a little more (unnecessary) work.

    Mac

    Here is a link that might be useful: My deck blog

  • shadow700
    Original Author
    13 years ago

    Thanks for the responses.

    I think I am going to use the CBSQ on the piers. The ground is sloped a bit in this area, so I'd like to bring the piers out of the ground a bit and make the tops level with each other. I'll have to measure, but I think the elevation difference over 8' is about 18".

    Is there any problem bring the piers up that far out of the ground (assuming they are still at least 36" into the ground)?

    Should I use a higher PSI concrete in this case?

    As far as bracing, I was thinking x-es on two sides and then inverted v-s on the other two (front/back). This way, we could walk under the structure more easily.

    Thanks!

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