Treehouse - cantilever and general planning questions

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Old 11-04-16, 10:57 AM
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Treehouse - cantilever and general planning questions

I am planning a treehouse for my little ones (7 and 10) and need to send something to the glorious Home Owner's Association for approval. I've attached a rough sketch of what I'm thinking for the layout and would like some advice on a few points.
1. I want to cantilever one (if not two) corners of the treehouse by about 24" from the corner posts. What do I need to consider? (The reason I want to cantilever is because I eventually want to enclose some of the space under the floor for use as a shed.)
2. I am planning on four 4"x4" posts, each 10' in length and buried 36" deep (with an additional 6" of gravel below that) and in concrete. Can I get away with these posts being only 2' deep instead with 6" of gravel below that? That way, I could get away with 8' posts instead of 10' if I go with a 6' height off the ground.
I was planning on the beams to be 2x8 PT lumber with the remaining joists, etc. in 2x6.
Thoughts? Advice? Thanks!
 
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Old 11-04-16, 03:53 PM
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I would not cut the burial depth of your posts just to save going from 10' to 8' posts. And, I'd consider setting the posts with compacted crushed stone instead of concrete. It's quicker as you can tamp in the stone and be ready to build immediately without having to wait for concrete to harden. And, it's better for the wood to not be in contact with concrete.

As far as cantilevering there are no codes for tree houses. Yes, 24" can be easily done if done properly (which isn't hard to do). I'm more concerned about your plan to somehow turn this into a storage shed. How do you plan to keep the water out?
 
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Old 11-04-16, 04:43 PM
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While I would build it as a free standing deck and pour footers and place the posts on the footers using post bases and brace the structure accordingly, I would not degrade the purpose of the fun place with a tool shed. You can cantilever 24", but no more. Make concessions for the tree to grow and sway in the wind as it could be devastating to the tree house once it makes contact with it.
 
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Old 11-05-16, 10:57 AM
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Thanks to you both for your thoughts.

I was just curious if 24" plus 6" of gravel under were deep enough, since I'd probably rather have my kids up only 6' anyway, but I understand your point.

As for the shed, it's on my hubby's wish list, and I figured someday we could frame in and enclose the space underneath the treehouse just to put the lawn mower and a few other items in. Two birds, one structure. It's my way of talking him out of buying a premade shed and making the kids play in it - as is his idea!

We would give the tree space for sure, especially since it is a tall pine.

Is my lumber big enough?

If I do footers, what dimensions should they be?
 
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Old 11-05-16, 12:03 PM
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The lumber you propose is fine. If you go much higher, graduate to 6x6 posts. Footers should be 12" in diameter and possibly 24" deep since you are in Texas. Use Simpson Strongtie post bases attached to each footer and to the post for stability.
 
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Old 11-05-16, 01:23 PM
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I have a problem with the deck design, maybe Larry or one of the others can help.

The floor is 8 x 10, being supported by beams only attached to posts.
The beams should sit on top of the posts and not be bolted to the sides. Bolts leave too much chance of shearing off in a worse case.
 
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Old 11-06-16, 08:09 AM
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By building this around a tree, you're making it a temporary structure as the tree will eventually grow too big and destroy it. Granted, you can allow room and make this years away but why not just build it freestanding away from the tree instead?
 
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Old 11-06-16, 09:30 AM
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I agree with SS. When my grandson was little I built him a 'tree' house minus the tree. Basically it was a raised covered deck with a slide along with a swing on the side. The bottom was a sand box. You could do something similar, larger than what I built utilizing the bottom for your shed.
 
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Old 11-06-16, 10:17 AM
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I would consider 6x6 posts and run them right up to the top of the railing. They will provide a much stronger attachment for the railings. I know it's a treehouse, but just attaching railing posts to the rim joist isn't allowed for decks anymore, and this being higher than a lot of decks, I would want very secure attachment for the railings.
 
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Old 11-06-16, 02:39 PM
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Thanks for all the added advice.
As for why around the tree... I don't have another place to put this, and building around the tree gives us a little more room. I would have to just make it smaller to avoid the tree. Plus, it's going to be the launching point for the zip line!
I can certainly see if there is any way to orient it in a different way to allow me to avoid this issue.
So if I use posts all the way to the top of the railing, wouldn't I then be bolting the beams to the sides of the posts?
 
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Old 11-10-16, 07:24 AM
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Would I be ok doing 10 foot 4x4s notched to receive the beams and then those posts extend up to support the rails?

And if I have to notch the posts, what's the easiest way to do that if all I have is a circular saw? Just eat away at it bit by bit back and forth?
 
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Old 11-10-16, 07:33 AM
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4x4s are often not considered sufficient these days, which is why Paul suggested 6x6 in post # 9.
 
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