DIY Home Improvement, Remodeling & Repair Forum > DIY Home Improvement > General Home Improvement Discussion > sub a 6x6 for an 8x8? treeless tree house




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Old 04-03-2009, 08:58 PM  
Philphine
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Default sub a 6x6 for an 8x8? treeless tree house

i've been wanting to try this treeless tree house idea but can't find an 8x8 piece of lumber to be the main base/pedestal.

The tree-less tree house UBuild....step by step

i've been wondering if i could use a treated 6x6 instead. let me say i mean to make a slightly smaller platform (about 6'x6' instead of 8'x8') and shorter height (about 5' off the ground instead of 8'). i also don't plan to put a roof on mine (so not as top heavy), and i want to make two platforms with a swing set bettween them so they'd kind of brace each other a bit. i'm hoping those things might let me get away with it.

should i keep trying to find the 8x8, or do you think this would be ok? thanks for any help.



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Old 04-03-2009, 11:04 PM  
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What you're asking is actually a fairly involved engineering question.

What you need to do is calculate the "strenght limit" in "buckling" for a column that is fixed (or "clamped") at the ground, but is free to move in any direction at the top. This web page explains the calculations, and if you use Google to look up terms you're not familiar with, I'm sure you could do those calculations:

http://www.engineers.auckland.ac.nz/...ling_Notes.pdf

However, I think a better solution would be to make an 8X8 out of five 2X8's. The critical thing is that the five 2X8's must not be allowed to move relative to one another, so that means you'll have to glue them together (flat to flat).

The situation is similar to that of a deck of cards. It's almost exactly 52 times harder to bend a deck of cards as it is to bend one card. However, if you were to glue all the cards together so that the cards couldn't slide relative to one another, then entirely different equations come into play, and it becomes as hard to bend that deck as it would be to bend a solid block of wood of the same size and shape.

The reason for this is not hard to understand. If each card is allowed to move relative to it's neighbors, then the cards on the convex side of the bent deck don't have to stretch to bend the deck. But, if the cards are glued together, the ONLY way the deck will bend is if the cards on that convex side actually get longer (that is, STRETCH!) to accomodate the changing shape of the deck. Since paper is actually fairly strong in tension (which is why drywall is fairly rigid considering what it's made of), the deck becomes very much harder to bend (and therefore is VERY MUCH STRONGER). Consequently, if you don't glue the 2X8's together, the beam you'd make would be 5 times as strong as a 2X8. But, if you glue the 2X8's together so they can't move relative to one another, the beam you'll make will be as strong as an 8X8. Hope you followed the explanation.
(I graduated from mechanical engineering in 1978.)

Now, it's intuitive that the strength of the glued joint has to be as strong or stronger than the wood for this to work. Otherwise, there could be slippage at the glued joints that would make the bundle of 2X8's weaker than an 8X8. If it wuz me, I would glue the 2X8's together with LePage's PL Premium construction adhesive, which is the strongest wood glue I know of. Then, put chains or aircraft cable around the bundle and use car scizzor jacks (which you can get for $1 each at any auto wrecker) to tighten the chains or aircraft cable around the bundle of 2X8's to clamp them tightly together, and let the glue cure that way. I'm guessing 7 chains evenly spaced every 2 feet along the 12 foot long bundle would suffice to provide uniform clamping pressure along the entire length. I'm thinking a 12 foot tree trunk with 4 feet anchored in the ground (or set in concrete) and sticking up 8 feet.

As long as the glue you use forms a bond stronger than the wood itself, then you can make an 8X8 by gluing 2X8's together. Clamping the 2X8's together as the glue cures increases the strength of the bond. PL Premium uses a moisture cure polyurethane, so any moisture in the ground shouldn't weaken the glue but make it stronger. However, read the fine print on the tube or check with LePage's to ensure it's approved for use underground.



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Old 04-04-2009, 07:35 AM  
inspectorD
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Or you could just find an old used telephone pole and cut it down....or not.
I have seen them on craigslist and sometimes the power company will sell you the used ones.
Unless you have a degree in engineering...I would stick to what you know.

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Old 04-04-2009, 08:53 AM  
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Hello Philphine,

I'm from the Louisville KY area too. 84 lumber may not stock 8x8 but they can get them. I talked with the 84 on Dixie Hwy and they can get them so that means that any 84 in our area should be able to get one for you.

Seeing a picture of your plans, or the project, would be interesting if you're able to post up!

Thanks, Doug

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Old 04-04-2009, 02:58 PM  
Philphine
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thanks everyone. i didn't think of trying to glue 2x8's together, but i guess it could work. i tried looking at the stress calculations but i kept getting geometry class flash backs and breaking into a sweat fearing a pop quiz. i appreciate the attempt at trying to "learn me somethin'" though.

inspector d, i kind of though about a phone pole. i think that might be close to what they suggest using, but i'm thinking something with flat sides would be easier to work with and line up with an identical structure. it was also suggested to look for railroad ties, but they always look so bad. i guess being that this will be part play/swing set i'd need to worry about splinters and rr ties look so roughly hewn.

jdougn, i knew 84 could get them, but when i first started looking into it the price they gave for ordering one was so far beyond what i paid for the 6x6 (used a few on my deck), something like $160. guess i may have to if i want to do this.

i only have some basic sketched up plans, more for dementions/placement in the yard than the structure it's self. the reason i can make it smaller and shorter is because the actual goal is to make a base/support for an outdoor home theater screen (also the reason i want to make two and link them). i'm thinking i can make something that can serve some purpose when a screen isn't up, and not just be a big wooden frame in the yard.

thanks again.

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Old 05-28-2009, 02:18 PM  
rvblevins
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Was wondering if you ever got yours built. I am in the process of building the same thing - I planted a used Telephone pole last fall and put the platform on a month ago and have been bldg a treehouse on it since. Problem I am experiencing is the platform pivots on the pole. I followed the instructions to a "T" and is still pivots - so I was wondering if you hade built yours - did you experience this issue, and how did you solve it. Of course if you went with the 8X8 idea, then probably not

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Old 05-30-2009, 05:57 PM  
Philphine
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sorry this is lagging i just saw the thread notice email,

but no, i never built mine. i still mean to since it's part of a bigger plan (the starter holes are even dug so i don't have to keep measuing it out when i forget where it's all going), but i'm still holding out to find 8x8's (though i did get another glue together suggestion, but with a 6x6, a 2x8 and a 2x6)

what you're going through is why i thought a square side pole would be better, but i was thinking with a round pole i'd probaly try to notch two flat sides into it for the two centermost joists.

also my plan was to make two smaller ones and have like monkey bars and/or a swing joist bettween them, with possibly a ladder for the bars on each side, so i guess that might make them a little more stable too (and having the two kinda offset legs was another reason i though i could get away with a 6x6).

what came to me just now while i was typing this is that it might work for you too, as long as you feel the structure it's self is basicly stable. if you plant the ladder also and connect the ladder top firmly to the side of the house, it ought to keep it from moving

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Old 05-30-2009, 09:30 PM  
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I don't know as I would want a 15' tall structure supported by one post. Too much risk, especiialy if kids are up there

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Old 06-08-2009, 11:47 AM  
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I'm just starting out with the same Ubuild plans. I have the pole cemented in 5' and will start building next week. Regarding the plans, has anyone found any problems with them? My biggest concern is with the hip roof. I'm quite surpurised that with as detailed as the first part of the plans are, that they fail to follow through to the roof. For those that have completed the roof on their project, do you have any helpful hints on constructing it? Also, does anyone have any pictures to post along with this thread?

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Old 06-08-2009, 05:56 PM  
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Well..... The joists are lagged to to post 6" with 4-1/2" going into the center. You can't screw into the top or bottom 2" of the 2x8's (for compression and tension), so you are limited to 3-1/2" space. This multiply times two, and the smaller stub joists you could screw higher or lower. Still, with 8-4-1/2" lags going into a space of 5 vertical inches, I'd want a husky telephone pole. A 6x6 would not work with all 8 lag holes and each 4-1/2" in--- leaving 1" of untouched wood.

On the diagonal braces, 8" lags going ? into center, all in the same plane.......

I'd pitch the floor for water run off. Add another 2x8 on each top for the roof, add some collar ties so the roof doesn't spread.

Put the post on gravel and back-fill the concrete with gravel. (To stop frost jacking or heave) Pour a footing under the post and fasten them together. As well as put plastic around the pole, underground, to reduce frost heave from the ice lenses. Google that.

Building a deck: expert advice from ... - Google Book Search

How Aggregates Prevent Frost Heave

SULIS - Sustainable Urban Landscape Information Series: U of MN. Be safe, G



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