# sub a 6x6 for an 8x8? treeless tree house

Discussion in 'General Home Improvement Discussion' started by Philphine, Apr 4, 2009.

1. Apr 4, 2009

### Philphine

#### don't give him tools!!!

Joined:
Feb 28, 2007
Messages:
128
2
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.

2. Apr 4, 2009

### Nestor_Kelebay

#### Emperor Penguin

Joined:
Mar 29, 2009
Messages:
1,844
2
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/~jbut030/Courses/CIVIL211/Column_Buckling_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.

Last edited: Apr 4, 2009
3. Apr 4, 2009

### inspectorD

Joined:
Dec 17, 2005
Messages:
4,502
267
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.

4. Apr 4, 2009

### jdougn

#### Well-Known Member

Joined:
Aug 7, 2006
Messages:
132
1
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

5. Apr 4, 2009

### Philphine

#### don't give him tools!!!

Joined:
Feb 28, 2007
Messages:
128
2
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.

6. May 28, 2009

### rvblevins

#### New Member

Joined:
May 28, 2009
Messages:
1
0
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

7. May 30, 2009

### Philphine

#### don't give him tools!!!

Joined:
Feb 28, 2007
Messages:
128
2
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

Last edited: May 31, 2009
8. May 31, 2009

### DaveyDIY

#### Extreme DIY Homeowner

Joined:
Apr 14, 2009
Messages:
82
2
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

9. Jun 8, 2009

### kmwisinski

#### New Member

Joined:
Jun 8, 2009
Messages:
1
0
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?

10. Jun 8, 2009

### GBR

#### Well-Known Member

Joined:
Mar 18, 2009
Messages:
402
38
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

11. Dec 22, 2009

### Bozeman

#### New Member

Joined:
Dec 22, 2009
Messages:
2
0
Any updates? We're digging the hole today and the pole gets delivered tomorrow morning. I think we have a pretty good handle on the platform but, as mentioned above, the lack of detail on the upper structure has me scratching my head a bit. A couple of basic questions:

1. How does the 2x6 top rail fit with the 2x8 vertical corner boards? 45 degree mitres and then notched out to fit flush with the corner pieces?
2. How are the 2x4 diagonal braces ("C") configured? It seems the sketchy plans have not accounted for the offset between the corner boards and the headers.

Haven't even started figuring out the roof yet. It would be great to hear from those that have been through this already.

Thanks

12. Dec 25, 2009

### Philphine

#### don't give him tools!!!

Joined:
Feb 28, 2007
Messages:
128
2
none from me. i still intend to build them but have gone on to other projects 'til i figure out what to do about the posts i need.

13. Dec 25, 2009

### Bozeman

#### New Member

Joined:
Dec 22, 2009
Messages:
2
0
The more I thought about the eight lag bolts in the same plane and the heavy norwesters (can hit 100 mph) we get here, the more I didn't like the design. The guys at the local building supply store agreed and we have cancelled the project. We may simply change this to four smaller posts rather than the one big one. Should not only be stronger but more stable and easier to build.

14. Dec 29, 2009

### Philphine

#### don't give him tools!!!

Joined:
Feb 28, 2007
Messages:
128
2
i think i might have a line on an 8x8 from a local mill. haven't got all the details yet but the main thing that concerns me is it won't be treated.

if i went with it, is there anything i can do myself to make up for it being untreated, or maybe i should pass on it?

15. Dec 30, 2009

### Philphine

#### don't give him tools!!!

Joined:
Feb 28, 2007
Messages:
128
2
heard back from the mill and they say they can't recommend untreated pine for what i want either, but they do think black locust they have will work fine.

about to do a little googling to read up on it. the price seems pretty good. anyone know much about wood types?

16. Feb 17, 2010

### Philphine

#### don't give him tools!!!

Joined:
Feb 28, 2007
Messages:
128
2
my 8x8's were delivered today. can't do anything with them now, with the season and weather, but i think they're going to work for me. they're huge, and true 8x8's, actually about 8 1/8".

i went with the untreated black locust from the local mill. i read as much as i could find on it and i think i won't end up regreting going with it, but i'm going to keep reading since i have a while before i actually plant them to see what i might be able to do to them myself. like a paint on treatment, method of planting or something, for the best results as far as making sure they last.

so hopefully come spring i can start working at it again.

17. Feb 17, 2010

### Wuzzat?

Joined:
Jan 20, 2010
Messages:
2,471
175
There'll be a torque on the upright when the wind blows due to the house acting like a sail.

I'd find this 99th percentile wind value for your area and check if the upright and the footing for it can withstand this torque.
For the upright it's a bending force; for the soil it's probably a shearing force and/or compressive force.

You might consider guy wires.

This project has high potential for a Darwin Award.

18. Feb 17, 2010

### Philphine

#### don't give him tools!!!

Joined:
Feb 28, 2007
Messages:
128
2
actually the thing i'll be wringing my hands over is lining up the two structures.

19. Mar 14, 2010

### Philphine

#### don't give him tools!!!

Joined:
Feb 28, 2007
Messages:
128
2
8x8's planted. one last weekend and one today

i read all i could on the 'net and the suggestions here, mostly 'cause i'm still a little apprehensive about untreated wood. from what i can find people seem pretty confident about this type of wood if you find a good piece. i still tried the putting gravel in the bottom of the hole and set a concrete paver on the gravel. i didn't do the wrap in plastic though. i kept thinking i'd tear the bottom of whatever plastic i tried and then it would just work to keep water around it instead. i did try painting the bottom of the poles with used motor oil, i saw that on one of the black locust sites and it seemed like a good idea.

so far so good. i think i lined them up pretty well. threw levels at it every way i could think of and still kept checking the first one all this last week. the one thing i still need to do is match the heights. i figured that's the one variable i can still correct after they're planted so i sacrificed that to make sure the other things. i used a line level preliminarily and one is about 1 1/2" taller. i'll give it some time to make sure the concrete sets and even them up.

so i'm finaly started. i have a million scatterbrained projects going though so who know when i'll get it done.

20. Mar 25, 2010

### Philphine

#### don't give him tools!!!

Joined:
Feb 28, 2007
Messages:
128
2
my slow progress

the two middle joist. they're sitting on notches in the posts and being held by 4-3 1/2" screws (pretty much to line things up and keep them in place) and two 1/2" bolts.

so far so good. there are a couple more joist sections i need to line up just so (that deal with the two structures being linked), but so far as i line up strings and levels it seems like they'll match up ok. one mistake was when i dug the holes i somehow must have not centered them well enough distance wise. they're about 7" closer together than i want (about 19'5"). not a big deal for the structure it's self, but since it's dual purpose to hold a theater screen i wanted to be 20' wide, i'll need to tweek the screen build when i get to it. shouldn't be too big a problem.

this is more a pic for me. as stated, i want to be able to use the playset to brace a theater screen, so i set a couple of 6' 2x4's on the joist to kind of eyeball the overall width, and sit around the area and get a feel for viewing the planned screen.

bettween weather and cash i'm on hold for a bit. hopefully i'll get a little more done this weekend.

Title
Replies Views
Last Message

Replies:
1,736
Views:
391,827

Replies:
58
Views:
901

Replies:
3
Views:
36

Replies:
1
Views:
161

Replies:
9
Views:
172