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Discussion Starter · #1 ·
Hi all,
I have been looking around the internet for a couple of months, and I ended up with the following layout for a treehouse platform. I have some experiance in light DIY projects but it will be my first time for something that big and complex. So any advice on anything looking wrong would be great. It is based on what other people around the web have used for similar size treehouses - other than using steel string instead of knee/diagonal braces(there will be 4 strings - picture shows only 1 of them).

Platform surface is roughly 6.5' x 6.5' (2.2m x 2.2m) plus a small deck
Parts (from bottom to top):
- 4 x lag screws 3/4"x12" (20x300mm)
- 2" x 10" main beams, 10.5ft long (3.5m)
- 3" x 6" parallel beams (with the eyebolts)
- 2" x 6" vertical beams (no eyebolts)
- joist hangers and rafter ties to join all the beams
- 1" x 5" planks for the floor (I already have them in stock)

I have not decided yet on the size of steel string, eybolts and turn-buckles. A rough calculation of empty (without people) weight is 1000 lb, so I guess buying components so that each can bear 1000 lb will be ok (there are 4 of them so all combined will be able to hold up to 4000 lb i.e the empty house, people on it plus a big safety margin).

Pic1: Platform layout. 4 strings (picture shows only one of them)
Pic2: Bottom of platform, under the small deck
Pic3: The real trees with a test plank (for measurements)
 

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How high up are you going ?
At reasonable heights, I would seriously consider building on posts. You have known strengths of the materials vs the unknown strength of the trees.

I don't think the kids would really care. The elevated playhouse is cool too, and it doesn't pose risks to the trees.
 

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I did a similar one a few years ago. It looks like you are allowing for the movement of the trees. I fixed it to one trunk and allowed it to slide over supports on the second trunk. One thing I did was make a trap door to with a ladder midway to a platform at a midway point and then steps down from that. I was afraid of someone falling through the trap door. At least now there's a platform halfway down to catch them. I did a gambrel roof and doghouse windows too.
 

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Discussion Starter · #5 ·
Ayuh,.... What's the detail of how yer attachin' to the trees,..??
Ya know there'll be movement,..??
Also gotta be careful not to damage the bark, 'n girdle 'em,.....
The picture below shows the details.
The tree is 20" (50cm) thick, but it has a thick 2" bark that is brittle. The plan is to use a hole saw all through the bark and then put in the hole some spacers. I will also use a short length of pipe for the part of the lag screw that will hang out (and support the beam). So, out of the total length or the lag screw (12") the first 7" will be inside the core of the tree, the next 2" will be inside the spacers to account for the bark and the last 3" will hang out and support the beam.

These trees can handle more abuse than this. I also asked the local agriculturist just to be sure.

How high up are you going ?
At reasonable heights, I would seriously consider building on posts.
The floor will be 7 to 8 ft high (the ground is tilted). I really want a free space under the platform, no posts and no knee braces. If I fail in this, I will abort the project and build a playhouse on the ground.

I was afraid of someone falling through the trap door...
That's something I have been thinking how to deal with...
I don't know if the midway platform solves the issue - when one foot will be on the treehouse and the other over the open trapdoor, you will loose balance and hit a head on the walls.
I was thinking of a light counterweight that will keep the door closed (unless force is applied) plus a bar which will sadly limit the space in the house plus a strict procedure for how the kids climb on and off the house. But that's for later.
Do you have any pictures or any building thread with your treehouse?

 

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I tried to arrange the platform diagonal to the trees. This puts the trunks in the corners and leaves more room for activities. I also thought it would be more stable with the braces at the opposite corners. The floor joist are 2X4 and I think the beams are 2x6 maybe 2x8. They are short spans. I used osb for the floor and the walls are also osb t1-11. I used short 3/4 inch roofing nails so they wouldn't penetrate through to the other side. You can see the platform I mentioned
 

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That is a layout to fail. There is a reason that those companies that professionally build tree houses, have special hangers and understand that the tree is a living object.

No city is going to let a treehouse held up by wires and turnbuckles to pass, since they have started to be more alert on these items, then how it was in the 70's and before.
 

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I didn't know about these sites 10 years ago when I built mine. I used long lag bolts. I figured they are good enough for attaching a deck ledger to a house. Had I known about the specialized hardware I would have opted for that-much safer, and easier. Only half the weight of my house is borne by the lags though, the other half by the diagonal posts. After 10 years, the tree has begun to grow around the beams, even if the lags failed it can't go anywhere it's part of the tree. As far as code goes, I doubt any tree house, regardless of how well it's built, is legal in my town. You should look into that or be ready to take it down. Mine has survived two hurricanes and 3 boys.
 

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If you're a fan of This Old House, they just built a fancy tree house on an episode I saw a few weeks ago. You can probably find info on the construction specs at the This Old House website.
 

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They just started making the hardware about five years ago. Before that, they were retrofitting existing hardware.

Tree house building is no longer about kids. There are people who have them built to live in or even have as a weekend getaway.
 

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Discussion Starter · #14 ·
@TimSBLI:
nice treehouse you got there. Well done.

@gregzoll:
I appreciate your comments. What do you think would be the most likely to fail part?

As far as I have understood (and my knowledge on construction is next to nothing) wires and turnbuckles, depending on thickness and specs, are used for heavy weights. In my case they will be used only to replace the knee braces - the main support will be the 3/4" lag screws.

I have been referenced to the treehousesupplies site again, but I think that their hardware is for bigger projects. The same holds for TV shows on the subject. They show crazy projects, more like ordinary houses on a tree than a small playhouse for kids.

PS: I forgot to mention that I live in a place where rarely snows and no hurricanes.
 

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I do not like the lag bolt attachment in the photo in post #5. Lag bolts are designed to be pulled up tight. They are rated for tension and shear. I have never seen a rating for a lag screw bending with x inches of projection.

The other thing is that strap underneath. What is the straps resistance to bending and what are the screw attachment pull ot ratings on it ?

It looks like a "close enough for government work" type installation rather than proper design.

If you get a lifting moment on that platform either by wind loading or failure of another point of support, will it really hold the platform in place, or does it fail allowing the platform to tip further ?

I think I would toss that design and reinitiate my search for a better design. Or go to your backup plan and build the playhouse on the ground.
 

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Did you watch that TOH episode? I assure you that Tommy Silva knows what he is doing and they built a great little treehouse that will last 50 years.
I have not watched that show for almost 10 years, because of the change of format and it was becoming too comical with some of the stuff thatthey do.

I will stick with shows that actually talk about what they are supposed to. At least Treehouse Masters stay on format.
 

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dj31 it has nothing to do with weather and where you live. It is about safety and keeping a person from losing everything if aomeone's kid or an adult gets hurt when that design fails.

The reason for the special brackets and properly designing the structure, is because it is less to have a point of failure.

Those cables and turnbuckles would not last long, once some kid starts jumping up and down, along with those lag bolts will end up working their way out.
 

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Discussion Starter · #20 ·
The other thing is that strap underneath. What is the straps resistance to bending and what are the screw attachment pull ot ratings on it ?
.
Thanks for pointing this out. I had in mind something like a 1/8" thick strap attached with 1/4" lag screws as this part won't bare any load.
But if the platform lifted there would be a serious problem...

Lag bolts are designed to be pulled up tight. They are rated for tension and shear. I have never seen a rating for a lag screw bending with x inches of projection.
Just for the record...If the lag screw is pulled up tight against the tube & spacers as in the diagram below,assuming a tight fit in the tube and all threaded length of the screw is in the tree, is it still considered as projecting?

@gragzol and all the others:
I won't build anything as long as I m not 100% convinced that it is reasonably safe. I don't want to risk anyone's life. So far my design has a status:"red and about to be discarded".

 
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