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This summer I plan to start a small tree house for kids project on a old and big but living tree (Albizia julibrissin).
My first idea is to build a frame around branches without using screw in tree. The frame kind of capture branches.
Am I right to preserve the tree from being drilled for screw ?
Picture below shows principle for one branch but project will use as many as possible.
To illustrate @bowlturner's answer:
Your idea seems good at first, but I'm not sure it's the best idea long-term. For one, any movement caused by wind or by anyone moving around in the treehouse is going to cause the contact points from your brackets to rub against the bark. Over time, I could see this potentially damaging the tree more severely than bolts. Keep in mind that any part that's attached to the tree will also incidentally pull on parts of the tree that are attached to other parts of the treehouse. I would try to avoid attaching to any smaller limbs, and try to limit your attachment points to the trunk and perhaps a couple very large limbs that don't sway very much in the wind.
On the flipside, if your brackets don't damage the tree, they could restrict the tree's growth. If they don't damage the tree or restrict its growth, then as the limbs grow thicker in diameter they could move the treehouse's foundation and start to deform the treehouse, though this would take a very long time.
Family Handyman published a great article on building a treehouse, taking into account the tree's growth, using floating brackets, and many other practical considerations.
The design you are working on will work. Remember trees grow, no matter what.
Screws would work too. One thing I would point out the cross pieces you have connecting the two boards against the limb, probably shouldn't be wood. I would go with steel bolts. I would be afraid most wood would 'rot' or weaken relatively quickly against the bark, and it would have the bulk of the weight. On top of that the branch can 'easily' grow around a steel bolt, but the wood might be more likely to 'girdle' the branch.
The big thing your design has over nails or screws is that the branches can move without causing sheer forces against the nails or screws.
If you really don't want to screw into the tree. Maybe consider a post structure that is built around the tree branches. Then you would have the feel of it being in the tree but it would not be dependent on the tree.
