Question from Randy, Milford, DE:
"I just “finished” a treehouse for my kids and while looking around on the net, came across your site. After reading over it, I realized that I made a cardinal error and “pinned” one of the support beams to the tree. It is a large Oak and I have a 2 x 12 lag bolted to it with about three 6.5” x ½”. The front half of the treehouse platform is supported by two 2 x 12 beams bolted to two 4 x 6 posts. Obviously, the beam that is pinned to the tree will create problems in the future. Is there a “simple” solution that I could implement to save the tree from trauma and the house from falling down in the future? I can send photos if you would like. Where are you located?"
First of all Randy, you are not alone. We regularly hear from people just like you who want to support their treehouse in a better way. There are multiple issues here that may be at play. It would help to see a close up photo or two of the area where the treehouse beam and tree connect, and it would help even more if you hire us or a local arborist to inspect it. Sometimes, we see things in person that are not noticed or describes over email/photos.
1) You can leave it alone and keep an eye on it. It might be okay for a while, and if the tree is growing around the beam, and doesn't appear to be suffering too much, you may decide to let the tree deal with it. How valuable is your tree? $1000? $25,000? How much did your treehouse cost you to build?
2) You can hoist or jack the treehouse up, detach the beam from the lag bolts, and install a larger fastener such as a garnier limb underneath the beam, and then set the house back down on the larger fastener. This runs a risk, because you already made 3 holes close together, and now you're adding another one only a few inches below. This is a good move if the wounds in the tree do not coalesce. You could also choose to raise or lower the whole treehouse to prevent the wounds from being so close together.
3) You could permanently suspend each side of the treehouse beam to points higher in the tree. Make sure you are comfortable with cabling and working at that height, and use cable that is rated for at least double the total dead and live load that will be on it. The advantage is that the new wounds will be far from the other ones. But it does mean working higher in the tree, and attaching loads higher in trees means more sway and possibly greater chances of storm damage depending on how high you go up.
4) Your backup plan, if the tree is suffering and #2 or #3 won't work or the risks aren't acceptable, is to add two more posts near the tree and a new beam. When you remove the old beam, if possible, don't remove the lags that go into the tree unless they are loose in their holes. You may cut them flush to the outer bark if desired. There may be other options or considerations that will come to mind if we can see the tree and treehouse, but we're likely to choose one of the above.