I “Pinned” my Treehouse Beam. Now What?

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.

Options:
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.

4 Responses to “I “Pinned” my Treehouse Beam. Now What?”

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  1. Gary says:

    I too have pinned my treehouse, though I am in the early stages of building it (about half way through laying floor joist). I’ll try to describe what I’ve done. I DO have photos.

    Tree is oak and 3′ in diameter. I have two 4×4 posts positioned approx 10′ from tree which has beams attached to them (making a triangle between the posts and tree. I’m comsidering placing more posts if I go up with walls and a roof). My beams are doubled 2×6 with 3/4 ply sandwiched between (ply on its side offers more strength to the beam).

    Now the tree: I was originally going to run two 1/2 galvanized lag screws (somewhat staggered and not inline with each other) through each beam and into tree. Also, on the front of the tree (the side that would be inside of the triangle) I have a 2×10 lagged with two 5/8 screws sitting directly under the beams (almost cradeling) so as to help support the weight.

    All lag screws are at least 3 inches deap into the tree.

    I briefly considered using longer hardware on my all lag screws and leave an extra couple of inches of screw sticking out of the tree. This would allow both my beams and cradle room to migrate as the tree grew.

    I quickly decided against that.

    I am considering Granier fasteners, but would rather someone look at the photos I have first just to verify some things.

    If you get a chance to respond, thanks in advance.

    Gary

    • treetop says:

      Hello Gary,

      I think you are on the right track by considering garnier limbs for the tree. It’s the safe way to play it. With a 10x10x10x3 trapezoid, you’ll have about a 65 square foot platform. More than 50% will be held up by two posts because the platform is wider out there and can fit more people. So estimate the total dead weight of the structure, and then add somewhere between 30 and 100 pounds per square foot of potential live loading (depending on what building code you’re following) and then you’ll know how strong the fasteners need to be.

      For example, if you’re using 2000 lbs of materials (easy to do on a simple treehouse), and you have 65 square feet at 100 lbs per square foot, the you have 8500 lbs of total load. You’ll probably want the tree to support 3000-4000 lbs between the two attachment points. If Tree Top Builders was building this project for you, we would use a regular sized garnier limb into each side of the tree. In live oak trees in Oregon, some builders have estimated that a garnier limb will hold around 5000-8000 lbs when the load is placed 2″ out from the collar (and the garnier limb is installed properly). That is because oaks are much harder than average wood, so they hold more. The same garnier limb may only support 2000 in a pine or spruce. Furthermore, if the load is placed more than 2″ out, it will lose a lot of strength because of increased leverage. Be careful, and get an engineers or professional tree house builder’s opinion if you aren’t sure you know what you’re doing.

      Good luck and build safely…

  2. Tammy says:

    Help. I built a treehouse on broken main branches of a pine tree. The trunk of tree broke three large branches in a bad ice storm. So we u cut them flush horizontal and set the treehouse floor on top of them, built the rest from there. Five years later, fighting tree sap, we discovered that the tree is growing and pushing up on the floor. Posts are cemented at the base and nailed to the floor joists. We fear cutting them or the tree because of sap. Any suggestions?

    • thb98il1Tr3e says:

      Hello Tammy,

      It would help me to see a picture, but I would advise to not cut the tree when there is contact with the structure. Sap is the tree’s vitality, and sap will flow when a tree is cut. So, if your objective is to minimize sap, then it would be better to cut the structure away from the tree to allow space for growth and sealing (not healing). Eventually, the sap will reduce. However, some amount of sap in a white pine tree is normal. If that is what you are fighting, then you might need a roof.

      Good luck,
      -Dan

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