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Before you begin your framing, refer back to your plans. There are basically 2 different ways to support and frame a treehouse. One is to have the weight of the treehouse supported by just the tree. This is ideal for higher treehouses that cannot reach the ground.
The other option is to have posts going from the treehouse to the ground. With this option, parts of the treehouse are often supported by the tree and also the supports. This is the easier option (since you don’t have to worry about angled cuts as much) and is ideal for treehouses that are closer to the ground.
For our treehouse, we used a combination of the two, with most of our support coming from posts down to the ground (note: the highest part of our treehouse is about 7 ft off the ground). To keep it simple, we’ll be focusing on that method here.
1. Set your support posts.
Since these posts will be supporting the bulk of your treehouse, it is important that they are solidly set in place. You can either do this by digging a hole and cementing it in or using pre-fabricated concrete post blocks. Our initial plan was to cement the posts into holes, but digging out a big hole this close to the tree roots turned out to be a nightmare. Honestly, the post-blocks were a piece of cake and I’m so glad we went with those. Not only are they simple, but since the posts are not cemented down, it allows the treehouse more flexibility (during wind storms or when the tree grows). Whichever way you choose to set your posts, make sure that they are squared to where the rest of the framing will be going, and that they are level.
2. Install cross-beams and connect to the tree.
Once your support beams are in place, the next step is to tie those into the tree with cross beams. Although it can be tedious, take your time on this part. If you are sloppy here, the rest of your treehouse will show it. Essentially your goal is to make the outer frame that all of your planking will rest on. To do this well, you need to factor in two things: Level boards, and good contact with the tree. To get good contact with the tree, it is often necessary to cut out/smooth small sections of bark out. By doing this, you can ensure that your boards have more points of contact with the tree (um sorry no picture of that). To connect the cross beams to both the tree and the support posts, we used lag bolts. These things are tough (and tough to install). Unlike simply using screws, lag bolts are LONG and THICK providing a good anchor point. We used a combination of 6″ and 8″ bolts depending on how many pieces of wood we were screwing into. If you’re lucky, you have an impact wrench (or can borrow one) which will make this much easier. If not, you can do what we did and use a combination of drilled pilot holes, sockets on the end of the drill, and a socket wrench to finish it off.
3. Install corner braces.
We completely underestimated how important these were going to be. These braces (which we installed 2 of at each corner) took the frame from being wobbly to solid as a rock. Simply angle a 2×4 on each end and screw it in place (note: since we chose to put these on each corner, we had to insert an extra block of wood behind each corner cross beam from step 2 to make sure that they fit correctly).
4. Insert middle beams.
Unless your treehouse is really small, you will need to have some center supports on your decking area. Don’t skip this step, because it’s really one of the easiest. Cut your beams the length of the inside of the frame. To secure them, go to the hardware store and get some deck braces. All you need to do is to screw them in, slide the beam in and insert another screw to hold it in place – easy!
Now get excited, you’re almost done! Check back soon for our final treehouse installment – decking, railing, and finishing touches.