Build your supports
No matter what kind of tree you’re building out of, you will need supports to hold up the house. At the risk of oversimplifying, we’ll narrow the types of supports down to two types—ground-based and tree-based. With tree-based supports, you’ll need to have two-by-four beams at each corner and on each side of the base. The beams will extend downward from the base at a 45-degree angle until lodged against a common fixture, which will be fastened against the tree. With ground-based supports, two four-by-four posts will be inserted into the ground with concrete and extend up into the corners of the house, which will extend outward from the tree.
The floor and supports will be built simultaneously, and like the supports, the floor will need something to stand against. At least one side of the base will need to touch the tree, which will be bolted in with lag screws and have additional diagonal bracing for extra strength. The floor should be a frame of beams in the shape of a rectangle. Plywood will then be placed upon the top side of the frame and will be nailed in over each beam it crosses. For this part of the project, you’ll need two-by-fours, plywood, adhesive, and screws for the floors.
Depending on what kind of treehouse you’d like, the sides of the platform will vary. Some treehouses will have sides that extend upward to a roof; others will simply have railing. For railing, bolt four-by-four posts into the corners and sides of the floor that extend upward. From there, take strips of decking that extend the length of the floor and run them horizontally along the inside of the beams. For walls, make a frame similar to that which was made for the floor (except not as heavy of wood) with one having a door-sized gap for an entryway and spaces for inserting Plexiglas® windows. Bolt the frame to the edges of the floor while fastening each at the corner. Once the frames are up, nail slabs of wood siding to the outside of the frame.
You’ll need a ladder to get into your treehouse, and fortunately, building one isn’t difficult at all. Measure the distance from the ground up to your treehouse and bring as many two-by-fours as needed to reach the floor of the house (if needed, nail 2-foot segments of two-by-four on the outside of the connecting points of the ladder rails to fasten them together). Make as many 2-foot segments of two-by-four as you need to place every 1 1/2 feet going up the ladder. Drill diagonally into the steps to fasten the steps into the rails. Finish by drilling the top of the ladder into the side of the treehouse beneath the entryway.
Not every treehouse has a roof, but we decided to include a section if you decide to go that direction. There are several ways to build a roof, but we decided to go with a simple way for your own convenience. Begin by cutting a piece of corrugated plastic to the dimensions of your treehouse floor with about 1-2 additional inches on each side. If the tree emerges through the house, do the same with two overlapping pieces of plastic that account for the tree’s circumference. Once the plastic is sitting on top of the walls, fasten it with wood screws along the top of each wall.
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