One Tree, Two Posts Treehouse Plan

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Personalize your treehouse by adding on accessories such as swings, rope ladders, or zip lines.
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Enhance your backyard space by building your own treehouse with these easy to follow instructions for a one tree, two posts plan.
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Enhance your backyard space by building your own treehouse with these easy to follow instructions for a one tree, two posts plan.

InBackyard Treehouses: Building Plans, Tips, and Advice, Dan Wright offers readers expert advice to readers wanting to build a treehouse in their backyard with limited time and money. The book offers a variety of plans from simple to complex, as well as step-by-step photos, building plans, and helpful tips. The book is perfect for readers who want to build a safe backyard treehouse for their families, while minimizing the impact on their trees. The following excerpt is from Chapter 5, “Common Treehouse Plans.”

Stage 1:

  • Install one TAB 3 x 9 bolt and pipe bracket at desired height in the tree for the top of the tribeam.
  • Be sure to have your pipe bracket on the TAB before you turn it into the tree.

Stage 2:

  • Build the tribeam on the ground and then, with help, lift and attach it to the pipe bracket located on the top TAB bolt. A rope and pulley system makes this easier to lift, especially when building out of easy reach.
  • Once it is in place, hold the top part of the tribeam level, and then mark the location for the bottom TAB through the hole in the bracket at the bottom of the tribeam.
  • Drill for the bottom TAB, but we suggest tilting the tribeam and inserting the bottom TAB into the bracket before turning the TAB into the tree. We can usually put this TAB in the tree without disconnecting the Tribeam from the upper TAB and bracket.

Stage 3:

  • Lay out and build your concrete footings to support the 6 x 6 posts and beam.
  • Carefully use a laser, water level, or regular spirit level to notch the posts for the beam to ensure that the top of the tribeam is level with the top of the beam on the two posts.
  • For a 10 x 10 single-story treehouse, a double 2 x 12 beam should be sufficient, or a double 2 x 8 beam with properly connected angle braces to shorten the span.

Important: Check your local codes to determine footing size/depth.

Stage 4:

  • Next, cut all joists on ground and attach them to your beam and tribeam. We suggest screwing the joists in place instead of nailing so that if they need to be shifted, they will be easier to modify. I advise leaving 3 to 6 inches of space between joists and the tree to minimize future maintenance as the tree grows.
  • If needed, use temporary bracing on the porch to hold the platform level while working. You do not have to angle the porch joists as shown; we normally do for aesthetic reasons, but you may leave them square if desired, which is actually a little bit easier to build.
  • If you choose to install a trapdoor, the easiest location is in line with the tree trunk, either on the porch or inside the house. Framing it in line with the tree will minimize the disruption of full-length floor joists.

Stage 5:

  • After all joists are installed, add knee braces, one at a time.
  • First, check that your temporary bracing is holding the floor joists level. Then we suggest cutting a notch into the top of the knee brace to fit the platform frame.
  • Next hold the knee brace up in place to mark the length of the bottom. Then bring the knee brace down to a work table, cut the length, and install the knee brace bracket into the wood.
  • Last, hold the finished knee brace up in place, screw the top notch into the rim joists, mark the center of the hole on the tree through the bracket, predrill the hole, and turn the bolt into the tree right through the bracket. Repeat on the other knee brace.
  • Depending on the length of the cantilever and width of the deck, you may need two or three knee braces. Two are shown, but if adding a third, it should go right in the center in line with the tree trunk.

Stage 6:

  • Install 5/4 x 6 pressure-treated decking or another exterior decking material of your choice. If desired, you may put a plywood subfloor down for the portion of the deck that will be enclosed instead of the deck boards.
  • We recommend using 2-1/2-inch decking screws with a torx head, such as the GRK R4 screws. Screws are a far better choice than nails for flooring.
  • Be sure to leave a 1- to 3-inch gap around the tree for growth expansion. If you chose to install a trapdoor, cut out the flooring in that area.

Stage 7:

  • We suggest framing all the walls on the ground and lifting them into position with the help of a friend or hoist system. However, if you don’t have a flat spot on the ground, and the platform is large enough, then it may prove easier to frame the wall lying flat up on your completed platform.
  • Frame the window and door rough openings per the manufacturers’ recommendations.
  • Next, determine the pitch of the roof and the amount of overhang you want. Build your ridge and install it in place with temporary supports. Install the roof rafters.

Stage 8:

  • Install the wall and roof sheathing, as well as your roof felt. If your treehouse will not get a finished interior, then consider using two layers of roof sheathing so nails don’t stick down and show from the underside.
  • If the roof is high out of reach, then this may not matter to you.

Pro Tip: Where possible, let your wall sheathing extend down past your wall’s bottom plate, and attach it to the side of your floor joists as shown. It will lock the treehouse to your platform, which will make it very rigid and prevent flexing or sagging in your floor joists.

Stage 9:

  • Install your windows, doors, choice of siding, roofing, trim, and railings.

Stage 10:

  • Install accessories such as swings, rope ladders, cargo climb nets, fireman’s poles, zip lines, and anything else you have your heart set on.

Excerpted with permission fromBackyard Treehouses, by Dan Wright. Published by Lyons Press, © 2018.