The Treehouse - Building the platform frame
With the supports in place, it's time to build the platform. The platform is built from two 12-foot 2 x 6 headers connected by nine 8 foot 2 x 6 joists. Joists should ideally be spaced 18 inches center to center. But the placement of the trees makes that impossible in some cases. So I tried to make the spacing less than that for those areas.
Because the main supports are so high (between 10 and 19 feet off the uneven ground), it's not possible to assemble the platform in the air. But since the trees will be rising between some of the joists, you can't fully assemble it on the ground either. I measured where the 4 joists between the 1 west and 2 east trees would be and attached them to the headers with 3.5-inch galvanized screws. Then I measured and attached joist hangers where the other joists would go. The center piece of 3/4-inch plywood was then attached to the headers and joists with many 2.5-inch galvanized screws to cover the center 4 feet of the 12 foot frame to stabilize it so it couldn't move laterally (as if it were a parallelogram) as it was being lifted.
Once that was done, I moved the platform so it was standing up on end, between the supporting beams (see the next picture).