Matt's suggestion of steel bracing has the wheels turning. I've changed my mind on the dock design though and have 5 extra 12' 2x6s ... seems like those would work well for X braces on each side of the treehouse, and one diagonal brace under the joists. I also have a few unused 8' treated 4x4s in the barn that could be cut up for Y braces so that will be tempting. I've read that 2x4 bracing should not span more than 6' and these diagonal braces will need to be around 11' long, hence the idea for using 2x6's. The deck platform itself is 8x8 and everything with any load on it is tied together with 3.5" x 3/8" galvanized lag screws. The balusters are put up with the 3.5" gray outdoor treated deck screws.
Brettski, I vist your dock building thread so often the URL is practically committed to memory
Hope you don't mind me pilfering a few ideas here and there.
Eric
