[jyl]

I do have a book, very useful. One thing I'm confused/uncertain about is anchoring into the trees.

I gather I should drill and screw a big (3/4" to 1" diam) lag bolt 6" to 8" into the tree, then secure the joist in a way that allows for trunk growth and tree movement, with the load perpendicular to the bolt shaft. I am also under the impression that you want as few holes in the tree as possible, my tentative design will use just one bolt per tree, using two trees about 8 feet apart. Is that all there is to it? Or is there some other trick/tip needed to avoid damage to the tree?

Will support one end of the platform with the trees, the other end w/ 4" x 4" posts set in concrete.

Hugh, what is the dimension of your joists? 2" x 6"? Adequate, or would you use 2" x 8"?

I think I need to overbuild this so that if I do attract the attention of the authorities, at least they won't be able to call the structure unsound.

Guess I need to look at some spanning tables.