Will this have a roof?

No roof planned, just deck & railing. Snow loads calculated based on a worst case (flat, exposed roof) scenario. A sloped roof would perhaps double dead load (to 20 lb/sq. ft), but it might significantly lower the snow load, for no net change (but would need to check, if it ever comes to that). By the way, the snow load is almost half of my total calculated load.

Decking + tension cable sounds like a good plan (even though the wood won't last 500 years!). I don't want this to fall down.

Gave some thought today on how to assemble this thing...a bit tricky. I think two temporary guy ropes/wires from ~3 feet out on each beam back to the tree, ~3' above the planned attachment point and off to either side, will let the beam dangle in place, allowing "easy" adjustment of horizontal (level) and lateral (perpendicular to tree) positioning. I can then mark, drill, and bolt in the beam support block, fit the strut, mark/drill/bolt it's block, etc. Also plan to tack on a temporary 2x4 between the beams to give lateral stability, prior to proper decking installation.

Fun project, but it is taking some serious time & work! Thanks for all the great ideas and suggestions.

I was thinking of a different direction for the frame system.
One that wraps around the tree and gives some space for the tree to grow in diameter.

Just a thought.

Rooster

Hi Rooster, I considered that but I couldn't think of how to do it.

The tree is pretty large already (weeping willow, ~3' diameter, topped off by a storm at ~25' and now putting on a new "head of hair"), so I'm hoping my radial beam arrangement will work for a decade or two. As the tree grows I think I may need to trim the innermost decking, so that it doesn't strangle the tree. I plan on leaving a ~3" gap between the deck and the tree to delay this eventuality.

At some point, I might need to loosen the lag bolts a bit, to relieve compression on the support blocks as the cambium grows outward. I might even need to replace all the decking/rails eventually, lest they get slowly driven into higher and higher tension.

On the other hand, I have read on several tree house sites that trees often grow around support structures, especially if they don't make a band around the tree [which is considered bad form], just slowing enveloping the supports in cambium/bark. That's why I went with radial support beams (even though they're really a pain to attach to the tree!)

I'm too far into at this point to do a major redesign, but I would be interested to learn how what you suggest might be accomplished!

David

photobucket not working nicely for me, but I managed to grab one of your images, the one with the iris-like, pseudo-tangential supports. Picture re-posted here in case others are having trouble accessing it also: Rooster's Design

Don't you think this design would strangle the tree as it grew? The timbers can't open like an iris unless there were no decking, though I suppose you could have floating deck plates that could move past one another...

Well, for starters, it isn't timber-framed. The joists are 3x8 and timber-screwed together...creating an inner circumference that is larger than the widest part of the tree trunk. The joists could be pre-assembled flat on the ground in 4 seperate sections... with a 2x4 temperarily securing the tops of the joists, in each section, in the precise orientation. Each section could be lifted into position, secured to the trunk with timber-screws and using a spacer block, and supported by using a couple of 2x4 as legs under the ends of the joists. Each section can be secured to each adjacent section around the trunk. Truts can then be installed to transfer the load...and the "legs" can be removed....or something like that. haha

Good luck,
Rooster

The inner diameter is set large enough to allow the tree to grow during the lifetime of the deck...25 years? Removeable blocks can be changed out as the tree grows.

Interesting idea. Strut support blocks would be removable/replacable? Also, would the structs act not only to support the load but also to prevent any sway (as the round "hole" in the middle would not actually touch the tree)? Seems really tricky...

P.S. - your pictures I couldn't see: IE vs. Firefox; the TFG forum seems to play a bit better w/ IE.