I set out to build a treehouse today. I have this great tree that has a notch where two limbs branch in a "V". The notch is about 8 feet off the ground and the tree is in the corner of my yard. Because of the height, I constrained my design to a double decker treehouse and really liked this site:
http://www.diynetwork.com/how-to/how-to-build-a-double-decker-playhouse/index.html
This post has good info on digging postholes:http://www.familyhandyman.com/garden-structures/fences/how-to-dig-a-hole-pro-tips/view-all
In addition to the lumber and bolts, all I really needed was the digging bar (borrowed), clamshell digger ($40 at HD), and I got a short $10 utility shovel really for the kids but it turned out to be really handy to dig out some rocks and the like.
I got one of the 4x4s set in a posthole I dug - it wasn't too much work at all. With the recommended 36" postholes, it looks like I will need a bag of rapidset cement per post. This first post is inline with the tree notch, so the next step is to set the crossbeam joist from the tree notch, level it and attach it to the 4x4 post. Then I will add the other 2 posts and put a deck on this platform. I'm going to start there and add on modularly to spread out the work, and let the kids weigh in on what they want to go into the design.
The one open question is if I should just rest the crossbeam in the tree notch or tie it with rope by lacing around a figure eight around the beam and tree branches. I've read some that rope can strangle a growing tree. These sites seems to indicate resting in the tree crotch is fine:
http://www.ronhazelton.com/projects/how_to_build_a_tree_house_or_tree_fort
http://www.johnderbyshire.com/Treehouse/Phase_1/page.html
This site recommends adding some rope but I think that may be relevant if no ground posts are used:
http://warnell.forestry.uga.edu/service/library/index.php3?docID=133&docHistory%5B%5D=2
For finishing touches, this site seemed thorough:
http://www.dorothyainsworth.com/tree/house.shtml
Do you know of any other good information sources for treehouses?
