Roberto pokachinni wrote:From the pics, I would try to figure out a few things first, but paramount is: Is the structure, as is, worth keeping? I'm not saying it's not, but it's small enough that renovating might be more of a hassle than removing the existing structure and building exactly what you want. If you have the materials to build a structure, then it might be better to start from scratch.
The reason I would consider scrapping it is because there is visible deterioration all over it, including splits and cracks where it was screwed or nailed, and green growth on it, and other features in looking at the photo's that seem to indicate to me that the wood is not in the best shape. I bet it is really heavy after a rain at this point, due to all of the fungi, algae, mosses, and whatnot sucking moisture into the wood and holding it there.
So, other things to consider, if you are planning to add to the structure after assessing if it's worth it, are the size of hardware that are fastening the various parts to the tree. Are they going to be able to handle more mass? If not, can they be replaced by beefier items?
What kind of wood is the supporting structure and platform made of? Some woods are considerably better at supporting weight in a horizontal position than others. It may be holding up just fine now, but might not with the addition of walls, roof, windows, door, etc.
Is there a possibility of bracing the structure with heavier beams and hardware from below?
Lagging your supporting beams with heavy hardware is the best way to attach to a tree. The tree will suffer briefly, but will sap out and heal the wound where the lag screws in.
Pre-drilling your boards will help the boards not to split.
I will not be replacing the existing supporting beams as those didn't take much beating from being under and they're already attached pretty welll.
With the 2x6 support beams mostly angled or bolted to the bottoms of trunks, I would be reluctant to add to the load (square footage) without also adding more support.